Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
By Reed Mangels, PhD, RD, FADA
The ADA and Dietitians of Canada Publish a New Position Paper on Vegetarian Diets
The American Dietetic Association (ADA) and Dietitians of Canada (DC) published their updated position on vegetarian diets in the June 2003 Journal of the American Dietetic Association. This paper features an extensive review of vegetarian diets, including consumer trends; statistics on new products; health benefits of vegetarian diets; updates on protein, iron, zinc, calcium, vitamin D, riboflavin, vitamin B12, vitamin A, omega-3 fatty acids, and iodine for vegetarians; use of vegetarian diets throughout the life-cycle; the role of vegetarian diets in prevention and treatment of chronic diseases, such as obesity, heart disease, high blood pressure, diabetes, cancer, osteoporosis, and renal disease; and the use of vegetarian diets in federal programs like School Lunch, the Elderly Nutrition Program, corrections facilities, and the armed forces. Specific suggestions for dietitians who work with vegetarian clients are included. The complete position paper is a helpful source of information for the media, health care professionals, and others with questions about vegetarianism.
Mangels AR, Messina V, Melina V. 2003. Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets. J Am Diet Assoc 103:748-65.
New Vegetarian Food Guide
A paper that presents a new food guide for vegetarians accompanies the ADA/CD Position Paper on Vegetarian Diets. This new food guide is presented both as a pyramid and as a rainbow, the form used in Canada. The guide can be adapted for different types of vegetarian diets and includes a wide variety of foods commonly used by vegetarians. Foods are divided into groups in this food guide. Besides the more common groups of Grains, Vegetables, and Fruits, this guide features a Legumes, Nuts, and Other Protein-Rich Foods group; a Fat group; and a Calcium-Rich Foods group. The Calcium-Rich Foods group includes a variety of vegetarian sources of calcium and includes foods from each of the other food groups. Both adults and children can use this vegetarian food guide.
Messina V, Melina V, Mangels AR. 2003. A new food guide for North American vegetarians. J Am Diet Assoc 103:771-5.
High Protein Diets and Kidney Function
High protein diets are popular once again, with supporters claiming that they promote weight loss. Two recent studies suggest that, at least for some people, high dietary protein can have harmful effects on kidney function. In the first study, researchers from Harvard University looked at protein intakes of more than 1,600 older women. They also evaluated the women's kidney function using a measurement called the glomerular filtration rate, or GFR. Dietary protein had no significant effect on kidney function in women who had normal kidney function at the start of this study. However, in women with mild impairment of kidney function, a higher total protein intake (median of 92 grams per day, compared to 61 grams per day) was associated with a faster decline in kidney function. This was especially true for protein from meat, fish, poultry, and eggs. These results certainly suggest that women with some impairment of kidney function should avoid high protein diets and that there may be some advantage to use of plant proteins as compared to animal proteins. The second study looked at both men and women, aged 20 to 80 years. This time microalbuminuria was measured. Microalbuminuria refers to a small increase in albumin, a protein, in the urine and indicates a problem with kidney function. Microalbuminuria is also associated with increased risk of stroke and heart attacks. In people without high blood pressure or diabetes, dietary protein was not associated with microalbuminuria. However, in people with both high blood pressure and diabetes, high levels of dietary protein (average intake of 111 grams per day, or about 24 percent of calories) increased the risk of having microalbuminuria. Unfortunately, results were not separated for animal protein and plant protein, so we don't know if the source of the protein would have any effect on the findings of this study. These results do suggest that people with both high blood pressure and diabetes should consider means other than high protein diets for weight loss.
Knight EL, Stampfer MJ, Hankinson SE, et al. 2003. The impact of protein intake on renal function decline in women with normal renal function or mild insufficiency. Ann Intern Med 138:460-7.
Wrone EM, Camethon MR, Palaniappan L, Fortmann SP. 2003. Association of dietary protein intake and microalbuminuria in healthy adults: Third National Health and Nutrition Examination Survey. Am J Kidney Dis 41:580-7.
Soy and Menopause
Many women choose to use hormone replacement therapy (HRT) to relieve some of the symptoms of menopause like hot flushes (also called hot flashes). Recent reports have led many women to question the safety of HRT and to look for other ways to reduce hot flushes. Soy products have been proposed as an alternative. Mark Messina, PhD, and Claude Hughes, MD, PhD, reviewed 13 studies that tested the effects of soyfoods or soy isoflavones on hot flushes. They found that soyfoods or isoflavone supplements were most effective in women with frequent hot flushes. For example, they estimate that women with 10 hot flushes per day who begin using soyfoods or isoflavones, will, on average, have about 4.5 fewer hot flushes daily.
Women experience a marked increase in the rate of bone loss in the years immediately after menopause. Soy protein appears to help to maintain bones, especially in women who are not using hormone replacement therapy (Arjmandi). Soyfoods and isoflavones may also reduce the risk of heart disease in postmenopausal women. Messina and Hughes recommend that women with frequent hot flushes try using soyfoods or isoflavone supplements that provide around 50 milligrams of isoflavones per day. They recommend an upper limit of 100 milligrams of isoflavones per day.
Messina M, Hughes C. 2003. Efficacy of soyfoods and soybean isoflavone supplements for alleviating menopausal symptoms is positively related to initial hot flush frequency. J Medicinal Food 6:1-11.
Arjmandi BH, Khalil DA, Smith BJ, et al. 2003. Soy protein has a greater effect on bone in postmenopausal women not on hormone replacement therapy, as evidenced by reducing bone resorption and urinary calcium excretion. J Clin Endocrinol Metab 88:1048-54.
Vegetarians and Vegans in the UK
A large study of meat-eaters, fish-eaters, vegetarians (use eggs and/or dairy products), and vegans in Europe is being conducted. More than 500,000 people are participating in this study. A recent report looked at around 65,000 subjects from the United Kingdom.
Here are some of the findings:
- 38 percent of vegan women aged 40 and older had no children; 16 percent of meat-eating women over 40 had no children.
- Meat-eating women aged 50 and older were much more likely to have used hormone replacement therapy than vegan women.
- Vegans were the leanest of the four groups; fish-eaters and vegetarians were intermediate; and meat-eaters had the highest body mass index. Very few vegans were obese.
- Vegans had higher intakes of carbohydrates, polyunsaturated fats, and fiber and lower intakes of protein and saturated fats. Total fat intake was only slightly different among the groups and averaged 31 percent of total calories.
- Vegans had higher intakes of thiamin, folate, vitamin C, vitamin E, and iron and lower intakes of vitamin B12, vitamin D, calcium, and zinc. Vitamin B12 and calcium intake among vegans were below recommendations, although intakes may actually be a bit higher because some fortified foods may not have been included in the analysis and supplements were not included.
The subjects of this study will be followed for the next 10 years to see if diet affects risk of cancer and other conditions.
Davey GK, Spencer EA, Appleby PN, et al. 2003. EPIC—Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33,883 meat-eaters and 31,546 non meat-eaters in the UK. Public Health Nutr 6:259-68.
