Adults require about 0.8 or 0.9 grams of protein per healthy kilogram of bodyweight per day. Does it matter if that protein is from animals or plants? Apparently yes.

The adverse effects associated with long-term, high protein-high meat diets may include disorders of bone and calcium balance, increased cancer risk, disorders of the liver, and worsening of coronary artery disease.

What about our kidneys? Harvard University researchers followed thousands of healthy women for more than a decade to look for the presence of excess protein in their urine, a sign that kidneys may be starting to fail. The researchers found three dietary components associated with this sign of declining kidney function: animal protein, animal fat, and cholesterol. Each is found in only one place: animal products. No association was found between kidney function decline and intake of plant protein or fat.

High animal protein intake may induce hyperfiltration, a dramatic increase in the kidney’s workload. Within hours of consuming meat, whether beef, chicken, or fish, our kidneys may rev up into hyperfiltration mode, whereas an equivalent amount of plant protein causes virtually no such stress on the kidneys.

Animal protein consumption also appears to trigger the release of insulin-like growth factor 1 (IGF-1), a cancer-promoting growth hormone. IGF-1 levels rise during childhood to power our development and diminish when we reach adulthood. Should the levels remain too high, however, our cells will constantly receive a message to grow, divide, and keep going and growing. Not surprisingly then, the more IGF-1 in our bloodstream, the higher our risk for developing some cancers. Animal protein appears to stimulate IGF-1 production whether it’s the muscle proteins in meat, the egg-white protein in eggs, or the milk proteins in dairy. After just 11 days of cutting back on animal protein, however, our IGF-1 levels may drop by 20 percent.

Watching our animal-to-plant protein ratio may be useful for cancer prevention. The largest diet and bladder cancer study found that a 3 percent increase in animal protein consumption was associated with a 15 percent increased risk of bladder cancer, while a 2 percent increase in plant protein intake was associated with a 23 percent decreased cancer risk.

Dr. Ornish and colleagues were able to demonstrate that a nearly exclusively plant-based diet allowed for an apparent reversal in early stage cancer growth, so the ideal animal-to-plant protein ratio may be quite low.

For substantiation of any statements of fact from the peer-reviewed medical literature, please see the associated videos below.

Image Credit: egal / Thinkstock. This image has been modified.

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