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Despite all of the controversy surrounding the optimal components of a healthy diet, there is little disagreement among scientists regarding the importance of fruits and vegetables. The results of numerous epidemiological studies and recent clinical trials provide consistent evidence that diets rich in fruits and vegetables can reduce the risk of chronic disease (1). On the other hand, evidence that very high doses of individual micronutrients or phytochemicals found in fruits and vegetables can do the same is inconsistent and relatively weak. Fruits and vegetables contain thousands of biologically active phytochemicals that are likely to interact in a number of ways to prevent disease and promote health (2). Fruits and vegetables are rich in antioxidants, which help protect the body from oxidative damage induced by pro-oxidants. The best way to take advantage of these complex interactions is to eat a variety of fruits and vegetables.
Dietary patterns characterized by relatively high intakes of fruits and vegetables are consistently associated with significant reductions in the risk of coronary heart disease (CHD) and stroke. A meta-analysis that combined the results of 11 prospective cohort studies found that people in the 90th percentile of fruit and vegetable intake (about 5 servings/day or more; for information about serving size, please see Examples of One Serving of Fruits or Vegetables below) had a risk of myocardial infarction (MI) that was approximately 15% lower than those in the 10th percentile of intake (3). Among more than 126,000 men and women participating in the Health Professionals' Follow-up Study and the Nurses’ Health Study, those who consumed eight or more servings of fruits and vegetables daily had a risk of developing CHD over the next 8-14 years that was 20% lower than those who consumed less than three servings daily (4). In the same cohort, the risk of ischemic stroke (stroke caused by a reduction in blood flow to part of the brain) was 30% lower in those who consumed at least five servings of fruits and vegetables daily than in those who consumed less than three servings daily (5). Based on the results of Health Professionals' Follow-up Study and the Nurses’ Health Study, eating one extra serving of fruits or vegetables daily would decrease one’s risk of CHD by about 4% and decrease risk of ischemic stroke by 6%. In a meta-analysis designed to estimate the global burden of disease attributable to low fruit and vegetable consumption, epidemiologists concluded that increasing individual fruit and vegetable consumption (excluding potatoes) up to 600 g/day (about 7 servings/day) could decrease the risk of CHD by 31% and the risk of ischemic stroke by 19% (1). Three recent meta-analyses have examined fruit and vegetable consumption and risk of CHD or stroke. In a meta-analysis that included nine cohort studies, an additional daily serving of fruit and vegetables was associated with a 4% decreased risk for CHD (6). Another meta-analysis, which examined 12 separate studies, found that individuals who consumed more than five daily servings of fruit and vegetables experienced a 17% reduction in risk of CHD compared to those who consumed less than three servings daily (7). In a meta-analysis of eight studies examining fruit and vegetable intake, individuals who consumed three to five daily servings or more than five daily servings had an 11% or 26% reduction in risk of stroke, respectively, when compared to those who consumed less than three servings daily (8).
High blood pressure (hypertension) increases the risk of heart disease and stroke (9). Adding more fruits and vegetables to a sensible diet is one potential way to lower blood pressure. In the Dietary Approaches to Stop Hypertension (DASH) study, 459 people with and without high blood pressure were randomly assigned to one of three diets: 1) a typical American diet that provided about 3 servings/day of fruits and vegetables and 1 serving/day of a low-fat dairy product, 2) a fruit and vegetable diet that provided 8 servings/day of fruits and vegetables and 1 serving/day of a low-fat dairy product, or 3) a combination diet (now called the DASH diet) that provided 9 servings/day of fruits and vegetables and 3 servings/day of low-fat dairy products (10). After eight weeks, the blood pressures of those on the fruit and vegetable diet (8 servings/day) were significantly lower than those on the typical American diet, while blood pressures of those on the combination (DASH) diet (9 servings/day of fruits and vegetables) were lower still. For more information on the DASH eating plan, go to the National Heart, Lung, and Blood Institute Web site.
A number of compounds may contribute to the cardioprotective effects of fruits and vegetables, including vitamin C, folate, potassium, fiber, and various phytochemicals (11). However, supplementation of individual micronutrients or phytochemicals has not generally resulted in significantly decreased incidence of cardiovascular events in randomized controlled trials. Thus, in the case of fruits and vegetables, the benefit of the whole may be greater than the sum of its parts.
In addition to other complications, type 2 diabetes mellitus (DM) is associated with increased risk of cardiovascular disease—the leading cause of death in type 2 diabetics (12). Although the evidence for a beneficial effect of a diet rich in fruits and vegetables on diabetes is not as consistent as it is for heart disease, the results of a small number of studies suggest that higher intakes of fruits and vegetables are associated with improved blood glucose control and lower risk of developing type 2 DM. In a cohort of almost 10,000 adults in the United States, the risk of developing type 2 DM over the next 20 years was approximately 20% lower in those who reported consuming at least five daily servings of fruits and vegetables compared to those who reported consuming none (13). In another prospective cohort study that followed more than 40,000 U.S. women for an average of nine years, fruit and vegetable intake was not associated with the risk of developing type 2 DM in the entire cohort, but higher intakes of green leafy and yellow vegetables were associated with significant reductions in the risk of type 2 DM in overweight women (14). Higher fruit and vegetable intakes were weakly associated with a reduced risk of diabetes in a cohort of more than 20,000 individuals followed for 12 years (15). In a cohort of 71,346 women participating in the Nurses' Health Study, total fruit and vegetable intake was not associated with risk for diabetes, although further analysis revealed that intake of fruit or green leafy vegetables was individually associated with a modest reduction in risk of diabetes (16). A systematic review and meta-analysis of five cohort studies found that fruit and vegetable intake was not associated with type 2 diabetes (17). However, in a cross-sectional study of more than 6,000 nondiabetic adults in the UK, those with higher fruit and vegetable intakes had significantly lower levels of glycosylated hemoglobin (HbA1c), a measure of long-term blood glucose control (18). Possible compounds in fruits and vegetables that may enhance glucose control include fiber and magnesium.
The results of numerous case-control studies indicate that eating a diet rich in fruits and vegetables decreases the risk of developing a number of different types of cancer, particularly cancers of the digestive tract (oropharynx, esophagus, stomach, colon, and rectum) and lung (19-21). The results of some of these studies were the foundation for the National Cancer Institute’s “5 a Day” program, which was aimed at increasing the fruit and vegetable consumption of the American public to a minimum of five servings daily. The current U.S. government campaign, Fruits & Veggies-More Matters™, has replaced the "5 a Day" program. In contrast to the results of case-control studies, many recent prospective cohort studies have found little or no association between total fruit and vegetable intake and the risk of various cancers (22-44). There are several possible explanations for this discrepancy. Case-control studies, in which the past diets of people diagnosed with a particular type of cancer are compared to the diets of people without cancer, are more susceptible to bias in the selection of participants and dietary recall than prospective cohort studies, which collect information on the diets of large cohorts of healthy people and follow the development of disease in the cohort over time (45). Although prospective cohort studies provide weak support for an association between total fruit and vegetable consumption and cancer risk, they provide some evidence that high intakes of certain classes of fruits or vegetables are associated with reduced risk of individual cancers. Higher intakes of fruits have been associated with modest but significant reductions in lung cancer risk in a pooled analysis of eight prospective cohort studies (28) and with reductions in risk of bladder cancer in some studies (46). In men, higher intakes of cruciferous vegetables have been associated with significant reductions in the risk of bladder cancer (47) as well as prostate cancer (48), and higher intakes of tomato products have been linked with significant reductions in risk of prostate cancer (49).
Several cross-sectional studies have reported that higher intakes of fruits and vegetables are associated with significantly higher bone mineral density (BMD) and lower levels of bone resorption (loss) in men and women (50-53). In a study that followed BMD over four years, higher fruit and vegetable intakes were associated with significantly less decline in BMD at the hip in elderly men but not elderly women (50). Fruits and vegetables are rich in precursors to bicarbonate ions, which serve to buffer acids in the body. When the quantity of bicarbonate ions is insufficient to maintain normal pH, the body is capable of mobilizing alkaline calcium salts from bone in order to neutralize acids consumed in the diet and generated by metabolism (54). Increased consumption of fruits and vegetables reduces the net acid content of the diet and may preserve calcium in bones, which might otherwise be mobilized to maintain normal pH. However, the results of a recent placebo-controlled trial in 276 postmenopausal women suggest that supplementing the diet with alkali, either through supplemental potassium citrate or an additional 300 g/day of fruits and vegetables, did not increase BMD or blunt the age-associated bone loss over a two-year period (55). Results from the DASH study support a beneficial link between fruit and vegetable intake and bone health. In addition to decreasing blood pressure, increasing fruit and vegetable intakes from about 3 to 9 servings daily decreased urinary calcium loss by almost 50 mg/day (10) and lowered biochemical markers of bone turnover, particularly bone resorption, including serum levels of C-terminal telopeptide of type 1 collagen (56). Taken together, the results of epidemiological studies and controlled clinical trials suggest that a diet rich in fruits and vegetables can help prevent bone loss, although the specific mechanisms are not known with certainty.
Cataracts are thought to be caused by oxidative damage of proteins in the eye’s lens induced by long-term exposure to UV light. The resulting cloudiness and discoloration of the lens leads to vision loss that becomes more severe with age. The results of several large prospective cohort studies suggest that diets rich in fruits and vegetables, especially carotenoid and vitamin C-rich fruits and vegetables, are associated with decreased incidence and severity of cataracts (57-60). In a study of male U.S. health professionals, high intakes of both broccoli and spinach were associated with fewer cataract extractions (57).
Degeneration of the macula, the center of the retina, is the leading cause of blindness in people over the age of 65 in the United States (61). Lutein and zeaxanthin are carotenoids that are found in relatively high concentrations in the retina; these carotenoids may play a role in preventing damage to the retina caused by light or oxidants (62). In two case-control studies, high intakes of carotenoid-rich vegetables, especially those rich in lutein and zeaxanthin, such as dark green, leafy vegetables, were associated with a significantly lower risk of developing age-related macular degeneration (AMD) (63, 64). In a prospective cohort study of more than 118,000 men and women, those who consumed three or more servings of fruits daily had a risk of developing age-related macular degeneration over the next 12-18 years that was 36% lower than those who consumed less than 1.5 servings (65). Interestingly, vegetable intake was not associated with the risk of macular degeneration in this cohort. In a more recent study, combined lutein and zeaxanthin intake was not associated with prevalence of intermediate AMD in a cohort of women aged 50-79 years (66). However, further analysis of the data revealed that women younger than 75 years with stable intakes of lutein and zeaxanthin had a 43% lower risk of developing intermediate AMD (66).
Chronic obstructive pulmonary disease (COPD) is a term that includes emphysema and chronic bronchitis, two chronic lung diseases that are characterized by airway obstruction. Although smoking is by far the most important risk factor for COPD, the results of several epidemiological studies suggest beneficial associations between vegetable and, more strongly, with fruit intakes and COPD risk (67). The results of several epidemiological studies in Europe indicate that higher fruit intakes, especially apple intakes, are associated with higher forced expiratory volume (FEV1) values, indicative of better lung function (68-70). In a study of 2,500 middle-aged Welsh men, those who ate at least five apples weekly had significantly slower declines in lung function than those who did not eat apples over a 5-year period (69). In a study of 2,917 European men followed over 20 years, each 100 g (3.5 oz) increase in daily fruit consumption was associated with a 24% decrease in the risk of death from COPD (71). The reasons for the beneficial association between fruit intake and lung health are not yet known. Because oxidative stress is thought to play a role in the etiology of chronic obstructive lung disease, scientists are currently investigating the possibility that antioxidants found in fruits, such as vitamin C or flavonoids, could play a protective role. Higher fruit and vegetable intake was inversely associated with risk of COPD in a small case-control study of male cigarette smokers (72), providing support for the antioxidant hypothesis. Interestingly, when compared to a Western dietary pattern (refined grains, cured and red meats, French fries, and desserts), a prudent dietary pattern that emphasized fruits, vegetables, fish, and whole grains was associated with a 25-50% reduction in COPD risk in large cohorts of men (73) and women (74).
Although it is not yet clear whether a diet rich in fruits and vegetables will decrease the risk of neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease in humans, recent studies in animal models of these diseases suggest that diets rich in fruits like blueberries (75) or tomatoes may be protective (76). Interestingly, a prospective study that followed 1,836 older Japanese Americans for an average of 6.3 years found that regular consumption of fruit and vegetable juices was associated with a decreased risk of developing Alzheimer's disease (77). More studies are needed to determine whether fruit and vegetable consumption is protective against neurodegenerative diseases.
Many agencies within the U.S. government, including the Centers for Disease Control and Prevention, recommend eating a variety of fruits and vegetables daily; the recommended serving number depends on age, sex, and activity level (78). The table below provides some examples of a single serving of fruits or vegetables. The 2005 Dietary Guidelines for Americans are similar with respect to fruit and vegetable intake recommendations, but they are tied to caloric intake and not to age or gender (79). Daily consumption of 2 cups (4 servings) of fruit and 2½ cups (5 servings) of vegetables are recommended for people who consume 2,000 kcal/d, while 1.5 cups of fruit and (3 servings) and 2 cups (4 servings) of vegetables are recommended for people who consume 1,600 kcal/d. In both cases, consumption of a variety of different fruits and vegetables is recommended, including dark green, red, orange, yellow, blue, and purple fruits and vegetables, as well as legumes (peas and beans), onions, and garlic. The Linus Pauling Institute's Prescription for Health states that potatoes should not be included in the daily tally of fruit and vegetable intake. Moreover, certain groups of fruits and vegetables, such as cruciferous vegetables, may provide specific health benefits (see the article on Cruciferous Vegetables). Additionally, fiber-rich, whole fruits are recommended over high-sugar fruit juices.
|Some Potentially Beneficial Compounds in Fruits and Vegetables|
Written in December 2005 by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in May 2009 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University
Reviewed in May 2009 by:
Kaumudi Joshipura, Sc.D.
Professor of Epidemiology
Harvard School of Public Health
Harvard School of Dental Medicine
Last updated 4/7/2010 Copyright 2003-2013 Linus Pauling Institute
The Linus Pauling Institute Micronutrient Information Center provides scientific information on the health aspects of dietary factors and supplements, foods, and beverages for the general public. The information is made available with the understanding that the author and publisher are not providing medical, psychological, or nutritional counseling services on this site. The information should not be used in place of a consultation with a competent health care or nutrition professional.
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