A study published in the British Journal of Cancer compared IGF-1 levels in vegans, vegetarians and meat-eaters¹. Insulin-like growth factor-1, known as IGF-1, is a hormone that is necessary for proper growth in children, but is now understood to be a major contributor to the growth of tumors in both men and women over the age of 40.
The study recruited 696 men: 226 meat-eaters, 237 vegetarians and 233 vegans. In addition to comparing IGF-1 levels, the researchers also looked at the differences in testosterone levels between the three groups.
After adjusting for important variables, such as age, smoking status, and even vigorous exercise, the vegan participants of the study had, on average, 16% more testosterone than the meat-eaters, and 10% more than the vegetarian group. After adjusting for body mass index as well as SHBG (sex hormone binding globulin), the carnivore and vegetarian groups had very similar levels of testosterone, while the vegan group maintained higher levels.
Even more revealing was the fact that vegan men had a significant 9% lower IGF-1 concentration compared to meat-eaters, and 8% lower compared to vegetarians. It is believed that an 8-9% difference is large enough to significantly reduce the risk for prostate cancer. An earlier study found that men that develop prostate cancer have IGF-1 levels that are just 8% higher than men who remain healthy².
The researchers concluded the following:
“The results did not support the hypothesis that meat-eaters have higher levels of bioavailable androgens [testosterone] than non meat-eaters. No differences in hormone levels were found between meat-eaters and lacto-ovo-vegetarians, suggesting that vegetarian diets may not alter prostate cancer risk, but the relatively low IGF-I levels in vegans might reduce their risk of prostate cancer.”
The results of this study are consistent with decades of scientific research that show us why individuals on a proper plant-based diet have significantly lower rates of cancer than both meat-eaters and vegetarians. Furthermore, an increasing number of elite athletes as well body builders are switching to a plant-based diet to gain competitive advantage. Slowly but surely, we are breaking away from strongly held misconceptions that meat consumption equates to more muscle and better performance.
Want to be more manly?
The common stereotype we have in North America of a “manly man” depicts a testosterone-fueled meat-eating machine with a high sex drive. But in reality meat-eaters have lower testosterone than their vegan counterparts and tend to suffer greatly from erectile dysfunction. Add an enlarged prostate to the mix, along with difficulty urinating, and you have a vision of a meat and dairy consumer that more closely resembles the truth.
Perhaps it’s time we put an end to stereotypes, pay attention to the scientific evidence regarding the benefits of a plant-based diet, and get our erections back. We are men, after all.
Nutrition & Exercise Specialist
1. Allen NE, Appleby PN, Davey GK, Key TJ. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Br J Cancer. 2000;83:95–7.
2. Chan JM, Stampfer MJ, Giovannucci E, Gann PH, Wilkinson P, Hennekens CH and Pollak M (1998) Plasma insulin-like growth factor-I and prostate cancer risk: a prospective study. Science 279: 563–566