Summary

The stomach is an organ of the digestive tract that is located between the esophagus and the small intestine. The stomach is lined by columnar epithelial cells and glands that secrete a thick layer of mucus. Beneath this surface layer (called the gastric mucosa) is a thin layer of smooth muscle cells (muscularis mucosae) on top of loose connective tissue (submucosa).

Stomach cancer (also known as gastric cancer) has few early symptoms, is usually diagnosed at late stages, and has a high mortality rate. It is the third leading cause of cancer-related deaths worldwide after lung cancer and colorectal cancer (1). Lifestyle factors, in particular dietary habits, along with bacterial infection and family history, have been identified as important determinants of the risk of developing stomach cancer.

DEFINITIONS
Gastric mucus - a glycoprotein layer that protects the lining epithelium of the stomach cavity and lubricates food masses in order to facilitate movement within the stomach
Glycoproteins - proteins with short chains of sugars (oligosaccharides) attached to amino acid side chains

Disease Overview

Incidence

In 2018, 1 million people worldwide received a diagnosis of stomach cancer (1).

  • The disease affects more men than women: 15.7 new cases per 100,000 among men versus 7 new cases per 100,000 among women (1).
  • The highest incidence is observed among populations living in Eastern Asia, where the incidence rate is 32.1 per 100,000 among men and 13.2 among women (1).
  • There are great variations in incidence across ethnic groups. In the US, there are two new cases of stomach cancer among Blacks for each new case among Whites.


Over the last five decades, the incidence of stomach cancer has been declining. This decreasing trend is attributed to several factors (2, 3):

  • Improvements of living conditions, specifically with better food preservation and refrigeration;
  • Decrease in salt consumption;
  • Greater inclusion of fresh fruit and vegetables in diets;
  • Decrease in the use of tobacco;
  • Decrease in exposure to Helicobacter pylori.
DEFINITIONS
Helicobacter pylori - a bacterium described as a group 1 cancer-causing agent by the International Agency for Research on Cancer since 1994
Incidence - proportion of new cases of a disease in a given population at risk over a specific period of time

Classifications

More than 90% of cases of stomach tumors are adenocarcinomas.

Stomach cancers can be identified according to their histological features (4):

  • The intestinal type refers to well-differentiated tumors, which are usually more prevalent and often have a good prognosis.
  • The diffuse type refers to poorly differentiated tumors, which are more prevalent among younger adults and women and are often associated with a poorer prognosis.

Stomach cancers can be classified according to the anatomic location of the cancer:

  • Cancers of the gastric cardia arise in the region close to the esophageal-gastric junction. They are often associated with gastroesophageal reflux disease and resemble esophageal adenocarcinomas.
  • Non-cardia cancers arise from other parts of the stomach. This subtype is primarily related to Helicobacter pylori-induced atrophic gastritis.
DEFINITIONS
Atrophic gastritis - a chronic inflammation of the lining of the stomach, which ultimately results in the loss of glands in the stomach (atrophy) and decreased stomach acid production
(Gastric) adenocarcinoma - type of tumor arising from glandular cells of the gastric mucosa
Gastric cardia - upper part of the stomach adjacent to the section where the esophagus opens into the stomach
Gastroesophageal reflux disease - a condition in which the stomach contents, including acid, back up into the esophagus, causing inflammation and damage to the esophageal-gastric junction and esophagus
Histological features - characteristics of a given tissue; what the cancerous tissue looks like under a microscope can help define the type of tumor
Poorly differentiated tumor - a tumor made of cells that have lost the features of the tissue from where it arose; often referred to as a 'high-grade' tumor
Prognosis - the likely course of a medical condition
Well-differentiated tumor - a tumor made of cancerous cells that retain the features of stomach cells; often referred to as a 'low-grade' tumor

Etiology

Infectious agents

Infection with Helicobacter pylori is by far the main cause of stomach cancer: nearly 90% of all cases of non-cardia stomach cancer worldwide are attributed to Helicobacter pylori (5). Another infectious agent, the Epstein-Barr virus, might be involved in up to 10% of cases of stomach cancer (6).

Diseases and metabolic disorders

Gastroesophageal reflux disease is a risk factor for cancer arising from the gastric cardia region. Obesity (7-9) and coexisting metabolic disorders (10) have also been associated with stomach cancer.

Unhealthy lifestyles

Unhealthy habits – whether dietary (e.g., high alcohol intake (11), high salt consumption (12, 13), low fiber intake) (14) or non-dietary (e.g., cigarette smoking (15), physical inactivity (16)) – may also contribute to increasing the risk of stomach cancer.

Other risk factors

Other risk factors include age, gender, ethnicity, family history, and socioeconomic status (2, 6).

DEFINITIONS
Gastroesophageal reflux disease - a condition in which the stomach contents, including acid, back up into the esophagus, causing inflammation and damage to the esophageal-gastric junction and esophagus
Obesity - a condition of increased body fat; defined as a body mass index (BMI) ≥30 for adults

Treatment

Late diagnosis has a five-year survival rate of only 20%. Early diagnosis that detects the tumor before it invades the muscular layer of the stomach increases the five-year survival rate to up to 90%. Early-stage gastric cancer can be treated by gastrectomy (via open surgery or laparoscopy) or endoscopic resection of the gastric mucosa. The use of endoscopic treatment or surgery is decided based upon the depth of cancer within the stomach wall.

DEFINITIONS
Endoscopic resection - minimally invasive medical procedure using scopes that go through the oral cavity to reach an early-stage stomach tumor
Gastrectomy - partial or total removal of the stomach by surgery
Laparoscopy - surgery that allows a surgeon to access a tumor within the abdomen without making large incisions in the skin

Nutrition Research

DEFINITIONS
Test tube (in vitro) experiment - a research experiment performed in a test tube, culture dish, or other artificial environment outside of a living organism; in vitro is a Latin phrase meaning 'in glass'
Animal experiment - a research experiment performed in a laboratory animal; many different animal species are studied in the laboratory, including terrestrial (land), aquatic (water), and microscopic animals
Observational study - a human research study in which no experimental intervention or treatment is applied, and participants are simply observed. Observational studies include, among others, case-control and prospective cohort studies. Observational studies can be used to examine whether there may be a relationship between an exposure and an outcome, but they cannot inform whether there is a causal relationship.
Randomized controlled trial - a human research study in which participants are randomly assigned to receive an active treatment or an inert (control or placebo) treatment. Randomized controlled trials are powered to examine whether there is a cause-and-effect relationship between an exposure and an outcome. This type of study is often used to test the efficacy of an active treatment on a specific outcome compared to a control.
Placebo - a substance without therapeutic effect (i.e., a chemically inert substance)
HIGHLIGHT
Test tube experiments are performed on isolated cells, grown in a laboratory, that are often exposed to high concentrations of a test compound. It is important to keep in mind that test tube and animal experiments provide valuable information but differ from human trials in many ways. The outcome may differ for humans ingesting dietary or supplemental versions of the test compound.

Dietary Fat

What it does

General

  • Fat from the diet is a major source of energy for the body, providing 9 calories per gram (g).
  • Types (saturated, monounsaturated, polyunsaturated [including essential], and trans fatty acids) and amounts and types of fat in one's diet have been linked to either possible harms or benefits to health.
  • Dietary recommendations suggest avoiding trans fat, limiting saturated fat (<10% of total energy intake), and replacing saturated fat with mono/polyunsaturated fat (17, 18).

Cancer-specific

  • Free fatty acids influence the ability of tissues to respond to insulin. Increased blood fatty acid concentrations can result in abnormally high concentrations of insulin in blood and contribute to insulin resistance.
  • Animal experiments showed that omega-3 fatty acids (a type of polyunsaturated fatty acids) and their derivatives could reduce the risk of cancer by triggering mechanisms against inflammation, oxidative stress, and abnormal cell proliferation (19).
What we know
  • The risk of developing stomach cancer increases by 8% for each 20-g increase in dietary fat intake per day (20).
  • The risk of stomach cancer is positively associated with the amount of saturated fat in the diet and inversely associated with the amount of polyunsaturated fat in the diet (20).
DEFINITIONS
Insulin resistance - reduced response of tissues to insulin
Inverse association - a relationship between two variables in which they move in opposite directions
Trans fatty acids - trans, unsaturated fatty acids are naturally occurring in small amounts in meat and milk but are produced in large amounts during the industrial processing of vegetable and fish oils. The trans configuration of double bonds in unsaturated fatty acids contrasts with the naturally occurring cis double bonds.

For references and more information, the 2015-2020 Dietary Guidelines for Americans provide detailed advice on fat consumption. Specific recommendations for essential fatty acid (omega-3 and omega-6) intake can also be found in the Essential Fatty Acids article.

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Fiber

What it does

General

  • Fiber is a general term for (mostly) carbohydrates that are resistant to digestion by human enzymes. Fiber may be obtained from food sources, additives, and dietary supplements.
  • As fiber travels through the digestive tract, its physical properties (which vary depending on the type of fiber ingested) impart different health effects.
  • Mechanisms by which fiber may exert health benefits on the gastrointestinal and cardiovascular systems include glycemic control, cholesterol and blood pressure lowering, and regulation of stool consistency and elimination.

Cancer-specific

  • Higher fiber intakes are associated with reduced risks of cancers of the digestive tract (in particular esophageal, gastric, colorectal, and pancreatic cancers), as well as breast cancer and, possibly, ovarian and prostate cancers.
  • Fiber consumption may protect the digestive tract by reducing exposure of the mucosa to carcinogens. Additionally, the fermentation of certain fibers in the large intestine releases short-chain fatty acids that have anticancer activities.
What we know
  • Observational studies have consistently found high intakes of fiber-rich foods to be associated with lower risk of stomach cancer.
HIGHLIGHT

Fiber is identified as a shortfall nutrient of public health concern in the 2015-2020 Dietary Guidelines for Americans

Some suggestions for increasing fiber intake:

  • Eat at least five servings of fruit and vegetables daily.
  • Substitute whole grains for refined grains.
  • Eat oatmeal, whole-grain cereal, or bran cereal for breakfast.
  • Eat beans, split peas, or lentils at least once weekly.
  • Substitute nuts or popcorn for less healthful snacks like potato chips or candy.
DEFINITION
Anticancer activities - a set of actions that contribute to decreasing the chance for abnormal cells to multiply and spread

For references and more information, see the section on cancer prevention in the Fiber article.

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Folate

What it does

General

  • Folate is a B-vitamin that is required for DNA synthesis and the formation of new cells. The vitamin is specifically involved in the synthesis of thymine, an essential DNA component.
  • The B-vitamins folate, riboflavin, vitamin B12, and vitamin B6 work together to convert homocysteine to methionine, an amino acid important for methylation reactions and countless other cellular activities.

Cancer-specific

  • Folate deficiency may increase genomic instability and chromosome breakage, thereby contributing to cancer development.
  • Anti-folate molecules that interfere with DNA synthesis are successfully used in anticancer therapies.
What we know
  • Evidence of a lower risk of stomach cancer with higher intakes of folate from food is limited to case-control studies conducted in the US (21, 22).
HIGHLIGHT
Inadequate folate status in early pregnancy increases the risk of specific birth defects called neural tube defects (NTDs). Since 1998, the US has mandated the fortification of refined grain products with folic acid, which has successfully reduced the occurrence of NTDs. Worldwide, 82 other countries mandate folic acid fortification of at least one refined grain (23).
DEFINITIONS
Methylation reaction - this type of reaction consists of adding a methyl group (-CH3) to a given substrate
Neural tube defects - birth defects arising from the improper closer of the neural tube (the precursor to the brain and spinal cord) of the embryo, which occurs in the 4th week following conception
Thymine - a base that is combined with a sugar and a phosphate group to form one of four building blocks of DNA. The other bases are adenine, guanine, and cytosine. Thymine is replaced by uracil in RNA.

For general information, see the Folate article.

Folate Flashcard. Main Functions: 1) required for DNA synthesis, 2) supports cell growth and repair, 3) helps prevent neural tube defects. Good Sources: legumes (beans, peas, lentils), lentils (cooked) one-half cup = 179 micrograms dietary folate equivalents (DFE); green leafy vegetables (kale, spinach), spinach (cooked) one-half cup, 131 micrograms DFE; fortified food and supplements, sliced bread (enriched), 1 slice, 84 micrograms DFE. Daily Recommendation: 400 micrograms DFE for adults, 600 micrograms DFE for pregnant women. Special Notes: 1) Folate is a general term that refers to both natural folates in food and folic acid, the synthetic form used in supplements and fortified food. 2) DFE = a unit of measure that accounts for differences in the absorption of naturally occurring food folate and synthetic folic acid. 3) To reduce the risk of neural tube defects, all women capable of becoming pregnant should consume 400 micrograms of folic acid daily in addition to the folate obtained from a varied diet. 4) Very high-dose folic acid supplementation (5,000 micrograms) can mask a vitamin B12 deficiency, specifically signs of nerve damage.

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Iron

What it does

General

  • Iron is an essential component of hundreds of essential proteins involved in a wide range of activities, such as oxygen transport and storage, energy metabolism, and DNA synthesis.
  • Some of these proteins, including hemoglobin, cytochromes, and antioxidant enzymes, require iron-containing heme to carry out their biological activities.

Cancer-specific

  • Free (unbound) iron can react with hydrogen peroxide to generate hydroxyl radicals. Iron can also contribute to the formation of nitrosamines. Both types of compounds can damage DNA and increase the risk of cancer.
  • High consumption of heme iron, mainly from red meat, has been associated with a higher risk of colorectal cancer (24).
What we know
  • Limited evidence suggests that high intakes of heme iron might be associated with a higher risk of stomach cancer (25, 26).
DEFINITIONS
Antioxidant enzymes - enzymes which activities contribute to neutralizing atoms or molecules capable of damaging essential cell constituents
Cytochromes - a family of enzymes involved in electron transfer
Hydroxyl radical - a type of reactive oxygen species that can be neutralized by antioxidants
Nitrosamines - cancer-causing compounds produced from nitrites and amines derived from proteins either during meat processing or under the strongly acidic condition of the stomach

For references and more information, see the section on cancer in the Iron article.

Iron Flashcard. Main Functions: 1) Helps make healthy red blood cells that transport oxygen throughout the body, 2) Critical for normal immune function, 3) Structural component of hundreds of essential molecules, and 4) Assists antioxidant enzymes. Good Sources: There are two forms of dietary iron: heme iron and nonheme iron. Heme iron is found in red meat, poultry, and fish. 3 ounces of red meat contains 2.3 mg of heme iron. Nonheme iron is found in lentils, vegetables, and fortified food. One-half cup of cooked lentils contains 3.3 mg of nonheme iron. Daily Recommendation: 8 mg for adult men, 18 mg for women 19-50 years, 8 mg for women 51 years and older. Special Notes: 1) Heme iron is better absorbed than nonheme iron; the absorption of nonheme iron is enhanced by vitamin C. 2) National dietary surveys indicate that iron is underconsumed by adolescent and premenopausal females. 3) The Daily Recommendation for iron is significantly increased during pregnancy (from 18 to 27 mg/day), yet dietary surveys indicate that the average intake among pregnant women in the US is 15 mg/day. 4) Iron is efficiently recycled by the body. Premenopausal women have higher requirements due to menstrual losses.

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Selenium

What it does

General

  • Selenium is an essential trace mineral required for the synthesis of a particular amino acid called selenocysteine.
  • Selenocysteine is a structural component of at least 25 proteins, including enzymes involved in the making of thyroid hormones and of several antioxidant enzymes.

Cancer-specific

  • Deficiency in selenium might compromise antioxidant enzyme activities that protect essential cell constituents against oxidative damage. Oxidative damage to DNA in particular may play a role in the development of cancer.
  • Trials have found no benefit of selenium supplements in the prevention of overall cancer risk or cancer-related mortality. There is also no evidence showing that selenium could lower the risk of specific cancer types (27).
What we know
  • Some, but not all, observational studies reported a lower risk of stomach cancer with higher selenium intakes or higher selenium nutritional status (27-29).
  • One randomized controlled trial in people infected with Helicobacter pylori found no effect of supplementation with selenium, vitamin C, and vitamin E for about seven years on the risk of developing and dying from stomach cancer (30, 31).
DEFINITIONS
Antioxidant enzymes - enzymes which activities contribute to neutralizing atoms or molecules capable of damaging essential cell constituents
Oxidative damage - damage caused to large molecules (i.e., carbohydrates, protein, fat, DNA) by reactive oxygen species

For references and more information, see the section on cancer in the Selenium article.

Selenium Flashcard. Main Functions: (1) Assists antioxidant enzymes, (2) Needed for production of thyroid hormone, which helps maintain body temperature and basal metabolic rate, and (3) Supports immune function. Good Sources: Meat, nuts, seafood, and whole grains are good sources of selenium. Meat (beef, chicken, pork), beef, 3 ounces, 30.6 micrograms; Nuts (Brazil nuts, sunflower seeds), sunflower sees, one-fourth cup, 18.6 micrograms; Seafood (tuna, clams, shrimp), tuna, 3 ounces, 92.0 micrograms. Daily Recommendation: 55 micrograms for adults. Special Notes: (1) The selenium content of plants and grains varies greatly. (a) Food selenium content is influenced by the selenium content of the soil in which it was grown. (b) Some plants accumulate selenium to a greater extent, including garlic, Brazil nuts, and Brassica vegetables (broccoli, Brussel sprouts, cabbage, cauliflower, kale). (c) A single serving of Brazil nuts (6 nuts) is above the tolerable upper intake level (UL) of 400 micrograms per day. (2) Most people in the US consume enough selenium to meet the recommendation.

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Sodium Chloride

What it does

General

  • Sodium and chloride are electrolytes working together to control fluid volume, blood pressure, acid-base homeostasis, and membrane potential, thereby supporting normal physiological functions.
  • Excess intake of salt (sodium chloride) affects the normal functioning of blood vessels, causing high blood pressure and cardiovascular disease.
  • Excess sodium can also be harmful to bone health in older women, especially when their calcium intakes are low.

Cancer-specific

  • Animal studies suggested that high intakes of salt may damage the cells lining the stomach and increase the risk of infection by Helicobacter pylori.
  • The cancer-causing effect of nitrosamines present in salty foods like processed and cured meats or fish may be further enhanced by salt.
What we know
  • High salt consumption is associated with a higher risk of developing stomach cancer (12, 13).
  • Health policies aiming to reduce salt consumption are effective to save lives that would be lost to stomach cancer (32).
  • Striving to reduce salt intake to the recommended levels lower one's risk for stomach cancer.
DEFINITIONS
Electrolytes - charged particles (called ions) that are constituents of all living cells and tissues. Major electrolytes in the body include sodium, potassium, magnesium, calcium, chloride, bicarbonate, and phosphate.
Homeostasis - refers to a state of equilibrium in biological systems. Dynamic mechanisms deal with changes in internal and external environments to ensure constancy of physiological conditions.
Nitrosamines - cancer-causing compounds produced from nitrites and amines derived from proteins either during meat processing or under the strongly acidic condition of the stomach

For references and more information, see the section on gastric cancer in the Sodium article.

Sodium Flashcard. Main Functions: (1) Maintains fluid and electrolyte balance. (2) Required for proper nerve conduction and muscle contraction. (3) Influences blood volume and blood pressure. Good Sources: Most dietary sodium comes from processed and restaurant food. Processed Foods (canned foods, lunch meat, potato chips), chicken noodle soup, canned, 1 cup, 789 mg; ham, minced, 3 ounces, 1,059 mg. Table Salt (sodium chloride): table salt, 1 teaspoon, 2,325 mg. Daily Recommendation: 1,500 mg for adults 19-50 years, 1,300 mg for adults 51-70 years, and 1,200 mg for adults 71 years and older. Special Notes: Most people consume too much sodium! (1) Diets low in sodium and high in potassium reduce fluid retention and favorably affect blood pressure. (a) Consuming 1,200 mg of sodium per day or less is associated with significant blood pressure reduction. (b) Fruit, vegetables, and legumes are naturally low in sodium and high in potassium.

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Vitamin A

What it does

General

  • Vitamin A refers to a number of fat-soluble vitamins (collectively known as retinoids) involved in the growth and differentiation of virtually all cells in the body.
  • Vitamin A is essential for normal vision, reproduction, development, and immune function.
  • Retinol is a ready-to-use form of vitamin A present in the body, as well as in foods of animal origin. β-Carotene and other carotenoids in plants can be converted (to some extent) into retinol by the body (see Carotenoids below).

Cancer-specific

  • Test tube and animal experiments showed that all-trans retinoic acid — a biologically active form of vitamin A — can stop the multiplication and spread of cancer cells and trigger their death (33).
  • Several retinoids are approved for the treatment of cancers, such as neuroblastoma and certain lymphomas (34).
What we know
  • Habitual high dietary intakes of vitamin A may be associated with a lower risk of stomach cancer (35).
  • Use of vitamins from supplements has been associated with a lower risk of stomach cancer only with doses below the tolerable upper intake level (UL) (36).
HIGHLIGHT
Consumption of high doses of vitamin A (in the form of retinol or retinyl esters) can be highly toxic and is unlikely to reduce the risk of stomach cancer. Vitamin A supplements should be reserved for undernourished populations and individuals with evidence of vitamin A deficiency.
DEFINITIONS
Lymphomas - a group of blood cancers developing from specific white blood cells called lymphocytes
Neuroblastoma - cancer arising from nerve cells of the central or peripheral nervous system
Tolerable upper intake level (UL) - the highest level of daily intake of a given nutrient that likely poses no risk of adverse effects in almost all individuals of a specified age. The UL for vitamin A in adults is set at 3 mg/day of retinol equivalents (10,000 IU/day).

For more information on vitamin A, see the Vitamin A article.

Vitamin A (retinol) Flashcard. Main Functions: 1) Essential for site, dim-light adaptation, and color vision; 2) Supports reproductive health for both men and women; 3) Required for proper immune function; 4) Influences cell growth and development. Good Sources: There are two forms of dietary vitamin A: preformed vitamin A from animal products and provitamin A carotenoids from fruit and vegetables. Preformed Vitamin A: cod liver oil, 1 teaspoon = 1,350 micrograms retinol activity equivalents (RAE), 1 large egg = 80 micrograms RAE. Provitamin A (yellow & orange fruit & vegetables), sweet potato (baked), 1 cup = 1,922 micrograms RAE. Daily Recommendation: 900 micrograms RAE for men and 700 micrograms RAE for women. Special Notes: 1) RAE = a unit of measure for the vitamin A content of food. It reflects the amount of active vitamin A provided by the different types of food sources. 2) It is possible to ingest too much vitamin A (retinol). The Tolerable Upper Intake Level (UL) is 3,000 micrograms RAE of retinol/day. 3) There is no UL for provitamin A carotenoids because the liver controls their conversion to retinol.

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Vitamin B12

What it does

General

  • Vitamin B12 helps convert food to useable energy and is required for proper nerve function.
  • Untreated vitamin B12 deficiency can lead to irreversible nerve damage.

Cancer-specific

  • Along with other B-vitamins, vitamin B12 is needed for the synthesis of methionine, an amino acid important for methylation reactions. Abnormal methylation of DNA and proteins is linked to genomic instability, chromosome breakage, and alterations in gene expression, all contributing to cancer development.
What we know
  • Atrophic gastritis induced by Helicobacter pylori infection damages the lining of the stomach, causing a reduction in acid secretion and intrinsic factor, a glycoprotein that is necessary for the absorption of vitamin B12. Thus, atrophic gastritis may result in vitamin B12 deficiency.
  • Atrophic gastritis may progress to stomach cancer. Low vitamin B12 status is thus not uncommon in people with stomach cancer (37).
DEFINITIONS
Atrophic gastritis - chronic inflammation of the stomach lining with glandular cells being replaced by intestinal and fibrous tissues
Methylation reaction - this type of reaction consists of adding a methyl group (-CH3) to a given substrate

For references and more information, see the Vitamin B12 article.

Vitamin B12 (cobalamin) Flashcard. Main Functions: 1) Helps make red blood cells, 2) Required for proper nerve function, and 3) Helps maintain normal levels of homocysteine in the blood. Good Sources: Vitamin B12 is only found in animal products. Seafood (shellfish, fish), clams (steamed) 3 ounces = 84 micrograms; poultry (turkey, chicken, duck), roasted turkey, 3 ounces = 0.8 micrograms; red meat (beef, pork, lamb), lean beef plate steak (grilled), 3 ounces = 6.9 micrograms. Daily Recommendation: adults 19-50 years = 2.4 micrograms; LPI recommends older adults (51 years and older) take 100-400 micrograms of supplemental vitamin B12. Special Notes: 1) Over-the-counter antacids reduce vitamin B12 absorption. 2) The capacity to absorb vitamin B12 from food goes down with age. 3) Symptoms of vitamin B12 deficiency include tingling and numbness in the extremities, nerve damage, and memory loss. 4) Older adults and individuals consuming a vegan diet should obtain vitamin B12 from supplements or fortified food.

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Vitamin C

What it does

General

  • Vitamin C (ascorbic acid) is a water-soluble vitamin that neutralizes a variety of reactive oxygen species and recycles important cellular antioxidants (including vitamin E).
  • Vitamin C is also a cofactor in enzymatic reactions involved in the regulation of gene expression and in the making of collagen, L-carnitine, and several neurotransmitters.

Cancer-specific

  • Vitamin C is a cofactor to enzymes that influence the methylation of DNA. DNA methylation plays a crucial role in the stability of the genome; alterations of the DNA methylation profile are a feature of cancer development.
  • Vitamin C might lower the risk of stomach cancer by scavenging reactive oxygen species, thereby protecting the stomach lining from oxidative damage, and by limiting the formation of nitrosamines in the stomach (38).
What we know
  • A recent pooled analysis of 12 observational studies found a 26% lower risk of stomach cancer with daily intakes of 100 mg of vitamin C (36).
  • Several recent trials suggest that vitamin C may be a useful adjunct to standard treatment against Helicobacter pylori infection, thereby potentially contributing to lower the risk of developing stomach cancer (39).
DEFINITIONS
Adjunct therapy - also called add-on therapy; refers to a treatment that is given in addition to the standard-of-care in order to enhance efficacy of treatment
Nitrosamines - cancer-causing compounds produced from nitrites and amines derived from proteins either during meat processing or under the strongly acidic condition of the stomach
Oxidative damage - damage caused to large molecules (i.e., carbohydrates, protein, fat, DNA) by reactive oxygen species
Reactive oxygen species - highly reactive atoms or molecules produced by normal cellular metabolism and certain environmental factors. If not neutralized by antioxidants, they can damage large molecules (i.e., DNA, carbohydrates, lipids, proteins) and alter their function

For references and more information, see the section on stomach cancer in the Vitamin C article.

Vitamin C (ascorbic acid) Flashcard. Main Functions: 1) Antioxidant defense, 2) Enhances immune function, 3) Needed to make collagen, carnitine, and the neurotransmitters serotonin and norepinephrine. Good Sources: Fruit, 1 medium-sized kiwifruit = 90 mg; strawberries, 1 cup whole, 85 mg; Vegetables (broccoli, kale, tomatoes), sweet red pepper (one-half cup, chopped) = 95 mg. Daily Recommendation is 400 mg for all adults. Special Notes: 1) Heat destroys vitamin C. Try to eat fresh foods and cook by steaming, microwaving, or stir-frying. 2) Vitamin C in food is identical to vitamin C in supplements. 3) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 90 mg/day for men and 75 mg/day for women.

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Vitamin D

What it does

General

  • Vitamin D is made in the skin upon sunlight (UV) exposure and can also be obtained from a few foods or supplements.
  • Vitamin D is a fat-soluble vitamin that helps to regulate calcium and phosphorus homeostasis, promotes bone health and immune function, and influences cell growth and development.

Cancer-specific

  • Test tube and animal experiments showed that vitamin D can stop the multiplication and trigger the death of various types of cancer cells.
  • Low blood vitamin D has been associated with a higher risk of dying prematurely of cancer.
What we know
  • At the population level, there are associations between levels of UV irradiance, vitamin D sufficiency, and survival from stomach cancer (40).
  • At the individual level, neither vitamin D status nor vitamin D intake is associated with the risk of stomach cancer (36, 41).
DEFINITION
Homeostasis - a state of equilibrium in biological systems. Dynamic mechanisms deal with changes in internal and external environments to ensure constancy of physiological conditions.

For general information on vitamin D, see the Vitamin D article.

Vitamin D (calciferol) Flashcard. Main Functions: 1) Facilitates absorption of calcium and phosphorus, 2) Promotes bone health, 3) Required for proper immune function, and 4) Influences cell growth and development. Good Sources: Fatty Fish (salmon, mackerel, sardines), pink canned salmon, 3 ounces = 465 IU or 11.6 micrograms; Canned mackerel, 3 ounces = 211 IU for 5.3 micrograms; Fortified food, low-fat milk, vitamin D fortified, 8 ounces = 98 IU or 2.5 micrograms. Daily Recommendation: 600-1,000 IU (15-25 micrograms) for chldren and adolesents (4-18 years), because vitamin D is scarcely found in food, it may be necessary to take supplements. 2,000 IU or 50 micrograms for all adults, this amount applies to supplemental vitamin D, which is recommended in addition to vitamin D from a mixed diet. Special Notes: 1) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 600 IU (15 micrograms)/day for males and females who are 4-70 years old, and 800 IU (20 micrograms)/day for all adults over 70. 2) Vitamin D is considered a "Nutrient of Public Health Concern" because underconsumption is linked to adverse health outcomes. 3) More than 90% of Americans do not meet the dietary requirement for vitamin D. 4) our bodies make vitamin D upon skin exposure to UVB radiation from the sun. Darker skin color, northern latitude, and older age impede the amount of vitamin D produced.

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Vitamin E

What it does

General

  • Vitamin E is a fat-soluble vitamin that functions as an antioxidant in lipid environments.
  • Vitamin E augments the functional activity of immune cells by protecting their cell membranes from oxidative damage.

Cancer-specific

  • Oxidative damage to DNA in particular may play a role in the development of cancer. By neutralizing free radicals, vitamin E may prevent damage to all major cell components, including DNA.
  • In most trials, supplementation with vitamin E has failed to reduce the risk of developing cancer.
  • People at risk of lung cancer, including smokers, should get vitamin E preferably from food sources rather than supplements to avoid unintended side effects.
What we know
  • Higher intakes of vitamin E from food have been associated with a lower risk of developing stomach cancer (36, 42).
  • In contrast, blood vitamin E concentration does not appear to be associated with the risk of stomach cancer (42).
  • No trial has yet shown that vitamin E supplements could be helpful to prevent or treat stomach cancer.
DEFINITIONS
Free radicals - atoms or molecules (with ≥1 unpaired electron) that are highly reactive and can potentially damage large molecules like DNA and lipids; e.g., reactive oxygen species
Oxidative damage - damage caused to large molecules (i.e., carbohydrates, protein, fat, DNA) by reactive oxygen species

Vitamin E (alpha-tocopherol) Flashcard. Main Functions: 1) Boosts antioxidant defense, 2) Protects cell membranes, and 3) Enhances immune function. Good Sources: vegetable oil, sunflower oil (1 tablespoon), 5.6 mg; nuts (hazelnuts, peanuts), almonds, 1 ounce or 23 almonds, 7.3 mg; avocado, 1 medium-sized, 2.7 mg. Daily Recommendation is 15 mg for all adults. Special Notes: 1) The term "vitamin E" actually refers to a family of eight coupounds. Alpha-tocopherol is the most active vitamin E compound. 2) More than 90% of Americans do not meet the dietary requirement for vitmain E. 3) Synthetic vitamin E (in supplements and fortified food) is less bioavailable than naturally occurring vitamin E from food.

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Carotenoids

What it does

General

  • Carotenoids are yellow, orange, and red pigments found in fruit and vegetables. We can distinguish:
    • Those which the body can use to form vitamin A, i.e., α-carotene, β-carotene, and β-cryptoxanthin;
    • Those which cannot be converted to vitamin A, i.e., lutein, zeaxanthin, and lycopene.
  • Lutein and zeaxanthin can protect specialized cells in the retina against oxidative damage.
  • Supplementation with lutein and zeaxanthin may help slow down the progression of age-related macular degeneration in affected people, especially if their carotenoid intake from food is low.

Cancer-specific

  • Carotenoids have demonstrated anticancer activities in test tube experiments (43).
  • Supplementation with β-carotene has not resulted in a reduction in overall cancer risk (44).
  • People at risk for lung cancer, including smokers, are advised against the use of β-carotene supplements (44).
What we know
  • Prospective cohort studies found no association between high intakes of carotenoid-rich fruit and vegetables and the risk of stomach cancer (45).
  • Regular intake of β-carotene supplements at doses ≥20 mg/day for many years may increase the risk of stomach cancer, especially in smokers (44).
DEFINITIONS
Anticancer activities - a set of actions that contribute to decreasing the chance for abnormal cells to multiply and spread
Age-related macular degeneration - a disease that affects vision and can lead to blindness
Oxidative damage - damage caused to large molecules (i.e., carbohydrates, protein, fat, DNA) by reactive oxygen species

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Curcumin

What it does

General

  • Curcumin is a naturally occurring plant chemical that is abundant in the spice turmeric.
  • Experiments performed in test tubes indicated that curcumin can trigger antioxidant and anti-inflammatory defense systems within cells.
  • Animal experiments showed a protective effect of curcumin against stress-induced ulcers and other lesions of the gastric mucosa caused by the chronic use of drugs (e.g., NSAIDs) (46).

Cancer-specific

  • The results of pilot studies suggest that high doses of oral curcumin might help improve tumor-related markers and provide symptomatic relief in patients with cancer (47).
  • The therapeutic efficacy of oral curcumin administration depends on the bioavailability of curcumin, which is very low since curcumin is readily excreted by the body upon absorption. Innovative solutions are being developed to improve curcumin bioavailability (48).
What we know
  • The use of curcumin as an adjunct to standard treatment was shown to relieve symptoms in patients with Helicobacter pylori-induced gastritis (49-51).
  • No human study has yet examined curcumin intakes from food or supplements in relation to the risk of stomach cancer.
DEFINITIONS
Adjunct therapy - also called add-on therapy; refers to a treatment that is given in addition to the standard-of-care in order to enhance efficacy of treatment
Bioavailability - the fraction of ingested compound that reaches the circulation and is transported to the site of action
NSAIDs - acronym for nonsteroidal anti-inflammatory drugs; NSAIDs reduce pain and inflammation and are prescribed for the symptomatic relief of people affected by chronic inflammatory conditions.
Pilot study - a preliminary study performed to test specific parameters and decide whether a research project could be scaled up

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Flavonoids

What they do

General

  • Flavonoids are plant chemicals that belong to a class of compounds called phenols.
  • Six major subclasses of flavonoids are widely found in edible plants: anthocyanidins, flavan-3-ols, flavonols, flavones, flavanones, and isoflavones.
  • High intakes of flavonoid-rich foods are associated with a 26% lower risk of premature death (52).

Cancer-specific

  • Many of the biological effects of flavonoids are related to their ability to modulate signaling pathways inside of cells. In test tube and animal experiments:
    • Flavonoids showed anticancer activities, including abilities to scavenge free radicals, trigger carcinogen excretion, and prevent the multiplication and spread of abnormal cells.
    • Some flavonols, namely kaempferol and quercetin, have also displayed anti-Helicobacter pylori activities (53).
What we know
  • There is little evidence to suggest that high intakes of flavonoid-rich food and beverages are associated with a lower risk of developing stomach cancer (54-58).
  • No trials have explored the potential benefits of flavonoids for the prevention or treatment of stomach cancer.
DEFINITIONS
Carcinogen - cancer-causing agent
Free radicals - atoms or molecules (with ≥1 unpaired electron) that are highly reactive and can potentially damage large molecules like DNA and lipids; e.g., reactive oxygen species
Signaling pathway - refers to a cascade of events leading to changes within a cell in response to changes in a cell's environment

For more information, see the section on cancer prevention in the Flavonoids article.

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Isothiocyanates

What they do

General

  • Isothiocyanates are compounds formed from glucosinolates found in cruciferous vegetables (e.g., Brussels sprouts, kale, broccoli, bok choy).
  • Most prominent isothiocyanates include benzyl isothiocyanate, phenethyl isothiocyanate, and sulforaphane.

Cancer-specific

  • The biological effects of isothiocyanates are related to their ability to modulate signaling pathways inside of cells.
  • In test tube and animal experiments (59, 60):
    • Isothiocyanates could limit the multiplication of Helicobacter pylori and mitigate Helicobacter pylori-induced stomach inflammation;
    • Isothiocyanates could help eliminate carcinogens, protect cells/tissues from oxidative damage, and prevent the multiplication and spread of cancerous cells.
What we know
  • High intakes of cruciferous vegetables are associated with a lower risk of developing stomach cancer (61).
  • Evidence from pilot studies is currently too limited to say whether supplementation with isothiocyanates can help control Helicobacter pylori infection in humans (60, 62, 63).
DEFINITIONS
Carcinogen - cancer-causing agent
Glucosinolates - sulfur-containing compounds present in cruciferous vegetables. When raw cruciferous vegetables are chopped, the breakdown of glucosinolates releases isothiocyanates.
Oxidative damage - damage caused to large molecules (i.e., carbohydrates, protein, fat, DNA) by reactive oxygen species
Pilot study - a preliminary study performed to test specific parameters and decide whether a research project could be scaled up
Signaling pathway - refers to a cascade of events leading to changes within a cell in response to changes in a cell's environment
HIGHLIGHT
Cruciferous vegetables are usually cooked before consumption such that only a small fraction of glucosinolates is broken down to release isothiocyanates. Chop raw cruciferous vegetables and let them sit for several minutes to maximize the formation of isothiocyanates prior to cooking. It is best to lightly steam cruciferous vegetables for no more than five minutes.

For more information, read the articles on Isothiocyanates and Cruciferous Vegetables.

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Alcoholic Beverages

What they do

General

  • Alcoholic beverages contain ethanol and other ingredients with bioactive properties and health effects.
  • When consumed in moderation (1-2 drinks/day), alcohol has been associated with beneficial effects on the cardiovascular system.

Cancer-specific

  • Even modest intakes of alcohol may increase the risk of cancer (64).
  • Alcohol intake is a risk factor for several cancer types, including cancers of the oral cavity, pharynx, larynx, esophagus, colorectum, breast, and liver (64, 65).
What we know
  • There is no consistent evidence to suggest a higher risk of stomach cancer with regular intakes of ≤1 alcoholic drink/day (66, 67).
  • Regular intakes of >1 alcoholic drink/day (>24 g/day) are associated with a higher risk of stomach cancer (66, 67).
    • There is a 7% increase in stomach cancer risk for each 10 g/day increment in alcohol consumption (11).
HIGHLIGHT
  • 1 standard alcoholic drink contains 14 g of pure alcohol, which is equivalent to:
    • 12 fluid ounces (fl oz) of beer (~5% of alcohol);
    • 8.5 fl oz of malt liquor (~9% of alcohol);
    • 5 fl oz of wine (~12% of alcohol);
    • 1.5 fl oz of distilled spirit (liquors; ~40% of alcohol)
  • Alcohol is metabolized differently in women and men such that recommendations have a lower threshold for women
  • No alcohol should be consumed by:
    • Pregnant women or women intending to become pregnant;
    • People taking over-the-counter or prescribed medications with the potential for adverse interactions with alcohol;
    • People planning to drive or engage in activities requiring coordination and alertness;
    • Recovering alcoholics;
    • Anyone aged <21 years (according to US alcohol legislation).

For more information, read the article on Alcoholic Beverages.

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Coffee

What it does

General

  • Coffee is a complex mixture of carbohydrates, lipids, amino acids, minerals, and other bioactive compounds like caffeine that can influence human health.
  • Drinking coffee is associated with a lower risk of developing type 2 diabetes mellitus and a lower risk of dying from cardiovascular disease.

Cancer-specific

  • Some bioactive compounds present in coffee, such as caffeine and a class of phytochemicals called diterpenes, have displayed anticancer activities in experimental studies (68).
  • Lower risks of cancer of the oral cavity, uterus, and liver have been consistently reported in coffee drinkers (68, 69).
  • There is no relationship between coffee consumption and death from cancer overall (69).
What we know
  • There is no evidence from observational studies of a reduced risk of gastric cancer with coffee consumption. A higher risk reported in some studies is likely due to residual confounding by factors such as alcohol intake, cigarette smoking, or obesity.
  • Consuming ≤3 cups of filtered coffee daily is unlikely to pose any risk to health. Pregnant women are generally advised to limit caffeinated coffee intake to 1 cup daily.
DEFINITIONS
Anticancer activities - a set of actions that contribute to decreasing the chance for abnormal cells to multiply and spread
Confounder - an extraneous factor in an observational study that distorts or biases an association between an exposure and the measured outcome. Confounders are associated with the exposure and outcome of interest, but they are not in the causal pathway.
Phytochemicals - biologically active molecules found in plants
Residual confounding - results when investigators fail to completely control for confounders by adjustment in statistical analyses

For more information, see the section on cancer prevention in the Coffee article.

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Dairy Products

What they do

General

  • Dairy products refer to milk and products derived from milk like yogurt and cheese. Dairy foods are a good source of energy (protein, fat, carbohydrates), vitamins (e.g., B vitamins, vitamin D [when fortified]), and minerals (e.g., calcium, magnesium, phosphorus, potassium, sodium, zinc) (70).
  • Dairy consumption plays an important role for bone health across all stages of life by supplying key nutrients (especially calcium, vitamin D, and protein) necessary to build strong bones and limit the occurrence of bone disease and fractures later in life (71).
  • Consumption of dairy products is associated with a lower risk of type 2 diabetes mellitus (72, 73). Recent analyses have found no such associations with risks of hypertension (74) or cardiovascular disease (75, 76).
HIGHLIGHT
Replacing dairy products by calcium replacement foods (e.g., bony fish, calcium-set tofu, leafy greens, and fortified beverages [e.g., soy- or almond-based beverages, rice drink, orange juice]) alter the nutritional profile of one's diet. For example, substituting soy drinks for low-fat dairy will supply less protein, fat, magnesium, phosphorus, and potassium (77).

Cancer-specific

  • Dairy products are a major source of conjugated linoleic acid, which has been found to display anticancer activities in experimental studies. The overall nutritional profile of dairy foods may also be important to protect against cancer (70).
  • Dairy food consumption has been associated with a lower risk of colorectal cancer (78) but not of other cancer types like lung (79, 80), pancreatic (81), breast (82, 83), and endometrial (84) cancers.
  • Consumption of dairy products, especially whole milk, has been associated with potentially higher risks of prostate cancer (85), ovarian cancer (86), and non-Hodgkin lymphoma (87).
What we know
  • Some evidence points to an increased risk of gastric cancer with higher consumption of milk but not of total dairy or cheese (88). However, no causal relationship has been established.
  • It is suggested that certain compounds in feedstuffs consumed by dairy animals may be passed into milk and be carcinogenic to humans (89).
HIGHLIGHT
Most recommended healthy dietary patterns include the consumption of three servings of dairy foods per day in order to meet the recommended dietary allowance (RDA) for calcium (17, 90). The 2015-2020 Dietary Guidelines for Americans recommend to choose fat-free or low-fat dairy alternatives (17), although be aware that fat may be replaced by sugars in some of these products.
DEFINITIONS
Anticancer activities - a set of actions that contribute to decreasing the chance for abnormal cells to multiply and spread
Carcinogenic - refers to a compound that has the potential to cause cancer
Recommended Dietary Allowance (RDA) - the average daily dietary intake level of a nutrient sufficient to meet the requirements of nearly all healthy individuals in a specific life stage and gender group

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Fruit and Vegetables

What they do

General

  • Adherence to diets rich in fruit and vegetables has consistently been associated with lower risks of developing chronic disease, particularly type 2 diabetes mellitus and cardiovascular disease.
  • Higher intakes of apples, berries, citrus fruit, cruciferous vegetables, and green leafy vegetables have been associated with a lower risk of dying prematurely.

Cancer-specific

  • Daily consumption of five portions (~400 g) of a variety of fruit and non-starchy vegetables is recommended to lower the risk of certain types of cancer (91).
  • Micronutrients (e.g., vitamin C) and phytochemicals (e.g., flavonoids in citrus fruit, organosulfur compounds in garlic and cruciferous vegetables) have anticancer properties likely related to their ability to limit carcinogen formation, activation, and/or toxicity, and to prevent abnormal cell multiplication.
  • Fruit and vegetables are also a great source of dietary fibers that protect the digestive mucosa from exposure to carcinogens and contribute, through their fermentation in the colon, to the formation of short-chain fatty acids with anti-inflammatory and anticancer activities.
What we know
  • High intakes of cruciferous vegetables (61) are associated with a lower risk of developing stomach cancer. There is limited evidence of an association between intake of garlic (92, 93) or citrus fruit (38, 94) and risk of stomach cancer.
  • Interventions that used garlic preparations found no evidence of benefit in either gastric cancer prevention or treatment of Helicobacter pylori infection.
HIGHLIGHT
Several initiatives and resources, including Fruits & Veggies for Better Health, ChooseMyPlate, 2015-2020 Dietary Guidelines for Americans, and the Intake Recommendations section of the article on Fruit and Vegetables, have been developed to help people include more fruit and vegetables in their daily meals and, more generally, to help people make healthier food choices.
DEFINITIONS
Carcinogen - a cancer-causing compound
Flavonoids - phenolic compounds widely found in fruit and vegetables — citrus fruit (e.g., oranges, lemons, grapefruit) are rich in a subclass of flavonoids called flavanones
Organosulfur compounds - sulfur-containing molecules. The two main classes of organosulfur compounds found in whole garlic cloves are called L-cysteine sulfoxides and γ-glutamyl-L-cysteine peptides. Organosulfur compounds found in cruciferous vegetables are called isothiocyanates.
Phytochemicals - biologically active molecules found in plants

For references and more information, read the articles on Fruit and Vegetables, Cruciferous Vegetables, and Garlic.

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Mediterranean Diet

What it does

General

  • The traditional Mediterranean diet is characterized by a high intake of olive oil, nuts, fruit, vegetables, and cereal; moderate intake of fish and poultry, dairy products, eggs, and alcohol; and low intake of red and processed meats.
  • Adherence to the Mediterranean diet is associated with reduced risks of cardiovascular disease and overall mortality (95).

Cancer-specific

  • The Mediterranean diet has been traditionally associated with a protective effect against cancer (96-98).
What we know
  • High adherence to the Mediterranean diet has been associated with a 33% lower risk of developing stomach cancer in a large European multicenter prospective cohort study (99).
  • It is unclear whether the potential protective effect of adopting a Mediterranean diet could help prevent all types of stomach cancer (99-101).
HIGHLIGHT
Appendix 4 of the 2015-2020 Dietary Guidelines for Americans provides recommended amounts of foods from each food group for people who want to follow a healthy Mediterranean-style diet.

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Nuts

What they do

General

  • Nuts are a good source of soluble fiber, phytosterols, polyphenols, mono- and polyunsaturated fatty acids, protein, vitamins (folate, vitamin E), and minerals (calcium, magnesium, potassium).
  • Examples of tree nuts include almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios, and walnuts.
  • Peanuts are not nuts; they are legumes. However, peanuts and tree nuts have a similar content of nutrients and thus share some benefits to health.
  • Regular nut consumption (1 ounce at least 5 times per week) is associated with a significantly lower risk of developing or dying from coronary heart disease.

Cancer-specific

  • Several nutritional components present in nuts and peanuts — fiber (102), phytochemicals (103-107), micronutrients (108), and mono/polyunsaturated fatty acids (109) — may protect against cancer.
  • Nut consumption has been inversely associated with the risk of certain cancer types, including colorectal cancer, ovarian cancer, and prostate cancer (110), and with the risk of premature death by cancer (111).
What we know
  • Two large prospective cohorts found an inverse association between tree nut and peanut consumption and the risk of non-cardia gastric adenocarcinoma. In contrast, consumers and non-consumers of nuts had a similar risk of developing cardia adenocarcinoma (112, 113).
  • It is not known whether substituting dietary saturated fat with unsaturated fat (from nuts in particular) could reduce the risk of non-cardia adenocarcinoma.
HIGHLIGHT
  • Nuts are packed with healthy fats, and therefore, calories.
    • 1 ounce of nuts contains approximately 160 kcal and 14-19 g of fat (mainly mono- and polyunsaturated fatty acids)
  • 1 ounce of nuts equals approximately: 24 almonds, 8 medium Brazil nuts*, 18 medium cashews, 12 hazelnuts, 12 macadamia nuts, 15 pecan halves, 47 pistachios, 14 walnut halves, and 35 peanuts.
  • It is recommended to substitute nuts for sources of saturated fat and junk food.

*Depending on growth conditions, a single Brazil nut could contain an extremely high amount of selenium.

DEFINITIONS
Coronary heart disease - refers to a condition caused by the buildup of fat within the walls of coronary arteries that limits blood supply (and thus oxygen supply) to the heart
Inverse association - a relationship between two variables in which they move in opposite directions
Phytochemicals - biologically active molecules found in plants

For more information, see the articles on Nuts and Essential Fatty Acids.

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Red and Processed Meats

What they do

General

  • Meat is a good source of protein, vitamins (vitamin A and B vitamins), and minerals (iron, zinc, selenium, phosphorus). The fat content of meat varies across retail cuts of beef, poultry, and other meats, as well as with processing techniques and cooking methods (114).
  • Red meat refers to meat of beef, veal, pork, lamb, sheep, horse, and goat. Processed meat usually refers to red meat-derived products that are cured, salted, or smoked, and contain high amounts of minced fatty tissues (e.g., sausages) (115). Thus, processed meat usually has a higher content of saturated fat, cholesterol, salt (sodium chloride), and nitrates than fresh, unprocessed red meat (116).
  • Long-term consumption of red meat, especially if processed, has been associated with higher risks of type 2 diabetes mellitus, cardiovascular disease, and premature death (116).

Cancer-specific

  • Several molecules generated during meat processing (e.g., N-nitroso-compounds, polycyclic aromatic hydrocarbons) or when meat is heated at high temperatures (e.g., heterocyclic aromatic amines) are suspected or well-known carcinogens. Other mechanisms involving, for example, the oncogenic effect of heme iron (much more abundant in red than white meat) have been suggested to explain the potential hazards associated with consuming red and processed meats (116).
  • High consumption of red and processed meats is a recognized risk factor for colorectal cancer (117). More limited evidence suggests that consuming large amounts of red and/or processed meat is associated with higher risks of esophageal, liver, and bladder cancer (115, 116).
HIGHLIGHT
The International Agency for Research on Cancer (IARC) identified red meat and processed meats as (potential) carcinogenic hazards to humans. See the IARC monographs on red meat and processed meat.
What we know
  • Pooled results from prospective cohort studies found no association between intakes of red/processed meat and risk of developing stomach cancer (118).
  • Large intakes of meat might increase the risk of stomach cancer in certain individuals who are already susceptible to developing stomach cancer because, for example, they are genetically predisposed or they are infected by Helicobacter pylori (116).
HIGHLIGHT

Reducing the consumption of red and processed meat in high-consuming countries is generally recommended for both environmental and health concerns. Guidelines from the American Cancer Society suggest to reduce red and processed meat consumption by (119):

  • Limiting the consumption of bacon, sausage, luncheon meats, and hot dogs
  • Choosing fish, poultry, or beans as an alternative to red meat
  • Opting for lean cuts and eating smaller portions of red meat
  • Preparing meat, poultry, and fish by baking, broiling, or poaching rather than frying or charbroiling
DEFINITIONS
Carcinogen - cancer-causing agent
Genetically predisposed - refers here to individuals whose variations in the sequence of genes coding for enzymes that are involved in metabolizing and/or detoxifying carcinogens may increase the cancer-causing potential of certain compounds present in red/processed meat
Oncogenic effect - ability to cause the development of a tumor

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Tea

What it does

General

  • Tea is an infusion of the leaves of the Camellia sinensis plant and includes white, green, oolong, and black teas. Herbal "teas" are infusions of herbs or plants other than Camellia sinensis.
  • Tea contains a number of bioactive substances, including caffeine, fluoride, and flavonoids (primarily flavan-3-ols), which may exert health effects. Daily consumption of 2 to 4 cups of tea is associated with lower risks of type 2 diabetes mellitus and cardiovascular disease (120).

Cancer-specific

  • Tea is particularly rich in catechins (flavan-3-ol monomers), a subclass of flavonoids with antioxidant activities that could protect in particular the epithelium of the digestive tract against oxidative injury, block the activation of carcinogen, and interfere with cancer cell multiplication (121).
  • Tea consumption has not been associated with lower risks of any cancer types except cancers of the oral cavity (122).
What we know
  • There is no consistent evidence to suggest that higher intakes of tea are associated with a reduced risk of developing stomach cancer (122, 123).
  • Consuming very hot beverages (including very hot tea, i.e., >65°C or >149°F) may damage the cells lining the upper digestive tract and specifically increase the risk of esophageal (124) and stomach (123) cancers.
DEFINITION
Antioxidant activities - a set of actions that contribute to prevent damage caused to cell constituents by the presence of highly reactive atoms or molecules (e.g., reactive oxygen species)

For more information on tea and cancer prevention, see the section in the Tea article.

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