Scientific Update
By Reed Mangels, PhD, RD, FADA
Use of a Lacto-ovo Vegetarian Diet for 8 Weeks Has Little Effect on Blood
Iron Indexes
The type of iron in vegetarian diets is called non-heme iron. Non-heme iron is less
well absorbed than heme iron, the type of iron found in meat. Does this difference
have an effect on iron status?
Researchers at USDA studied 21 young women. The subjects were placed on lacto-ovo vegetarian diets for 8 weeks and non-vegetarian diets for 8 weeks. The subjects were not vegetarian before the study started.
Non-heme iron was less well absorbed from the vegetarian compared with the non-vegetarian diets (1.1% absorbed compared with 3.8%). This was believed to be due to the absence of meat which enhances non-heme iron absorption and to substances in the vegetarian diet (like phytate) which interfere with iron absorption. Subjects eating vegetarian diets appeared to compensate to some extent for the lower iron absorption by decreasing iron losses in the stool. This compensation and other unknown factors led to no change in blood indexes of iron status after 8 weeks on a vegetarian diet. Perhaps a longer period of time on a lacto-ovo vegetarian diet would have resulted in poorer iron status. On the other hand, a longer period on a vegetarian diet may lead to increased compensation for poor iron bioavailability.
Hunt, JR; Roughead, ZK. 1999. Nonheme-iron absorption, fecal ferritin excretion, and blood indexes of iron status in women consuming controlled lacto-ovo-vegetarian diets for 8 wks. Am J Clin Nutr 69: 944-952.
Puzzling Results from the Nurses' Health Study
Did you ever hear of the Nurses' Health Study? This is a study of more than 80,000
nurses who have been examined for 23 years. We've reported on this study before in
Vegetarian Journal. This study has given us information suggesting that
trans fats are even worse for the heart than saturated fats, that there is no
relationship between dietary calcium and risk of fractures, that increased total or
animal protein intake may increase the risk of fractures, and much more.
The Nurses' Health Study was in the news recently when researchers reported that there was no association between the intake of dietary fiber and the risk of cancer of the colon and the rectum. These results were surprising for many people. We've all heard that higher-fiber diets reduce the risk of colon cancer. What can we say? The authors speculate that fiber may have an impact early in life and this was not measured in this study. It is also possible that, in order to reduce risk of colon cancer, people may need to eat more than the 30 to 35 grams of fiber a day (more typical of vegetarian diets) which was the maximum subjects in this study ate. This reduction in risk with very high intakes of fiber is not supported by other studies, however. Another possibility is that specific types or components of fiber are important in reducing risk of colon cancer. This study did not examine types or components of fiber.
Do these results mean that it's fine to eat a typical American low-fiber diet? Absolutely not. Even if fiber does not reduce risk of colon cancer, it does appear to reduce risk of heart disease.
Fuchs, CS; Giovannucci, EL; Colditz, GA; et al. 1999. Dietary fiber and the risk of colorectal cancer and adenoma in women. N Engl J Med 340: 169-176.
Potter, JD. 1999. Fiber and colorectal cancer - where to now? N Engl J Med 340: 223-224.
