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 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). 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/d or more) 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 8 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 3 servings daily (4). In the same men and women, 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 5 servings of fruits and vegetables daily than in those who consumed less than 3 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 the 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 to 600 g/d (about 7 servings/d) could decrease the risk of CHD by 31% and the risk of ischemic stroke by 19% (1).
High blood pressure (hypertension) increases the risk of heart disease and stroke (6). 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/d of fruits and vegetables and one serving/d of a low-fat dairy product, 2) a fruit and vegetable diet that provided 8 servings/d of fruits and vegetables and one serving/d of a low-fat dairy product, or 3) a combination diet (now called the DASH diet) that provided 9 servings/d of fruits and vegetables and 3 servings/d of low-fat dairy products (7). After 8 weeks, the blood pressures of those on the fruit and vegetable diet were significantly lower than those on the typical American diet, while blood pressures of those on the combination (DASH) diet 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 other phytochemicals (8). 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 its other complications, type 2 diabetes mellitus (DM) is associated with increased risk of cardiovascular disease, the leading cause of death in type 2 diabetics (9). 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 US, the risk of developing type 2 DM over the next 20 years was approximately 20% lower in those who reported consuming at least 5 servings/d of fruits and vegetables compared to those who reported consuming none (10). In another prospective cohort study that followed more than 40,000 US women for an average of 9 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 (11). 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 (12). 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 (13, 14). The results of these studies are the foundation for the National Cancer Institute’s “5 a Day” program, which is aimed at increasing the fruit and vegetable consumption of the American public to a minimum of five servings daily. 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 (15-26). 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 (27). 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 were associated with modest but significant reductions in lung cancer risk in a pooled analysis of 8 prospective cohort studies (21). In men, higher intakes of cruciferous vegetables were associated with significant reductions in the risk of bladder cancer (28) and higher intakes of tomato products were associated with significant reductions in the risk of prostate cancer (29).
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 (30-32). In a study that followed BMD over 4 years, higher fruit and vegetable intakes were associated with significantly less decline in BMD at the hip in elderly men but not elderly women (30). 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 (33). 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. Results from the DASH study also 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 servings to 9 servings daily decreased urinary calcium loss by almost 50 mg/day (7) and lowered biochemical markers of bone turnover, particularly bone resorption (34). Taken together, the results of epidemiological and controlled clinical trials suggest that a diet rich in fruits and vegetables can help prevent bone loss.
Cataracts
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 becomes 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 (35-38). In a study of male U.S. health professionals, high intakes of both broccoli and spinach were associated with fewer cataract extractions (35).
Degeneration of the macula, the center of the retina, is the leading cause of blindness in people over the age of 65 in the U.S (39). Lutein and zeaxanthin are carotenoids that are found in relatively high concentrations in the retina, and may play a role in preventing damage to the retina caused by light or oxidants (40). In two case-control studies, high intakes of carotenoid-rich vegetables, especially those rich in lutein and zeaxanthin, were associated with a significantly lower risk of developing age-related macular degeneration (41, 42). More recently a prospective cohort study of more than 118,000 men and women found that those who consumed 3 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 (43). Interestingly, vegetable intake was not associated with the risk of macular degeneration in this cohort.
Chronic Obstructive Pulmonary Disease
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, particularly, fruit intakes and COPD risk (44). 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 (45-47). In a study of 2500 middle-aged Welsh men, those who ate at least 5 apples weekly had significantly slower declines in lung function than those who did not eat apples over a 5-year period (46). In a study of 2917 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 (48). 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.
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 high in fruits like blueberries (49) or tomatoes may be protective (50).
The National Cancer Institute recommends a range of 5-9 servings of fruits and vegetables daily (51). Specifically, adolescent and adult women should aim for 7 daily servings while adolescent and adult men should aim for 9 daily servings. 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 rather than age and gender (52). Daily consumption of 2 cups (4 servings) of fruit and 2½ cups (5 servings) of vegetables are recommended for people who consume 2000 kcal/d, while 1.5 cups of fruit and (3 servings) and 2 cups (4 servings) of vegetables are recommended for people who consume 1600 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.
Examples of One Serving of Fruits or Vegetables
| Some Potentially Beneficial Compounds in Fruits and Vegetables | ||
Vitamins |
Minerals |
Phytochemicals |
| Folate | Magnesium | Carotenoids |
| Vitamin C | Potassium | Chlorophylls |
| Vitamin E | Selenium | Fiber |
| Vitamin K | Flavonoids | |
| Indole-3-Carbinol | ||
| Isoflavones | ||
| Isothiocyanates | ||
| Lignans | ||
| Phytosterols | ||
Written by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Reviewed by:
Kaumudi Joshipura, Sc.D.
Associate Professor of Epidemiology
Harvard School of Public Health
Associate Professor
Harvard School of Dental Medicine
Last updated 12/16/05 Copyright 2003-2008 Linus Pauling Institute
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The Linus Pauling Institute Micronutrient Information Center provides scientific information on health aspects of micronutrients and phytochemicals 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.
The information on micronutrients and phytochemicals contained on this Web site does not cover all possible uses, actions, precautions, side effects, and interactions. It is not intended as medical advice for individual problems. Liability for individual actions or omissions based upon the contents of this site is expressly disclaimed.