Low-Carb Diets and Bone Health

Mark Anthony, Ph.D., joins the Wellness Foods family as a contributing editor with the monthly column, "Nutrition Beyond the Trends." This month: the relationship between protein consumption and bone health.

By Mark Anthony, Ph.D.

Many nutritionists criticize high-protein/low-carb diets as both nutritionally unbalanced and unhealthy for bones. But a new study suggests a more interesting picture. A high-protein/low-carb diet could make bones stronger by helping them hang onto calcium. Ironically such a diet could also help your body hang on to fat.

The relationship between dietary protein and bone health is highly complex. It’s also controversial, often pitting meat-eater against vegetarian and low-fat dieters against low-carb proponents. Before adding fuel to the fire, here’s some background.

Because many studies have reported increasing levels of urinary calcium with increasing protein consumption, it’s been surmised a high protein diet draws calcium out of the bones. The connection goes something like this. Eating more protein, especially meat protein, increases the acid load of the blood — a result of digesting the sulfur-containing amino acids in protein. To neutralize this acid load, bones give up some of their calcium store to act as a buffer, keeping the blood acid balanced. The integrity of the bone is compromised as the calcium is lost in urine.

This picture may be too simple. Recent studies reveal the higher urinary calcium actually comes from enhanced absorption of dietary calcium due to the higher protein intake.

Moreover, translating bouncing protein and calcium into the practical reality of bone mineral density (and protection from fractures) has also yielded conflicting results. While higher meat consumption is associated with higher bone mineral density, higher vegetable protein consumption is associated with lower hip fracture rate. The general consensus is that more and longer studies need to be conducted.

A Tufts University study published in the Journal of Clinical Endocrinology (March 2004) found certain biomarkers of bone health improved when meat protein was substituted for carbohydrates in the diet. Healthy older men and women were selected for this study based on previous diet. Those with a natural low-protein diet (defined as 0.8 mg/kg body weight) were chosen. Dietary records were obtained from study participants who received diet management instructions to cover the two months of the study. Participants were divided into two groups according to the supplements they took: meat or carbohydrate (rice or pasta with oil).

The high-protein group experienced a significant reduction of bone resorption, increase in total body bone mineral calcium and insulin-like growth factor (IGF-1) when compared to the low protein group. The conclusion: Short-term high-protein diets do not harm bones; they might even improve them. That’s great news for all the low-carb dieters. Bring on the jerky! (Caveat: The authors did caution against over-interpreting the results.)

But wait a minute. There’s an interesting sidebar to the study. Both groups ate a similar diet going into the study, and neither group experienced a weight change during the study. While the high-protein group maintained more of their lean mass than the low-protein group, the low-protein group consumed nearly 400 more calories than the high-protein group, and both groups increased significantly in body fat.

It seems the high-protein group averaged 1,462 calories (43 percent protein, 32 percent fat, 24 percent carbohydrates) and gained body fat! Moreover, one of the biomarkers of bone health was the increase in blood levels of IGF-1.

This also brings to mind studies on the effects of lycopene (the red antioxidant pigment of tomatoes) and bright red fruits such as watermelon, pink grapefruit and blood oranges. Tomatoes (and lycopene) lower risk of prostrate cancer. One of the speculated reasons is the reduction of the very same IGF-1 needed by proliferating cancer cells.

Protein is good stuff, that’s why it’s called protein “of first importance.” The fact that calcium is lost in urine with increased protein intake does not necessarily spell osteoporosis. That you can eat a diet adequate in all respects with no unreasonable fear of meat, and maintain or improve bone health is good news.

So what’s the take-home message? While the short-term high-protein/low-carb diet probably won’t hurt your bones, its very raison d’être appears to dissipate. And since it only takes moderate protein consumption to improve biomarkers of bone health, extreme diets aren’t necessary. They never were. Something far more exciting — a naturally balanced diet — is the most effective for health.

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