Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

By Reed Mangels, PhD, RD, FADA

Hold the Beef and the Bacon

Colorectal cancer is the third most common cancer in the United States and the second most common cause of cancer deaths. The American Cancer Society estimates that colorectal cancer caused more than 56,000 deaths in 2005. Obesity, physical inactivity, and high alcohol consumption are some of the factors associated with an increased risk of colorectal cancer. An estimated 70 percent of colorectal cancers in Western countries could be avoided by lifestyle changes. Some studies have shown that one of these changes could be switching to a vegetarian diet; vegetarians have been shown to have a lower risk of colon cancer than non-vegetarians. A recent study of more than 478,000 men and women from 10 European countries examined the effect of meat, poultry, and fish intake on colorectal cancer risk. In this group of mainly non-vegetarians, higher fish intake was associated with a lower risk of colorectal cancer; poultry consumption did not appear to affect cancer risk. People with high intakes (more than 5 ounces per day) of red meat (beef, veal, pork, and lamb) and processed meat (ham, bacon, sausage, lunch meat, etc.) had a higher risk of developing colorectal cancer than did people averaging less than an ounce of red and processed meat daily. Veggie burgers, anyone?

Norat T, Bingham S, Ferrari P, et al. 2005.
Meat, fish, and colorectal cancer risk: the European Prospective Investigation into Cancer and Nutrition. J Natl Cancer Inst 97:906-16.

DHA Supplementation of Breastfeeding Women

Docosahexaenoic acid (DHA) is a fatty acid that is found in fish. Humans make some DHA from linolenic acid, a fatty acid found mainly in flaxseed and flaxseed oil and in lesser amounts in soybeans, canola oil, and walnuts. DHA appears to play a role in brain development and in vision in infants and is added to some infant formulas. The DHA level of breastmilk reflects the mother’s DHA intake, with vegetarian women having lower milk DHA levels than non-vegetarian women. A vegan DHA supplement derived from microalgae has been developed. (See Vegetarian Journal, Issue 3, 2005.) USDA researchers examined whether use of a DHA supplement by breastfeeding women would affect their infants’ development. Study subjects were divided into two groups. One group received capsules containing DHA derived from microalgae; the other group’s capsules contained soy and corn oils. Subjects took their capsules daily for four months after their babies’ births. As expected, levels of DHA in breastmilk were higher in the group taking DHA supplements, and infants of women taking DHA supplements had higher levels of DHA in their blood. DHA supplementation of breastfeeding women did not affect their infants’ vision. Infants whose mothers took DHA supplements did score higher on one developmental test at 30 months of age but did not have higher scores on other tests or at other ages. These results suggest that increased DHA may be of some benefit to breastfed infants, although the benefit may be small.

Jensen CL, Voigt RG, Prager TC, et al. 2005.
Effects of maternal docosahexaenoic acid on visual function and neurodevelopment in breastfed term infants. Am J Clin Nutr 82:125-32.

Oh Say, Can You See?

Cataract (clouding of the lens of the eye) is the number one cause of blindness worldwide. Currently, nearly one in five Americans age 40 or older has cataracts. Medicare spends more than $3.4 billion per year for treatment of this condition. If dietary changes could reduce the risk of developing cataracts, the impact on health care costs would be staggering. Very few studies have examined dietary risk factors for cataract.

Recently, two studies were published, one which examined fruit and vegetable consumption and cataract risk and another which examined carbohydrate consumption and cataract risk. Both studies were of middle-aged and older women. Women who ate more than 3.4 servings of fruits and vegetables daily had a slightly lower (10-15 percent) risk of developing cataracts and having surgery to remove them. While these results are modest, increased fruit and vegetable intake can’t hurt, may reduce risk of cataracts, and certainly helps to reduce the risk of many other diseases.

The second study found that higher carbohydrate intakes were associated with an increased risk of one type of cataract called cortical cataracts. Since this type of cataract represents only a small proportion of cataracts that are surgically removed, the practical implications of these results are uncertain. At this point, increasing fruit and vegetable intake appears to be one way to reduce the risk of developing cataracts.

Christen WG, Liu S, Schaumberg DA, Buring JE. 2005.
Fruit and vegetable intake and the risk of cataract in women. Am J Clin Nutr 81:1417-22.
Chiu C-J, Morris MS, Rogers G, et al. 2005.
Carbohydrate intake and glycemic index in relation to the odds of early cortical and nuclear lens opacities. Am J Clin Nutr 81:1411-16.

Mortality Among German Vegetarians Versus ‘Health- Conscious’ Non-Vegetarians

In 1976, 1,225 vegetarians and 679 ‘health-conscious’ non-vegetarians in Germany were recruited for a long-term study. The group being studied included vegans (3 percent), lacto-ovo vegetarians (61 percent), and non-vegetarians (36 percent). Twenty-one years later, researchers determined which of the subjects had died and what had caused their deaths. Overall, this group had a much lower rate of death than the general population, mainly because of many fewer deaths from heart disease. Vegetarians had lower rates of death from heart disease than non-vegetarians, even in this study where non-vegetarians were health-conscious. Death rates from cancer were similar in both groups. Individuals who were moderately or highly physically active were less likely to die from cancer or heart disease than those who were more sedentary. There was a trend of increased risk of dying from heart disease as meat consumption increased. Eating fish more than once a month was also associated with an increased risk of death from heart disease. Many results of this study are in accord with studies of British vegetarians and of Seventh-day Adventist vegetarians in the United States.

Chang-Claude J, Hermann S, Eilber U, Steindorf K. 2005.
Lifestyle determinants and mortality in German vegetarians and health-conscious persons: results of a 21-year follow-up. Epidemiol Biomarkers Prev 14:963-68.

Self-Defined Vegetarians in British Columbia, Canada, Show Healthier Dietary and Lifestyle Practices

Recently, a study of men and women living in British Columbia, Canada, showed that vegetarians were more physically active than non-vegetarians and were more likely to consider improving or maintaining their health when choosing foods. This was a population-based study using the British Columbia Health Registry, so the participants mirror the general British Columbian population. This study is also significant because few population-based studies have compared dietary intake and behavior between vegetarians and non-vegetarians.

Of the 1,817 participants, approximately 6 percent identified themselves as vegetarian. However, of this 6 percent, 75 percent consumed fish at least occasionally, 58 percent consumed poultry at least occasionally, and 22 percent consumed red meat at least occasionally. Vegetarians in this population tended to be mainly lacto-ovo vegetarians, and they tended to be younger, female, and low-income in status. Female vegetarians tended to engage in moderate to strenuous physical activity most days of the week and were less likely to be classified as overweight or obese compared to female non-vegetarians. Both male and female vegetarians were less likely to be smokers.

Both male and female vegetarians had more fiber, magnesium, and potassium in their diets and used more supplements than non-vegetarians. This study also found female vegetarians were less likely to have inadequate intakes of folate, vitamin B6, thiamin, and vitamin C compared to non-vegetarians. Vegetarians of both genders consumed more fruits and vegetables and were more likely to consider health when choosing or avoiding food compared to non-vegetarians. Taken altogether, vegetarians were, as readers might expect, more health conscious as evidenced by their increased awareness and practice of dietary and lifestyle considerations that are important in maintaining good health.

Bedford JL, Barr SI. 2005.
Diets and selected lifestyle practices of self-defined adult vegetarians from a population-based sample suggest they are more ‘health conscious.’ Int J Behav Nutr Phys Act 2:4.

This review of a study examining the dietary habits and lifestyle choices of British Columbian vegetarians was written by Melissa Wong, VRG Dietetic Intern.