Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

By Reed Mangels, PhD, RD, FADA

FAO Reports That Livestock is a Major Contributor to Serious Environmental Problems Worldwide

The Food and Agriculture Organization (FAO) of the United Nations recently released an extensive report assessing livestock's impact on the environment. Livestock production was shown to have a serious effect on land degradation, climate change, air pollution, water shortage and pollution, and the loss of biodiversity. The report's conclusions were sobering:

  • Global production of meat is expected to more than double over the next 50 years. In 2003, average yearly meat consumption in the U.S. was 271 pounds per person; in India, it was 11 pounds per person.
  • Livestock production accounts for 30 percent of the land surface of the earth and 70 percent of agricultural land.
  • The livestock sector is responsible for a greater production of greenhouse gas than automobiles and other forms of transportation. Livestock also produce almost two-thirds of ammonia emissions, a significant contributor to acid rain.
  • More than 8 percent of human water use is due to the livestock sector, mainly irrigating feedcrops.
  • In the United States, livestock are responsible for 55 percent of erosion and sediment, 37 percent of pesticide use, and 50 percent of antibiotic use.
  • Most of the world's threatened species are suffering from habitat loss, due -- at least in part -- to livestock production.

Surprisingly, there is little mention of vegetarianism in this report. It does say, "Environmental damage by livestock may be significantly reduced by lowering excessive consumption of livestock products among wealthy people."

The report states that the majority of environmentalists and policymakers do not fully appreciate the enormous effect of livestock production on climate, biodiversity, and water. Perhaps, this report will increase awareness and support the idea that livestock production should rank as a leading focus for environmental policy.

This report is a must-read for those who are concerned about the environment. It can be accessed at

Steinfeld H, Gerber P, Wassenaar T, et al. Livestock's Long Shadow -- Environmental Issues and Opinions. Rome: FAO, 2006.

Milk Linked to Acne in Teenage Girls

Up to nine out of 10 teens have acne. For some, it is a serious physical problem with impacts on social life and self-image. All sorts of foods have been suggested to cause acne -- chocolate, pizza, French fries -- and the list could go on and on. There is little firm evidence to support a role for many of these foods, however.

A recent study identifies a new and somewhat surprising culprit -- milk. Researchers examined more than 6,000 girls and asked them questions about their diet, if they had acne, and how severe it was. Regardless of the type of cow's milk they chose (whole, lowfat, skim, or chocolate), girls who drank two or more glasses a day had a higher risk of acne than did girls drinking less than a glass per week. Other foods, including cheese, chocolate candy, and pizza, were not associated with acne, nor was dietary fat or vitamin D. Not enough girls drank soymilk for it to be evaluated.

Adebamowo CA, Spiegelman D, Berkey CS, et al. 2006. Milk consumption and acne in adolescent girls. Derm Online J 12(4):1.

Motivations for Choosing a Vegetarian Diet

Some have suggested that there is a sub-group of vegetarians (mostly women) who choose a vegetarian diet mainly to lose weight. In a few cases, vegetarian diets have been associated with eating disorders like anorexia nervosa. One problem is that a number of studies examining eating behavior have combined so-called 'semi-vegetarians' (eating chicken and/or fish) and vegetarians (not eating any meat, chicken, or fish) into one group identified as 'vegetarian.' Researchers from the University of Colorado hypothesized that 'semi-vegetarians' and true vegetarians might have different motivations and eating behaviors. They studied 90 young women, of whom 54 were non-vegetarian, 16 ate chicken and/or fish (identified as 'semi-vegetarian'), and 20 consistently followed a vegetarian diet. They examined the women's motivation for food choice and their dietary restraint (whether they consciously monitored what they ate for weight control purposes).

Vegetarians were more likely than 'semi-vegetarians' to say that ethical and/or political reasons were a primary motivation for their food choices. 'Semi-vegetarians' were more likely to be motivated by weight concerns. Both 'semi-vegetarians' and non-vegetarians had higher levels of dietary restraint than did vegetarians. The researchers conclude that the higher levels of dietary restraint seen in 'semi-vegetarians' suggest that they are at higher risk for harmful eating disorders than the vegetarian women. This study illustrates the importance of differentiating between true vegetarians and 'semi-vegetarians' when examining eating behaviors.

Curtis MJ, Comer LK. 2006. Vegetarianism, dietary restraint and feminist identity. Eating Behav 7:91-104.

Reducing Breast Cancer Risk

Every year, more than 200,000 women in the United States are diagnosed with breast cancer. Breast cancer is the number one cause of cancer death in Hispanic women and the second most common cause of cancer death in other women.

There are some things that women can do to reduce their risk of breast cancer. Exercising regularly, maintaining a healthy weight, and limiting alcohol intake have all been shown to reduce risk. A recent study suggests that markedly reducing or eliminating red meat can also reduce breast cancer risk. This study examined more than 90,000 premenopausal women and found that those women who had the highest intakes of red meat (more than 11/2 servings per day) had close to twice the risk of breast cancer as did women eating three or fewer servings of red meat per week. Beef, pork, hamburgers, hot dogs, and processed meats like salami and bologna all appeared to increase risk for a common form of breast cancer called estrogen receptor-positive breast cancer. Maybe this study will be a wake-up call for young and middle-aged women who want to reduce their risk of breast cancer.

Cho E, Chen WY, Hunter DJ, et al. 2006. Red meat intake and risk of breast cancer among premenopausal women. Arch Intern Med 166:2253-59.

Fruits and Vegetables Play a Role in Reducing Gallbladder Removal Surgeries in Women

Diets high in fruits and vegetables have been shown to reduce the risk of heart disease, cancer, and osteoporosis and may also decrease gallbladder surgeries in women. Unfortunately, gallbladder disease is a common illness of adults, affecting women more often than men. Each year, more than 800,000 Americans have their gallbladders removed. A recent study examined the relationship between intake of fruits and vegetables and the rate of gallbladder removal surgeries in women.

In 1976, 121,700 female nurses aged 30 to 55 completed the first Nurses Health Study questionnaire. Every two years until 2000, a follow-up questionnaire was sent to update information that was used in many studies ranging from cancer to cardiovascular health. For this study, researchers used data from 77,090 participants to calculate intake of fruits, vegetables, fiber, and specific vitamins and minerals. Data regarding gallbladder surgeries were also collected.

Women whose diets were the highest in green leafy vegetables, citrus fruits, and vitamin C-rich foods (more than 30 milligrams vitamin C per serving) were less likely to have their gallbladder removed. This is most likely due to diets high in fiber and antioxidants. High fiber diets stimulate bowel movement and reduce bile storage in the gallbladder. Antioxidant vitamins, such as vitamin C, and various minerals (especially magnesium) show a protective effect on gut health. For women, this research suggests a positive relationship between a diet high in fiber, fruits, and vegetables and a reduced rate of gallbladder surgeries. While no single food can lower risk for gallbladder removal, everyone can benefit from a diet containing a variety of fruits and vegetables.

Tsai CJ, Leitzmann MF, Willett WC, Giovannucci EL. 2006. Fruit and vegetable consumption and risk of cholecystectomy in women. Am J Med 119(9): 760-67.

*The article above was reviewed by Stephanie Gall, MS, VRG Dietetic Intern.