Vegan diet and breast cancer risk. (Scientific update: a review of recent scientific papers related to vegetarianism).

Insulin-like growth factor I, or IGF-I for short, is a hormone that appears to promote the growth of both normal and malignant cells in the breast. Elevated levels of IGF-I in the blood have been associated with an increased risk of developing breast cancer before menopause. Close to 300 British women were studied, 92 of whom were vegan, and 101 vegetarian (used dairy and/or eggs). The average level of IGF-I was lower in vegan women than in the other groups. The researchers believe that the vegans' lower intake of animal protein or of essential amino acids may explain their lower levels of IGF-I.

Allen NE, Appleby PN, Davey GK, et al. 2002. The association of diet with serum insulin-like growth factor I and its main binding protein in 292 women meat-eaters, vegetarians, and vegans. Cancer Epidemiol Biomarkers Prev. 11:1441-8.