VRG > Vegetarian Journal > 2005 Issue 2 > Scientific Update

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Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

By Reed Mangels, PhD, RD, FADA

Diet High in Vegetable Protein Reduces Risk of Gall Bladder Surgery

This year, more than 500,000 Americans will have gallstones that lead to surgery to remove their gall bladders. Cholecystectomy, the surgical removal of the gall bladder, is the most commonly performed surgical procedure in the United States. Costs associated with gall bladder disease account for more than $6.5 billion annually. Dietary choices can reduce the risk of surgery to remove the gall bladder. A large study of more than 80,000 women found that women with a high intake of vegetable protein had a lower risk of having their gall bladders removed than did women eating very little vegetable protein. These results suggest that the use of a diet with protein mainly (or solely) derived from plants could reduce the number of cholecystectomies and reduce health care costs.

Tsai C-J, Leitzmann MF, Willett WC, Giovannucci EL. 2004.

Dietary protein and the risk of cholecystectomy in a cohort of US women. Am J Epidemiol 160:11-18.

Red Meat Associated with Type 2 Diabetes in Women

Type 2 diabetes (formerly called adult-onset diabetes) has reached epidemic proportions in this country. More than 16 million Americans have this disease. A recent study examined dietary factors that were associated with type 2 diabetes. More than 35,000 women were studied for almost nine years to see which ones would develop type 2 diabetes. As intake of red meat, processed meat, or both items increased, so did the women’s risk of type 2 diabetes. Higher intakes of cholesterol, animal protein, and heme iron (from meat) were also associated with increased risk. These results suggest that women, especially those who already are at increased risk for type 2 diabetes (family history, overweight), should markedly limit their consumption of red meat. It also suggests, as do other studies, that vegetarians have a lower risk for type 2 diabetes than do non-vegetarians.

Song Y, Manson JE, Buring JE, Liu S. 2004.

A prospective study of red meat consumption and type 2 diabetes in middle-aged and elderly women: the women’s health study. Diabetes Care 27:2108-15.

Moderate Use of Soyfoods Reduces Blood Cholesterol Levels in Women

A number of studies have found that adding generous amounts of soy protein to people’s diets leads to a reduction in blood cholesterol levels. Is it possible to see an effect with intakes of soy that are closer to what people typically eat? A study from the University of Oxford examined vegetarians, vegans, and non-vegetarians to address this question. More than 1,000 postmenopausal women, including 570 vegetarians and 102 vegans, were studied. Women were asked about their diets, and blood was collected. Women who had the highest intakes of soy protein (11 grams, the equivalent of 3 ounces of tofu and 1/3 cup soymilk) had the lowest total cholesterol and LDL-cholesterol (bad cholesterol) levels. Many of these women were either vegan or vegetarian. Women with a soy protein intake of six or more grams per day had a 12 percent lower LDL-cholesterol level than women who ate less than half a gram per day of soy protein. The authors of this study conclude, “moderate intakes of soy foods as part of a regular diet are associated with favorable blood cholesterol concentrations. This may be partly due to a biological effect of soy and partly due to the overall composition of diets with a high soy content.”

Rosell MS, Appleby PN, Spencer EA, Key TJ. 2004.

Soy intake and blood cholesterol concentrations: a cross-sectional study of 1033 pre- and postmenopausal women in the Oxford arm of the European Prospective Investigation into Cancer and Nutrition. Am J Clin Nutr 80:1391-96.

Soy and Breast Cancer

Breast density, as measured by mammography, is a predictor of breast cancer risk. Women with high breast densities are reported to be four to six times more likely to develop breast cancer. Many factors influence breast density, including genetics, medications, and diet. Some studies have found that soy intake was associated with greater breast density, but results have been inconclusive. A recent large study had 109 women eat two servings of soy, providing 50 milligrams of isoflavones, every day for two years. These women were compared to a control group of 111 women who were instructed not to increase their soy intake, which was very low. After two years, there was no significant difference in breast density between the two groups. This suggests that soy consumption in adulthood does not increase breast density. This study did find that Caucasian women who reported eating more soy during their lives had a higher breast density, while women who ate soy at least weekly after they were 20 years old (but ate little soy before that) had a greater reduction in breast density during this study. Further study is needed to evaluate the role of soy intake during childhood and adolescence on breast cancer risk. The results of this study, however, suggest that moderate soy consumption by adult women has little effect on breast density and does not appear to increase risk of breast cancer.

Maskarinec G, Takata Y, Franke AA, et al. 2004.

A 2-year soy intervention in premenopausal women does not change mammographic densities. J Nutr 134:3089-94.

Neuhouser ML. 2004.

Soy mammographic breast density: plausible hypothesis but limited evidence in humans. J Nutr 134:2911-12.

Milk and Ovarian Cancer

Ovarian cancer is the fourth most common cause of cancer death among women. Several studies have suggested a link between dairy products or milk and ovarian cancer. The fact that Sweden has one of the highest rates of ovarian cancer in the world and that the Swedish population consumes a variety of dairy products led Swedish researchers to investigate the relationship between cow’s milk and ovarian cancer. They studied more than 60,000 women for an average of 13.5 years. During that time, 266 women developed ovarian cancer. Women who consumed four or more daily servings of dairy products had twice the risk of developing one type of ovarian cancer compared to women who consumed less than two servings. Milk was the dairy product with the strongest association with ovarian cancer. Again, twice the risk was seen in women drinking two or more glasses of cow’s milk a day compared to women who seldom or never drank cow’s milk. Lactose, the naturally occurring sugar found in milk, was also associated with risk; each 10-gram per day increase in lactose (equivalent to about one glass of cow’s milk) was associated with a 20 percent greater risk of one type of ovarian cancer. Some researchers have speculated that galactose, a component of lactose, might be the culprit in dairy products. Soymilk does not contain lactose or galactose and is certainly a simple alternative to cow’s milk.

Larsson SC, Bergkvist L, Wolk A. 2004.

Milk and lactose intakes and ovarian cancer risk in the Swedish Mammography Cohort. Am J Clin Nutr 80:1353-57.

Whole Grains and Fruits Protect Against Weight Gain in Men

Diets that include generous amounts of whole grains have been associated with a reduced risk of heart disease, stroke, type 2 diabetes, and some cancers. Whole grain fans will be happy to hear that whole grains can also protect against the seemingly inevitable weight gain that occurs with aging. A study, lasting 8 years, was conducted on more than 27,000 men aged 40-75 years. Periodically, the men were asked about their food choices and their weight. For every 40-gram (a little more than an ounce) a day increase in whole grains, men gained half a pound less than men who did not increase their intake of whole grains. If bran was added to their diet or included in fortified foods, weight gain was reduced even more. Fruit fiber also appeared to protect against weight gain. For every 20-gram (less than an ounce) increase in fruit fiber, the men gained 5 pounds less. Even something as simple as adding a single apple to their diets every day resulted in men gaining 1-1/2 pounds less over the 8-year study. So, eat more whole grain cereals, popcorn, brown rice, and fruits (instead of refined grains and greasy snacks) if you want to avoid gaining extra weight as you age.

Koh-Banerjee P, Franz M, Sampson L, et al. 2004.

Changes in whole-grain, bran, and cereal fiber consumption in relation to 8-y weight gain among men. Am J Clin Nutr 80:1237-45.