Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
by Reed Mangels, PhD, RD, FADA
Vegetarians and Colon Cancer
Colon cancer is the third most lethal cancer in the United States, after lung and breast cancer. Diet has been identified as the most important risk factor for developing colon cancer. Are vegetarians at lower risk for developing colon cancer? A study of Seventh-day Adventists found that colon cancer occurred more commonly in non-vegetarians than in vegetarians (Am J Epidemiol 1998; 148:761-74). A more recent study of vegetarians and non-vegetarians in the United Kingdom found that vegetarians did have a moderately lower risk of colon cancer but that this was not statistically significant. The authors speculate that the non-vegetarians in their study were healthier than the general population, so their rates of colon cancer could be lower than is typical. This study did find associations between higher fruit intake and lower risk of colon cancer. Colon cancer risk was increased by smoking and alcohol use.
Sanjoaquin MA, Appleby PN, Thorogood M, et al. 2004. Nutrition, lifestyle and colorectal cancer incidence: a prospective investigation of 10998 vegetarians and non-vegetarians in the United Kingdom. Br J Cancer 90:118-21.
Why Eat Fruits and Vegetables?
Most of us have heard of colon cancer, sometimes called colorectal cancer. Rectal cancer may be a less familiar term. The rectum, where rectal cancer occurs, is located at the end of the large intestine; it is about 7 inches long. About 1 of 8 deaths from colorectal cancer is due to rectal cancer. Some, but not all, studies of colon cancer have found that high fiber diets reduce risk. Do high fiber diets reduce risk of rectal cancer? Researchers from the University of Utah examined 952 people with rectal cancer and compared them to 1,205 people without rectal cancer. Subjects were asked to recall their diet two years before the start of the study, which, for the people with cancer, was two years before their cancer was diagnosed. Fruit, vegetables, and whole-grains were associated with a reduced risk of developing rectal cancer. High intakes of dietary fiber also reduced the risk of cancer. While some may question whether a person’s diet two years before they are diagnosed with cancer reflects their lifetime diet, these results are consistent with other studies of colorectal cancer that show that diets high in vegetables and fruits can help to protect against this disease.
Slattery ML, Curtin KP, Edwards SL, Schaffer DM. 2004. Plant foods, fiber, and rectal cancer. Am J Clin Nutr 79:274-81.
Another Reason to Eat Fruits and Vegetables — Bone Loss
Women tend to have a significant and rapid loss of bone mass around menopause. Most research in this area has centered on the roles of calcium and vitamin D in reducing bone loss. A new study suggests that fruit and vegetable intake may protect somewhat against bone loss. The study examined 891 women aged 45-55 years at the start of the study and 50-59 years at follow-up. The women’s bone density was measured at both study periods, and they were asked about their diets. As you might expect, a higher calcium intake was associated with less bone loss. Women whose diets were low in calcium experienced a greater bone loss if their diets were also high in polyunsaturated and monounsaturated fats. This may be because of the overall pattern of the women’s diets or because fat intake influenced bone health. For women who had not yet started menopause, calcium and nutrients found in fruits and vegetables (vitamin C, magnesium, and potassium) were associated with protection against bone loss. The bottom line: adequate calcium, fruits, and vegetables are important for bone health in the years around menopause.
Macdonald HM, New SA, Golden MHN, et al. 2004. Nutritional associations with bone loss during the menopausal transition: evidence of a beneficial effect of calcium, alcohol, and fruit and vegetable nutrients and of a detrimental effect of fatty acids. Am J Clin Nutr 79:155-65.
And Yet Another Reason — Lower LDL-Cholesterol
LDL-cholesterol is also called “bad” cholesterol because high levels of LDL-cholesterol in the blood are associated with increased risk of heart disease. The usual dietary recommendations for reducing LDL-cholesterol call for reducing dietary saturated fat and cholesterol. There’s something else those with high LDL-cholesterol levels can do—namely, they can eat more fruits and vegetables. A study of more than 4,000 men and women in the United States found that those who ate the greatest number of servings of fruits and vegetables had the lowest levels of LDL-cholesterol. This held true even when other risk factors like age, smoking, and physical activity were controlled for. Certainly it is helpful to limit or avoid dietary saturated fat and cholesterol, but don’t forget to eat plenty of fruits and vegetables as well!
Djousse L, Arnett DK, Coon H, et al. 2004. Fruit and vegetable consumption and LDL cholesterol: the National Heart, Lung, and Blood Institute Family Heart Study. Am J Clin Nutr 79:213-17.
Fruits and Vegetables Are Good for Pre-Teens’ Bones
There is increasing evidence that fruits and vegetables are good for adults’ bones. A new study suggests that they are also important for pre-teen girls. Researchers at the University of Tennessee studied 56 girls between the ages of 8 and 13 years. The girls were asked how many servings of fruits and vegetables they ate in a day. They were divided into two groups - girls eating three or more servings of fruits and vegetables daily and girls eating fewer than three servings per day. There was no difference in consumption of cow’s milk or meat between the groups, nor were the groups different in total calcium, phosphorus, vitamin D, or protein intake. The group eating more fruits and vegetables had a higher bone mass and lower urinary calcium losses. Higher bone mass appears to reduce risk of osteoporosis later in life. Vegetarian girls often eat more than three servings of fruits and vegetables daily. It would be interesting to see if even higher intakes than those reported in this study would have an even larger impact on bone health.
Tylavsky FA, Holliday K, Danish R, et al. 2004. Fruit and vegetable intakes are an independent predictor of bone size in early pubertal children. Am J Clin Nutr 79:311-17.
Experts Recommend Dietary Changes to Prevent Cancer
Experts in nutrition from the United States and the United Kingdom recently looked at many studies on diet and cancer and made specific recommendations for cancer prevention. Key recommendations include avoiding overweight and obesity, which increase risk of cancer of the esophagus, kidney, colon, and breast; eating at least 13 ounces of fruits and vegetables daily to reduce risk of cancer of the esophagus, stomach, colon, and mouth; limiting or avoiding red meat and preserved meat to reduce risk of colon cancer; moderating salt intake to reduce risk of stomach cancer; and avoiding very hot or scalding drinks and foods to reduce risk of cancer of the mouth and esophagus. Physical activity appears to reduce risk for colon cancer and breast cancer. After tobacco, overweight and obesity appear to be the most important avoidable causes of cancer.
Key TJ, Schatzkin A, Willett WC, et al. 2004. Diet, nutrition, and the prevention of cancer. Public Health Nutr 7:187-200.
Why Are Americans Getting Fatter?
Between 1971 and 2000, the prevalence of obesity in the United States increased from 14.5 percent to 30.9 percent. Why? A recent report suggests that a large part of the problem is that people in the United States are eating more calories. In 1971, the average man ate 2,450 calories per day; in 2000, he ate 2,618 calories. The average woman ate 1,542 calories in 1971 and 1,877 calories in 2000. While this report did not look at exercise habits, the general consensus is that we are exercising less. The combination of these factors—higher caloric intake and less exercise—has led to an epidemic of obesity. Factors contributing to this rise in caloric intake include increased portion sizes, increased use of salty snacks and soft drinks, and increased consumption of food away from home.
Trends in intake of energy and macronutrients—United States, 1971-2011. 2004. MMWR 53:80-82.
