Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

By Reed Mangels, PhD, RD, FADA

Soymilk As An Option for School Lunches

What would happen if elementary school children were given a choice of soymilk along with cow’s milk in the school cafeteria? That’s what researchers with the Physicians Committee for Responsible Medicine aimed to find out in a study in three elementary schools in southern Florida. Approximately a third of the students were Hispanic and a third were African-American. The remainder were white, multiracial, or Asian in ethnicity.

For the 4-week study period, single-serve cartons of calcium-fortified vanilla and chocolate soymilk were placed in the lunch line cooler along with cartons of cow’s milk. Before that, the children had a chance to sample the soymilk. At the end of the four-week trial, close to a quarter of the students were choosing soymilk, while three-quarters chose cow’s milk. Prior to the introduction of soymilk, approximately 79 percent of students chose a calcium-rich beverage with lunch. This increased to 83 percent after soymilk was introduced, possibly because some students who didn’t want to drink cow’s milk because of lactose intolerance, allergy, or other reasons now had an alternative. This study illustrates that many children will choose enriched soymilk if it is offered as a part of school lunch. Unfortunately, the National School Lunch Program does not reimburse schools if they serve soymilk in place of cow’s milk without a doctor’s request.

Reilly JK, Lanou AJ, Barnard ND, et al. 2006.

Acceptability of soymilk as a calcium-rich beverage in elementary school children. J Am Diet Assoc 106:590-93.

Expert Panel Evaluates Soy Safety

In March 2006, the Center for the Evaluation of Risks to Human Reproduction, a part of the National Institutes of Health, called together a panel of 14 scientific experts to examine soy formula and genistein, a substance found in soy. The panel was convened in part because of public concerns about the effects of genistein and soy formula on infant and child development. The panel reviewed and evaluated scientific research to determine if either soy formula or genistein causes problems with reproduction or with development.

Genistein is a phytoestrogen, a substance found in soy that has properties like the hormone estrogen. Infants receiving soy formula have a higher intake of genistein and of soy per pound of body weight than any other group. Certainly, if problems were seen in infants receiving soy formula, many vegetarian families who use soy frequently would also have a reason to be concerned.

After an extensive review of the existing research, the panel concluded that there was little or no reason to be concerned about the safety of genistein for infants using soy formula. Adverse effects have not been observed at intake levels below 35 milligrams of genistein per kilogram body weight. Total genistein intake of infants using soy formula is 8 milligrams per kilogram or less, considerably below the levels that appear to cause problems. Adult intake of genistein is usually less than 1 milligram per kilogram, even in groups who eat soy regularly, such as vegetarians and the Japanese. Similarly, based on current research, use of soy formula does not appear to lead to developmental or reproductive problems. The panel urged that additional research be conducted to provide more information about the safety of soy and its components.

Overweight and obesity are major health problems, not just in the United States but worldwide. More than 60 percent of adults in the United States are overweight, and 30 percent are obese. Worldwide, more than 1.2 billion people are overweight or obese. Vegetarians tend to have lower body weights than non-vegetarians. A review of the scientific literature found that 29 out of 40 studies of vegetarians showed that vegetarians weighed significantly less than non-vegetarians. This was true for both men and women, for African Americans, Nigerians, Asians, and other groups. Nine small studies also showed that vegetarians weighed less than non-vegetarians, but the difference was not statistically significant.

Vegetarian women average between 6 and 23 pounds lighter than non-vegetarian women, while vegetarian men are an average of 10 to 28 pounds lighter. Generally, vegans have the lowest body weights, followed by lacto-ovo vegetarians, then by near vegetarians (eating meat or fish less than once a week) with meat eaters having the highest weights, on average. These differences in weight persist even when cigarette smoking is controlled for. Possible explanations for weight differences include lower calorie and fat intakes and higher fiber intakes by vegetarians. Vegetarian diets have also been successfully used for weight reduction.

Berkow SE, Barnard ND. 2006.

Vegetarian diets and weight status. Nutr Rev 64:175-88.

Dietary Treatment for Elevated LDL Cholesterol Levels

David Jenkins and other researchers at the University of Toronto made news when they found that, under carefully controlled conditions, a near-vegan diet was as effective as medication at lowering LDL (bad) cholesterol levels in people at risk for heart disease. The researchers recently tested a similar diet for a 1-year period in free-living subjects. All subjects had high blood cholesterol levels. Study subjects were instructed about a diet that was high in soy protein, almonds, plant sterols, and fiber from foods like oats, barley, psyllium, eggplant, and okra. Subjects were encouraged to eat a vegan diet. If they chose to eat meat or dairy products, they were asked to only use small amounts and to choose foods low in saturated fats and cholesterol. At the end of a year, two out of 55 subjects were following a vegan diet and five were following a lacto-ovo vegetarian diet. The other subjects ate limited amounts of meat and fish with approximately 5 percent of calories coming from animal protein. Significant reductions were seen in LDL cholesterol levels that, for many participants, were similar to what would be expected with statins (a type of medication that lowers blood lipid levels). HDL (good) cholesterol levels increased slightly, and triglyceride levels decreased. These good results were seen even in subjects who were already eating a low-saturated fat, low-cholesterol diet before the study started. This study suggests that a vegan or near-vegan diet featuring specific cholesterol-lowering foods can be an alternative to medication for some people with high blood cholesterol levels. Of course, this should be discussed with your health care provider before altering medication.

Jenkins DJA, Kendall CWC, Faulkner DA, et al. 2006.

Assessment of the longer-term effects of a dietary portfolio of cholesterol-lowering foods in hypercholesterolemia. Am J Clin Nutr 83:582-91.

Zinc for Vegetarians

Vegetarian sources of zinc include dried beans, soy products, nuts and seeds, enriched cereals, wheat germ, and whole grains. Many of these foods also contain phytic acid, a substance that binds with zinc and reduces the amount absorbed. Because of this reduced absorption from plant foods, recommendations call for higher zinc intakes by vegetarians whose diets are high in grains and dried beans. Dietary protein, especially animal protein, is believed to reduce the effect of phytic acid on zinc absorption. A recent study determined the amount of zinc absorbed from a vegetarian diet compared to a non-vegetarian diet; both diets were comparably high in phytic acid. The vegetarian diet was much lower in protein and zinc. Subjects absorbed approximately 25 percent of the zinc, whether they were on the vegetarian or the non-vegetarian diet. This study suggests that anyone, whether vegetarian or not, whose diet is high in phytic acid will need additional zinc to offset the effects of phytic acid and that meat did not markedly increase the amount of zinc absorbed.

Kristensen MB, Hels O, Morberg CM, et al. 2006.

Total zinc absorption in young women, but not fractional zinc absorption, differs between vegetarian and meat-based diets with equal phytic acid content. Br J Nutr 95:963-67.