High-protein intake not harmful for bodybuilders' bones
A high protein intake boosts the amount of calcium that is eliminated from the body in the urine. So a too-high protein intake increases the risk of osteoporosis, say scientific studies. But is this true for bodybuilders, the people with the highest protein-intake on the planet? Probably not, Korean researchers conclude.
Proteins consist of amino acids, and as their name suggests, these are acidic. And the sulphur containing amino acids found in animal proteins are particularly acidic. When the blood contains high concentrations of amino acids, a mild form of the condition that doctors call metabolic acidosis arises.
When this happens the body tries to normalise the acid levels in the blood by drawing on minerals that are stored in the bones. If you have continuously high levels of amino acids in your blood, your bones may become brittle in the long term. Nutritionists have been warning about this for years.
But is the same true for bodybuilders? Running, weight training and other forms of exercise cause tension in bone tissue. This in turn causes a growth stimulus, as a result of which the tissue stores more minerals. The more exercise you get, the stronger your bones will be. As long as this effect is stronger than the reaction to metabolic acidosis, then bodybuilders shouldn't have to worry about osteoporosis as a result of high protein intake.
Korean researchers at the Kyung Hee University studied 8 competitive bodybuilders aged between 18 and 25 who ate an average of 4.3 g protein per kg bodyweight every day. The calcium levels in their urine were on the high side, on the edge of what doctors would find acceptable, but not alarmingly high. Bear in mind that the bodybuilders also consumed high amounts of calcium through the protein supplements they used. Their blood concentrations of calcium were within the bounds of normality.
The bodybuilders were better off than the researchers had expected on the basis of the literature. They concluded that they didn't think the bodybuilders were likely to develop osteoporosis. "It can be presumed that some factors, such as intensive exercise and other dietary factors, would play a role as buffer against increasing urinary calcium excretion in this subjects", they write.
Potassium intake is also a dietary factor. The bodybuilders' potassium intake was high, probably because they eat large amounts of fruit and vegetables, which are rich in potassium. Much of the potassium found in foods is part of compounds that help to keep blood acidity levels low.
And before we forget: In the table above GFR stands for glomerular filtration rate. This is a measurement of kidney function. This also indicates that the bodybuilders don't seem to be having much trouble with their protein-rich diet.
J Int Soc Sports Nutr. 2011 Jul 4;8:10.
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