Scientific Update
By Reed Mangels, PhD, RD
Most Recent Edition of Dietary Guidelines Mentions Vegetarianism
The Dietary Guidelines for Americans represent a statement of current federal policy on the role of dietary factors in health promotion and disease prevention. The US Departments of Agriculture (USDA) and Health and Human Services (HHS) issue these guidelines. They were first issued in 1980 and have been revised every five years. The 1995 edition had much information about vegetarianism. The latest edition mentions vegetarianism, but not as extensively. It says, "Vegetarian diets can be consistent with the Dietary Guidelines for Americans, and meet Recommended Dietary Allowances for nutrients." Calcium sources are listed for those who do not use dairy products and include soy-based beverages with added calcium, tofu prepared with calcium, greens, and fruit juice with added calcium. For the first time, soy-based beverages with added calcium are listed as a food in the Milk Group of the Food Guide Pyramid, making the Pyramid more useful for vegans. Vegetarian sources of iron are also listed.
The Dietary Guidelines and related information can be downloaded from the USDA's website, located at www.usda.gov/cnpp, or through the HHS Office of Disease Prevention and Health Promotion, at www.health.gov/dietaryguidelines. Printed copies can be purchased by sending a check or money order for $4.75 to Consumer Information Center, Pueblo, CO 81009.
Recommendations for Preventing Heart Disease in Women
Results from a study of more than 84,000 women participating in the Nurses' Health Study indicate that lifestyle and diet can markedly affect a woman's risk of heart disease. Specifically, those women who were not currently smoking; whose weight was appropriate for their height; who engaged in moderate to vigorous physical activity for at least half an hour per day, on average; who ate a diet high in cereal fiber, polyunsaturated fat, folate, and fatty acids from fish, and low in trans fats and glycemic load (foods which raise blood glucose levels); and who drank at least half a drink of an alcoholic beverage daily had the lowest risk of heart disease. A vegetarian diet can easily include all of these behaviors with the exception of eating fatty acids from fish. Dietary factors were grouped together in this study so that it is not possible to tell what the effect of not including fish oil in an otherwise healthful diet would be. We suspect that results would not be markedly different if the diet included polyunsaturated fats (like flaxseed oil, canola oil, and soy oil) that can be used by our bodies to produce the same fatty acids found in fish.
Stampfer MJ, Hu FB, Manson JE, et al. 2000. Primary prevention of coronary heart disease in women through diet and lifestyle. N Engl J Med 343:16-22.
Effect of Different Types of Carbohydrate On Heart Disease Risk
We've all heard that a lowfat diet is good for our hearts. However, if we restrict our dietary fat, we typically compensate by consuming more dietary carbohydrate. Perhaps this is not the best thing.
High intakes of some types of carbohydrate can raise blood triglyceride levels and also appear to reduce the level of HDL (good) cholesterol. A study of more than 75,000 women suggests that carbohydrates with a high glycemic index are associated with an increased risk of heart disease, mainly in women who are overweight. Foods with a high glycemic index are those which are rapidly digested and absorbed and which lead to heightened blood glucose levels after eating them. They include short-grain rice, bread (both white and wheat), breakfast cereals (except for bran cereal), and potatoes. Fruits, vegetables, and dried beans appear to have a low glycemic index. Certainly weight control is important in preventing heart disease, and for those who are already lean, glycemic index may not be relevant. However, for those who are above ideal weight, there may be some advantage to consuming more foods with a low glycemic index like legumes, fruits, and vegetables.
Liu S, Willett WC, Stampfer MJ, et al. 2000. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr 71:1455-1461.
Blix G. 2000. The glycemic index: irrelevant indicator or indispensable instrument? Issues in Vegetarian Dietetics IX:1, 5-9.
How Much Calcium Do We Really Need?
Have you ever wondered if you need less calcium because you are a vegetarian and because your diet is lower in protein and sodium? Christopher Nordin, a scientist with the Institute of Veterinary Science in Adelaide, Australia, raises the issue of varying calcium needs in an opinion piece in a publication for nutrition scientists. Certainly there are genetically determined differences in calcium need. Nordin points out that the amount of calcium needed "varies not only from individual to individual, but from culture to culture" so that there can be no single, universal calcium requirement. He calls for those groups making recommendations to take this into consideration, which is something the US has not done at this point.
Nordin BEC. 2000. Calcium requirement is a sliding scale. Am J Clin Nutr 71:1381-1383.
Soy Isoflavones Help to Control Cholesterol Levels
Isoflavones are substances found in plant foods, including soy products, which have an estrogen-like effect. Researchers at several universities recently fed 13 women varying levels of soy isoflavones and measured the effect on the women's blood cholesterol levels. At the beginning of the study, the women had blood cholesterol levels that were within the normal range. The high-isoflavone diet (around 129 milligrams of isoflavones per day) lowered LDL cholesterol by 8-10% and improved the lipid profile. This is not a large change in LDL cholesterol levels, but, over a lifetime, the improvement in blood lipid levels could help to reduce risk of heart disease.
Merz-Demlow BE, Duncan AM, Wangen KE, et al. 2000. Soy isoflavones improve plasma lipids in normocholesterolemic premenopausal women. Am J Clin Nutr 71:1462-1469.
