Eating More Fruits and Vegetables May Lower Risk of Heart Disease, Not Cancer
Eating plenty of fruits and vegetables has long been associated with good health. As such, eating five or more servings of these colorful plant foods has been recommended to reduce a person's risk of chronic disease, including cardiovascular disease and cancer. Yet surprisingly, there has been little data to support this recommendation. Alas, research is catching up to folklore.
A new Harvard study reports that eating more than eight servings of fruits and vegetables a day is associated with a modest reduction in the development of major chronic diseases, which includes both cancer and ]]>heart disease]]> . However, the researchers also analyzed cancer and heart disease separately and found that higher fruit and vegetable intake was not associated with lower risk of cancer, but was associated with lower risk of heart disease.
This study, published in the November 3, 2004 issue of the Journal of the National Cancer Institute , appears to contradict current “five-a-day” fruit and vegetable intake recommendations for cancer prevention. However, the design of the study may not have allowed the full benefits of fruits and vegetables to be detected.
About the Study
Researchers at Harvard University recorded fruit and vegetable consumption of 71,910 women in the Nurses’ Health Study and 37,725 men in the Health Professionals’ Follow-up Study. The participants were given a food-frequency questionnaire containing several questions on fruit and vegetable intake and asked to report how frequently they consumed each food in a given year. The men and women were followed for 14 and 12 years, respectively, and they provided updated dietary information every 2–4 years .
The researchers followed the participants to determine whether they developed cardiovascular disease or cancer, or died during the course of the study. Researchers grouped participants into five groups according to their fruit and vegetable intake, ranging from one-and-a-half servings to eight servings. They then statistically analyzed whether fruit and vegetable intake was associated with chronic disease, which included both cardiovascular disease and cancer.
Participants who consumed more than eight servings of fruits and vegetables per day had a slightly lower risk of major chronic disease than those who consumed less than one-and-a-half servings. This finding, however, was not statistically significant.
But when the two chronic diseases were analyzed separately, the results changed substantially. Increased fruit and vegetable consumption was not associated with lower risk of cancer, but was associated with moderately lower risk of heart disease.
The researchers also separately analyzed different types of vegetables, such as green leafy vegetables and cruciferous vegetables, to determine if any relationships with chronic disease existed. Only green leafy vegetables were associated with a lower risk of chronic disease in those people consuming the most fruits and vegetables compared to those people consuming the least.
The researchers tried to consider factors besides fruit and vegetable intake that may also contribute to cancer or heart disease, such as calories consumed, age, exercise, family history, and smoking status, and adjusted their analyses to account for these factors. However, it is difficult to completely eliminate the possibility that factors other than fruit and vegetable consumption influenced the results.
Further, another major limitation of this study is in the assessment of fruit and vegetable intake. Population studies like this one rely on the use of nutrition assessment tools, such as the food frequency form, to estimate fruit and vegetable consumption. These tools may fail to accurately estimate fruit and vegetable intake, which makes the outcome of the study less conclusive.
Finally, it is possible that because fruits and vegetables of different colors and textures provide a wealth of different nutrients, analyzing them as a whole may mask their individual affects on the prevention of specific chronic diseases.
How Does This Affect You?
The authors conclude that their results “support the recommendation of consuming five or more fruits and vegetables daily.” Their findings suggest that increased fruit and vegetable intake indeed appears to be beneficial for the prevention of chronic disease, particularly heart disease. However, more research is needed to determine if fruit and vegetable consumption is also associated with lower risk of cancer.
Nonetheless, there are many reasons to consume fruits and vegetables and virtually no reasons not to. Fruits and vegetables are:
- Low in calories, which helps facilitate weight loss
- Full of vitamins and minerals needed for normal growth and development
- Rich in fiber, which plays a part in bowel regularity, body weight, blood sugar control, and cholesterol
- Packed with phytochemicals, or special substances in plant foods that researchers are only beginning to discover may help prevent chronic diseases, such as lycopene in tomatoes and resveratrol in red wine and peanuts
Therefore, eating a variety of colorful fruits and vegetables would not only be delicious, but wise.
National Cancer Institute 5 A Day Program
Hung H, Joshipura KJ, Jiang R, et al. Fruit and vegetable intake and risk of major chronic disease. Journal of the National Cancer Institute. 2004;96(21):1577–1584.
Schatzkin A, Kipnis V. Could exposure assessment problems give us wrong answers to nutrition and cancer questions? Journal of the National Cancer Institute. 2004;96(21):1564–1565.
Last reviewed Nov 4, 2004 by ]]>Richard Glickman-Simon, MD]]>
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