Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
Soy Foods Improve Breast Cancer Survival Rates
Soy foods are rich in compounds called phytoestrogens that resemble the hormone estrogen. Since estrogen appears to play a role in breast cancer development and progression, is it safe for women with breast cancer to consume soy? A recent large study examined soy food intake in women in China with breast cancer and evaluated the association of soy foods with cancer recurrence and with death. More than 5,000 women who had been diagnosed with breast cancer were studied for an average of four years after diagnosis. Women who ate the most soy foods had almost a 30 percent lower risk of death during the period studied and were significantly less likely to have a recurrence of breast cancer compared to women eating the lowest amount (5 grams of soy protein or less per day) of soy foods. These results were similar for both estrogen-receptor positive and estrogen-receptor negative cancer. The use of a common breast cancer drug, Tamoxifen, did not change results. Intakes of more than 11 grams of soy protein, or more than 40 milligrams of soy isoflavones, did not appear to offer additional protection. Women in this study mainly ate traditional soy foods, such as tofu, miso, soybeans, and soymilk, rather than using soy supplements, fake meats, or isoflavone supplements. In other words, it looks as if a moderate intake of traditional soy foods is both safe and beneficial for women with breast cancer.
Shu XO, Zheng Y, Cai H, et al. 2009. Soy food intake and breast cancer survival. JAMA 302(22):2437-43.
Growing Up Too Soon?
The average age at which puberty starts has dropped significantly over the past 150 years. Many factors affect the timing of the start of puberty, and one appears to be dietary protein intake in childhood. A study of more than 100 boys and girls in Germany found that children with a higher animal protein and/or a higher dairy protein intake at ages 3-4 or 5-6 years had an earlier start of puberty than did children with lower protein intakes. A higher vegetable protein intake was associated with a later onset of puberty. This agrees with some earlier studies that found vegetarian girls matured slightly later than non-vegetarian girls. An earlier puberty has been related to an increased risk of certain cancers, including breast cancer. For example, each additional year older a girl is at menarche (onset of menstrual periods) is associated with a 9 percent lower risk of breast cancer. The results of this study suggest a potential health benefit of vegan diets in childhood.
Günther ALB, Karaolis-Danckert N, Kroke A, et al. 2010. Dietary protein intake throughout childhood is associated with the timing of puberty. J Nutr 140:565–71.
Vegan Diets on the Job
Imagine this. A major U.S. corporation offers employees a worksite nutrition program featuring a lowfat vegan diet. Think you're dreaming? You're not. This really happened at GEICO headquarters in Chevy Chase, Maryland. The 22-week program was offered to employees who were overweight and/or had type 2 diabetes. The 65 participants who volunteered for the study were asked to follow a lowfat vegan diet that included vegetables, fruits, grains, and beans. No restrictions were placed on portion sizes or calories. The cafeteria offered one breakfast item, two lunch entrées, and two side dishes daily that met the diet guidelines. Participants were encouraged to attend weekly lunchtime support sessions. A comparison group consisted of 44 similar employees in another office who continued with their usual diet. Study participants lost weight, had lower blood pressure, and had fewer absences than the comparison group. Diet records showed that study participants were able to reduce dietary total fat, saturated fat, trans fat, cholesterol, and calories. They increased their intake of many important nutrients, including fiber, vitamin C, potassium, and vitamin A. The researchers who conducted this study conclude, "With education on the use of lowfat vegan diets and modest worksite support, employees can implement changes in their diets that, if sustained, may reduce the risk of common and costly diseases such as heart disease, cancer, and diabetes."
Levin SM, Ferdowsian HR, Hoover VJ, et al. 2010. A worksite programme significantly alters nutrient intakes. Public Health Nutr Jan 15:1-7. [Epub ahead of print].
Agricultural Policy - A New Way to Fight Obesity?
A recent article looks at an interesting way to combat obesity, by changing agricultural policy. Americans are eating more calories than they did 40 years ago when rates of obesity were lower. These extra calories are mainly from added fats and sugars and from refined grains. American farms are the source for many of these extra fats, sugars, and calories in forms like high-fructose corn syrup and soy oil.
Over the long term, what farmers grow is heavily influenced by agricultural policy. For 35 years, commodity farmers (those growing corn, wheat, cotton, rice, milk, and later soybeans) have been encouraged by a federal 'cheap food' policy to produce as much as possible of a few crops. The result is that, not only are many more fats, sugars, and calories available, but also that foods containing fats and sugars cost less than many healthier foods. What about fruits and vegetables? USDA data indicate that the U.S. food system does not produce enough fruits or vegetables to meet the recommended intake levels for these foods. We could import more of these foods, but that can be problematic in terms of energy use and food safety concerns. U.S. agricultural policy generally has not offered incentives or supported farmers to grow fruits and vegetables. The article's author calls for a redesign of the food environment in the United States, including a significant change in agricultural policies. Stay tuned for the 2012 Farm Bill, which offers opportunities to change agricultural policies in an effort to fight obesity.
Wallinga D. 2010. Agricultural policy and childhood obesity: a food systems and public health commentary. Health Aff (Millwood) Mar-Apr 29(3): 405-10.
The Latest News on Protein and Bone Health
Our bones contain both calcium and protein, and both are needed to make strong bones. On the other hand, high dietary protein may increase calcium losses in urine, potentially leading to weaker bones. A recent meta-analysis examined the relationship between dietary protein and bone health. Higher dietary protein intakes appeared to have a slight positive effect on bone strength but had little effect on the risk of breaking a bone. Results were similar regardless of the protein source— higher intakes of total protein, animal protein, or vegetable protein all had little effect on bone health. These results raise questions about the belief that highprotein diets are harmful to bone. Everyone—vegan, vegetarian, or non-vegetarian—should strive to get adequate protein and calcium for optimal bone health.
Millward DJ, Torgerson DJ, Hewitt CE, Lanham- New SA. 2009. Dietary protein and bone health: a systematic review and meta-analysis. Am J Clin Nutr 90:1674-92.
Kerstetter JE. 2009. Dietary protein and bone: a new approach to an old question. Am J Clin Nutr 90:1451-52.
PBDEs and Diet
Polybrominated diphenyl ethers (PBDEs) are flame retardants that are used in electronics and fabrics. Because of their widespread use, PBDEs are found in dust, in the air, and in food. Although only a few studies have been done on the effects of PBDEs in humans, harmful effects on male hormones and fertility, thyroid function, and birth weight of infants have been reported. A large study in the United States measured blood levels of PBDES and asked participants about their diet. The lowest concentrations of PBDEs were seen in those who ate red meat and poultry less than once a week or who did not eat meat at all. Separate results were not presented for vegetarians because they only represented a small number of subjects, so they were included in the group of low meateaters. The group of low meat-eaters had blood PBDE levels that were approximately 25 percent lower than those who ate more meat. Both poultry and red meat were associated with higher PBDE levels. Although this study did not find an association between fish or dairy products and blood PBDE levels, other studies have found high levels of PBDEs in fish and an association between PBDEs in breastmilk and dairy fat intake.
Fraser AJ, Webster TF, McClean MD. 2009. Diet contributes significantly to the body burden of PBDEs in the general U.S. population. Environ Health Perspect 117(10):1520-25.
