By Dr. Jeremy Girmann
A few questions related to dietary protein intake recently appeared in my inbox accompanied by links to some rather bewildering blogs. The objective of the blog postings seemed to be the perpetuation of what have become rather tenacious myths about high protein diets. Among the problems said to be associated with high protein diets are loss of calcium, fat accumulation, and kidney dysfunction. I think that it’s worth spending some time to examine each of these.
Some sources have cited a concern related to the possibility of high protein diets contributing to osteoporosis due to increased excretion of calcium. It has in fact been shown that when dietary protein is increased, urinary calcium excretion also increases. This observation led to the following theory: protein increases the acid load of the body and in an attempt to decrease this load, calcium is “leached” from the bones in order to serve as a buffering agent. The body does seek to maintain blood pH within a very narrow range, and while it is true that calcium is a natural buffering substance, there are several other more readily available substances that the body can use to balance any increase in acid load. In addition, the supposition that increased calcium excretion must mean loss of calcium from the bones is simply incorrect. In fact, it has been demonstrated using stable isotope studies that a higher protein diet results in greater intestinal absorption of calcium therefore leading to a “more in, more out” phenomenon. Further, it has actually been shown that LOW protein diets can reduce intestinal calcium absorption to the point where parathyroid hormone (a hormone responsible for releasing calcium from bones) can become elevated. Pounding a final nail in the coffin of calcium concerns, several long-term studies have shown improved bone health with high protein diets, which is likely related to the function of hormones such as insulin like growth factor-1 (IGF-1).
Next let’s consider the suggestion that a high protein diet will make you fat. Before diving into this one, it’s important to maintain conversational context by recognizing that active individuals, and particularly people who regularly engage in weight training, will have a higher protein requirement due to greater protein turnover and the need for additional amino acids to fortify muscle tissue. As a result, a large portion of the ingested protein in these individuals will never be fated for fat tissue merely because it is being used to build muscle. What, however, becomes of the protein that remains? The broad stroke belief that “a calorie is a calorie” would lead one to assume that an excess of protein would convert to fat in the same way that carbohydrates or fat might. This assumption, however, is fundamentally flawed. The body’s metabolic processes are brilliantly complex and while it is possible for portions of amino acids to undergo eventual conversion to fat molecules, this route is rather circuitous and energetically inefficient. The digestion, absorption, transport, metabolism and storage of protein constituents require significantly more energy than for carbohydrates or fats. The net effect is that more of the energy provided by protein is burned and less is available to be stored around our waistlines. While the biochemistry does make for some pretty compelling late night page-turning, perhaps more meaningful is the fact that dozens of studies have now shown that higher protein diets are associated with more favorable body composition in actual people…
From observational studies to tightly controlled trials, diets higher in protein by and large reveal leaner physiques.
Some other proteinaceous points to ponder: By increasing certain hormones such as glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GIP-1), and cholecystokinin (CCK), protein has a satiating effect, which can decrease the total amount of food that people eat. Also, a higher protein diet usually results in more total muscle mass and since muscle is a very metabolically active tissue, more calories are likely to be burned.
Finally, if you’re putting more protein on your plate, you’re probably putting less of something else. In other words, consideration of what you don’t eat is just as important as the things that you do. If a few extra ounces of fish replace an extra serving of pasta, there is likely to be a reduced propensity for fat accumulation.
The last myth to be busted in this article is one that I hear most commonly – “Extra protein will trash the kidneys.” (Sigh…this myth just won’t die.) Perhaps starting in on this one with a most direct approach is best: There is zero evidence that a high protein diet will negatively affect healthy kidneys. Whether they know it or not, many of the people who perpetuate this protein preposterousness (I’m on a role with alliterations today) are extrapolating from what was initially known as the Brenner hypothesis. In the 1980’s, a paper by Dr. Barry Brenner appeared in the New England Journal of Medicine, which described the relationship between dietary protein intake and progressive kidney disease, noting that increased protein load can accelerate kidney dysfunction in cases of pre-existing kidney disease. Microscopic units in the kidneys called glomeruli act as tiny filters, cleansing the blood and ridding the body of waste products. Higher protein intake leads to an increase in glomerular filtration rate (GFR) to which the body well adapts under normal circumstances, as has been confirmed in multiple studies. When the filters are damaged as in pre-existing kidney disease, however, the damaged filters do not properly adapt. The World Health Organization has even emphasized this distinction between healthy and diseased kidneys:
“In a group of subjects covering a wide range of dietary protein intakes, the glomerular filtration rate was related to the protein intake…chronic protein intake is a determinant of glomerular filtration rate, but does not suggest a role for protein intake in the deterioration of kidney function.
…the most widely quoted potential problems related to renal function and damage, but as discussed above the evidence for such claims in otherwise healthy individuals does not stand up to scrutiny.”
I suspect that any anecdotal reports of kidney dysfunction associated with high protein diets represent misdirected blame – cases where high blood pressure, often unrecognized, is the actual source of the problem.
So…if you’re an otherwise healthy individual who eats a balanced diet and prefers to consume a higher amount of protein, should you be concerned? No whey, I say!