(continued from a previous entry, The excesses of modern life and kidney stones)
3. Protein
The New York Times article “A Rise in Kidney Stones Is Seen in U.S. Children” implicates recent high-protein fad diets as contributing to the increased incidence of kidney stones.
Specialists of kidney stones and calcium metabolism have long derided the high level of protein in the typical Western diet as contributing to not only kidney stones but likely also to osteoporosis. (Osteoporosis is more prevalent in Western societies - including in immigrants to the West relative to the inhabitants of their native-born lands – suggesting environmental causes.)
Protein as an acid
In the same way that the body functions best with a certain amount of water, at a certain temperature, etc., the body functions best at a certain acid-base level, a certain pH (7.4). As a result the body works hard to maintain this optimal acid-base state.
Proteins, however, are acidic. They are made of amino acids, and therefore eating protein requires the body to buffer these amino acids to maintain the proper pH - a task which it does using buffers in the blood.
The effects of high protein diets
Eating high amounts of protein, however, overwhelms these buffers in the blood, and the body is forced to find other ways to buffer the extra acid. One of the ways it does so is to break down bone. As expected when bone is broken down, calcium is also released, and extra calcium inevitably spills into the urine.
The kidneys, in attempts to rid the body of the extra acid, acidify the urine, but this makes the aggregation of crystals in the urine easier and further predisposes a person to kidney stones. In addition, the extra acid in the body (this metabolic acidosis) lowers the levels of urinary citrate, a molecule that normally attempts to inhibit kidney stone formation.
Bottom line
With high protein diets the resultant acidic urine, low levels of urinary citrate, and extra calcium in the urine all contribute to the increased risk of kidney stones.
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2 comments:
hmm...but what about the idea that the body was designed to process protein over fat and other molecules? (e.g., we can form glucose from protein and not fat) Who cares if we get osteoporosis if we've already reproduced? Besides, if we're running around in the desert hunting and standing in the sun all day the likelihood of getting OP is slim... but that's really for argument's sake...
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