As a health practitioner dedicated to teaching my clients how to live the longest, heathiest lives possible for them, there are few things that disturb me more deeply than the current trend of promoting high protein diets (which invariably means animal food-based diets, since virtually no one seems to understand that ALL of our dietary protein is ultimately derived from plants) for weight loss.
Not only have these diets been proven to be complete failures when it comes to maintaining weight loss in the long run (see my article Eating meat: the fast track to diabesity), there’s growing evidence that they increase your risk of developing cancer.
Let’s start by getting familiar with a couple of medical terms, so you can fully grasp the significance of the information I’m about to share.
Insulin-like growth factor 1, or IGF-1, is a hormone that powerfully promotes growth by stimulating cell division. It’s normal to have high levels of IGF-1 during infancy, childhood and our adolescent growth spurt.
But once we’ve reached our full adult height, it’s not normal or healthy to have high levels of IGF-1 circulating in our bodies; in fact, elevated IGF-1 in adulthood drives the growth of cancer. This stands to reason, since one of the defining characteristics of cancer cells is that they divide abnormally rapidly, causing them to accumulate into a tumour.
Our bodies produce IGF binding proteins (IGFBP) to protect us from the cancer-promoting effects of IGF-1. These binding proteins effectively ‘tie up’ the IGF-1 so it can’t send its growth-promoting signal to our cells.
So the ideal environment for the proliferation of cancer cells would be high in IGF-1 and low in IGFBP. Conversely, to reduce your risk of cancer you would want to attain relatively low IGF-1 and high IGFBP.
Multiple studies have shown both that people who already have cancer – particularly breast and prostate cancer – have higher levels of IGF-1 and lower levels of protective IGFBP; and that people who don’t have detectable cancer at the beginning of a study, but go on to develop it during the follow-up period, also have higher IGF-1 and lower IGFBP than people who remain cancer-free (1, 2).
IGF-1 is also crucial to the process of metastasis (the spread of a primary tumour into a vital organ such as the liver, lungs or brain) (3), which is even more frightening, since people usually don’t die from their primary tumour (say, a breast or prostate tumour) but instead from metastases.
So what does this have to do with animal-food based diets? Well, eating meat, poultry, fish, eggs and dairy products raises IGF-1 and lowers IGFBP, largely because of the higher concentration of essential amino acids in animal proteins (the very thing that meat-based diet enthusiasts say is good for us!) (4).
And naturally, the converse is true: just 2 weeks on a plant-based diet significantly lowered IGF-1 and raised IGFBP in overweight, postmenopausal women, while serum (the liquid element of blood) taken from these women inhibited the growth of breast cancer cells significantly more, and caused more of these cancer cells to die, after the 2-week intervention (5). In other words, 2 weeks of plant-based eating increased the cancer-fighting ability of these women’s own bodies.
The same results were found in men: serum from men who undertook a plant-based diet for only 11 days decreased growth and increased apoptosis (‘cell suicide’) in prostate cancer cells, and this was due to reduced levels of IGF-I in the men’s serum after the diet intervention (6).
But what’s even more impressive is the effect of long-term plant-based eating on IGF-1 and IGFBP levels. Men who ate plant-based for 11 days saw their IGF-1 go down by an average of 20%, but men who’d been eating this way for an average of 14 years had 55% lower IGF-1. And while IGFBP-1 increased by 53% after 11 days on a plant-based diet, it was 150% higher in the men who’d been on the diet long-term.
These changes were associated with 30% inhibition of prostate cancer cell growth after 11 days, and 44% inhibition in long-term followers of a plant-based diet (7).
But to reap the full anti-cancer benefits of plant-based eating going vegetarian isn’t sufficent. In a study of 292 British women, only the vegans – not the dairy- and egg-eating vegetarians – had significantly lower cancer-feeding IGF-1 and higher cancer-blocking IGF-BP1 than meat-eating women (4).
The bottom line: The typical weight loss advice given in magazines and gyms not only won’t work to keep you slim, it also raises your risk of developing cancer. But you don’t have to choose between weight loss and health – you can have both! A plant-based diet rich in vegetables, legumes, nuts and seeds, supplemented with fruit and some whole grains, is the most effective intervention for promoting and maintaining weight loss, AND it strongly protects you against cancer.
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