Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

by Reed Mangels, PhD, RD, FADA

News from the Fourth International Congress on Vegetarian Nutrition

In August 2002, The Fourth International Congress on Vegetarian Nutrition was held in Loma Linda, CA. More than 400 people from over 40 different countries attended this congress to learn about recent research on vegetarianism. The proceedings of this congress were published in a 170-page supplement to the American Journal of Clinical Nutrition. Here are a few reports that seemed especially interesting:

Are Some Vegetarians Really Meat-Free?
Or Do They Just Say They Are?

Researchers from Loma Linda University used data from a large survey of people in the United States conducted by the USDA. One survey question asked if respondents considered themselves to be vegetarian. Of the 13,313 respondents, 334 considered themselves vegetarians. Respondents kept a record of what they ate for two days. When these records were examined, only 120 people who defined themselves as vegetarian actually did not eat meat, fish, or poultry. The diets of those who did not eat meat were different, nutritionally speaking, from those who did eat meat. This study shows how important it is for researchers and dietitians to clarify what someone means when they say they are vegetarian.

Haddad EH, Tanzman JS. 2003. What do vegetarians in the United States eat? Am J Clin Nutr 78 (suppl):626S-32S.

Iron and Zinc Rarely a Problem for Western Vegetarians

Janet Hunt, a noted researcher on iron and zinc, concluded that adverse health effects from lower iron and zinc absorption in vegetarians living in developed countries have not been demonstrated. She recommended monitoring iron status of vegetarian children and premenopausal women and prescribing iron supplements only when iron deficiency is seen.

Hunt JR. 2003. Bioavailability of iron, zinc, and other trace minerals from vegetarian diets. Am J Clin Nutr 78 (suppl):633S-39S.

Achieving Optimal Fatty Acid Status

Vegetarian diets are often low in some key fatty acids like DHA, EPA, and alpha-linolenic acid. A session at the congress presented guidelines for achieving optimal fatty acid status in vegetarians. These include eating a variety of whole plant foods; getting most fat from whole foods like olives, nuts, seeds, and soy foods; selecting olive, canola, and nut oils for cooking; limiting intake of processed foods and deep-fried foods; choosing foods rich in alpha-linolenic acid like flaxseed, flaxseed oil, hempseed oil, walnuts, canola oil, and soy products; and considering use of a DHA supplement derived from microalgae.

Davis BC, Kris-Etherton PM. 2003. Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications. Am J Clin Nutr 78 (suppl):640S-46S.

Environmental Impact of Various Diets

One symposium focused on the ecologic and environmental impacts of different diets. Claus Leitzmann, a German researcher, concluded that “vegetarian diets are well suited to protect the environment, to reduce pollution, and to minimize global climate changes.” He recommended using organically grown, regionally produced, in-season food.1 Two researchers from Cornell University analyzed the use of land and energy resources needed for a meat-based diet compared to a lacto-ovo vegetarian diet. The meat-based diet required more energy, land, and water resources.2 Researchers from The Netherlands and the United States also found an environmental advantage to vegetarian diets. They report, however, that a vegetarian diet consisting mainly of exotic foods transported long distances by plane, frozen vegetables, or vegetables grown in fossil fuel-heated greenhouses may lead to a greater environmental burden than that of locally produced organic meat.3

1 Leitzmann C. 2003. Nutrition ecology: the contribution of vegetarian diets. Am J Clin Nutr 78 (suppl):657S-59S.

2 Pimentel D, Pimentel M. 2003. Sustainability of meat-based and plant-based diets and the environment. Am J Clin Nutr 78 (suppl):660S-63S.

3 Reijnders L, Soret S. 2003. Quantification of the environmental impact of different dietary protein choices. Am J Clin Nutr 78 (suppl):664S-68S.

Soft Drinks + Fast Food—Do They Add Up to Fat Kids?

Childhood obesity in the United States is at an all-time high. Nearly one-third of children are overweight or close to being overweight. Overweight kids often have higher blood pressure and cholesterol and are at risk for diabetes. These are problems that lead to additional health problems in adulthood. Everyone seems to be asking, “Why are we seeing so many overweight children?” A recent commentary attempted to address this question. One answer may be the tremendous increase in foods eaten away from home. In the past 20 years, there has been a 300 percent increase in the proportion of foods children eat from restaurants and fast food outlets. Another answer is the use of soft drinks. The soft drink intake of teen boys has more than tripled in the past 30 years. Children who drink soft drinks take in close to 200 more calories per day than children who don’t regularly drink soft drinks. School food services often rely on sales of high fat and high sug ar food s to increase revenue. All of these factors appear to have led to the current epidemic of childhood obesity.

St-Onge M-P, Keller KL, Heymsfield SB. 2003. Changes in childhood food consumption patterns: a cause for concern in light of increasing body weights. Am J Clin Nutr 78:1068-73.

Whole-Grain, High-Fiber Foods Help with Weight Control

Walk into any supermarket or pick up any popular magazine, and you’ll see recommendations to eat a low-carb diet to promote weight loss. This issue’s Nutrition Hotline examines many of the fallacies associated with Atkins-type diets. A recent study adds additional support to those questioning recommendations to reduce dietary carbohydrate. Researchers from Harvard University differentiated between diets that are high in carbohydrate from whole grains and high-fiber foods and diets that consist mainly of refined-grain products. They studied more than 74,000 women for 12 years. Their results? Women who ate more whole grains weighed less than women who ate fewer whole grains. Women with the highest intake of dietary fiber had a 49 percent lower risk of major weight gain than did women with the lowest fiber intakes. The bottom line? If you’re trying to control your weight, focus on high-fiber foods like fruit s, vegetables, and whole grains and eat fewer refined-grain products.

Liu S, Willett WC, Manson JE, et al. 2003. Relation between changes in intakes of dietary fiber and grain products and changes in weight and development of obesity among middle-aged women. Am J Clin Nutr 78:920-27.

Eating Fish Can Increase Risk of Breast Cancer

Factors like environmental pollutants and mercury levels in fish have led some to question recommendations to eat more fish to reduce risk of heart disease. A recent study raised another red flag—fish appears to be associated with increased risk of breast cancer in post-menopausal women. More than 23,000 Danish women who were 50-64 years old at the start of the study were followed for close to five years. During the study, 424 women developed breast cancer. When the women were divided into groups based on the amount of fish they reported eating, women who ate more than two ounces of fish per day had a 47 percent higher rate of breast cancer than women eating one ounce of fish or none daily. The fat content of the fish and the way it was prepared did not appear to affect breast cancer risk. This is the first study to show this association, and additional studies are needed to discover what substances in fish led to these results. This study adds weight to the need to rethink recommendations calling for eating more fish.

For more information about recommendations related to fish consumption, see Vegetarian Journal Sept/Oct 2001, American Heart Association Calls for Eating Fish Twice Per Week - What’s a Vegetarian To Do?

Stripp C, Overvad K, Christensen J, et al. 2003. Fish intake is positively associated with breast cancer incidence rate. J Nutr 133:3664-69.