By Michael Greger M.D.
Over the last decade, more than 5,000 papers have been published about TOR, an engine-of-aging enzyme inhibited by the drug rapamycin.
Rapamycin has been used experimentally to extend lifespan, but is already in use clinically to prevent the rejection of kidney transplants. Patients who received rapamycin due to renal transplantation had a peculiar “side effect,” a decrease in cancer incidence. In a set of 15 patients who had biopsy proven Kaposi’s sarcoma (a cancer that often affects the skin), all cutaneous sarcoma lesions disappeared in all patients within three months after starting rapamycin therapy.
TOR functions as a master regulator of cellular growth and proliferation. For example, TOR is upregulated in nearly 100% of advanced human prostate cancers So, reductions in cancerous lesions after rapamycin therapy make sense. TOR may also be why dairy consumption has been found to be a major dietary risk factor for prostate cancer. We used to think it was just the hormones in milk, but maybe prostate cancer initiation and progression is also promoted by cow’s milk stimulation of TOR.
Our understanding of mammalian milk has changed from a simple food to a “species-specific endocrine signaling system,” which activates TOR, promoting cell growth and proliferation and suppressing our body’s internal housecleaning mechanisms. Normally, milk-mediated TOR stimulation is restricted only to infancy where we really need that constant signal to our cells to grow and divide. So from an evolutionary perspective, “the persistent ‘abuse’ of the growth-promoting signaling system of cow’s milk by drinking milk over our entire life span may maintain the most important hallmark of cancer biology, sustained proliferative signaling.”
TOR appears to play a role in breast cancer, too. Higher TOR expression has been noted in breast cancer tumors, associated with more aggressive disease, and lower survival rate among breast cancer patients. Altered TOR expression could explain why women hospitalized for anorexia may end up with only half the risk of breast cancer. Severe caloric restriction in humans may confer protection from invasive breast cancer by suppressing TOR activation.
We don’t have to starve ourselves to suppress TOR; just reducing animal protein intake can attenuate overall TOR activity. Moreover, diets emphasizing plants, especially cruciferous vegetables, have both decreased TOR activation from animal proteins and provide natural plant-derived inhibitors of TOR found in broccoli, green tea, soy, turmeric, and grapes, along with other fruits and vegetables such as onions, strawberries, blueberries, mangoes and the skin of cucumbers.
The downregulation of TOR may be one reason why plant-based in general are associated with lower risk for many cancers. “Are we finally on the threshold of being able to fundamentally alter human aging and age-related disease?” asks researchers in the journal Nature. Only time will tell, but if the pace and direction of recent progress are any indication, the next 5,000 studies on TOR should prove very interesting indeed.
Michael Greger, M.D., is a physician, New York Times bestselling author of “How not to Die” and internationally recognized professional speaker on public health issues.
Gregor is a militant Internet vegetarian and a favorite of this site's editor.