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Eat To Grow: Bone Voyage

Does bone-building calcium cruise out of your body when you eat more protein?

Critics of high-protein diets often harp on the dangers of protein in relation to calcium loss, particularly for women, who often avoid foods like dairy products that are rich in calcium. Since women are also more prone to the insidious bone-thinning disease known as osteoporosis as they age, a focus on calcium intake appears to make sense. By the way, it’s not just calcium that’s vital for bone preservation in women. There are many other factors, such as estrogen level and weight-bearing exercise’but that’s another story.

Protein is thought to speed calcium excretion because certain amino acids, which are elemental forms of protein, produce greater levels of acid in the body, and calcium is used to buffer such increased acidity, ultimately being excreted from the body.

The idea that higher protein intake promotes increased calcium excretion was recently explained in several studies. One found that increasing protein intake from 0.7 to two grams per kilogram of bodyweight increased calcium absorption efficiency by 40 percent. The most recent study examined 191 Roman Catholic nuns, ages 48 to 70, over a 20-year period.1 It found that neither protein nor phosphorus intake adversely affected calcium uptake in the nuns.

Phosphorus, which, like calcium, is found largely in bone tissue, may block calcium uptake if taken in excessive amounts. That isn’t difficult to do, since phosphorus is ubiquitous in the diet, occurring in most natural protein foods, as well as processed foods such as cola drinks. Yet the study found that phosphorus didn’t adversely affect calcium absorption. The body likely balances calcium and phosphorus uptake as needed, as it does all other minerals. That means more of the mineral is absorbed when needed, while it may be excreted if the body already has enough. IM

1 Heaney, R.P. (2000). Dietary protein and phosphorus do not affect calcium absorption. American J Clinical Nutrition. 72:758-61.

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