Eating predominantly plants sure has a lot to recommend it these days. Here’s a study that found women who ate a lot of animal food (protein), and a lot of dairy protein, had higher levels of a molecule called insulin-like growth factor-1 or IGF-1 for short. High levels of IGF-1 increase the risk for breast cancer (and other cancers too):
The Association Of Plasma IGF-1 With Dietary, Lifestyle, Anthropometric, And Early Life Factors In Postmenopausal Women, Growth Hormone & IGF Research, April 2015.
OBJECTIVE: Higher circulating concentrations of insulin like growth factor (IGF-I) are associated with an increased risk of breast cancer.
DESIGN: An analysis of plasma IGF-I concentrations (measured by immunoassay) in 1883 postmenopausal women. Multivariate analysis was used to examine correlates of plasma IGF-I concentrations.
RESULTS: Women in the highest quintile of total protein and dairy protein intakes had, respectively, 7.6% and 5.5% higher plasma IGF-I concentrations than women in the lowest quintile (p trend <0.05 for both).
CONCLUSIONS: This study in post-menopausal women identified several potentially modifiable determinants of circulating IGF-I concentrations. There is now strong evidence from this and other studies that IGF-I concentrations are associated with dietary protein intakes.
Maybe this is why a Harvard publication said, “the strongest and most consistent dietary factor linked with prostate cancer was high consumption of milk or dairy products.”