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Bone Density Does Not Necessarily Measure Bone Strength

The greater the force you put on your bones during exercise, the stronger they become. Researchers at the University of Missouri in Columbia showed that recreational runners have denser bones than cyclists (Journal of Metabolism, February 2008). Another study from Université de St-Etienne in France show that youth soccer players have an increase in bone density over three years of playing high level soccer (Joint Bone Spine, January 2008). They failed to show that the soccer players had denser bones than their classmates, yet their intuition told them that heavy forces on bones while playing soccer must strengthen bones, so they stated that "The yearly gain im bone density is greater in soccer players than in controls."

These studies and many others comparing various sports measure bone density, not bone strength. The only way to measure bone strength is to see how much force it takes to break them. Needless to say, nobody is doing these studies in humans. So scientists use bone density, which can be measured, as a substitute for measuring bone strength. Nobody has shown that bone density determines bone strength. For example, birds have bones that are not dense because they need a low weight to fly effectively. Yet their bones are very strong. I think that, in the future, methods will be developed to determine bone strength and they will show that measuring bone density is, at best, a crude measure of whether a person is likely to break his or her bones.

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Dear Dr. Mirkin: Does it matter how fast or slow a person eats?

An interesting study from Japan suggests that eating fast is a risk factor for diabetes. Researchers at Nagoya University Graduate School of Medicine in Aichi studied middle-aged men and women and found that the faster a person ate, the more likely he or she was to be fat (Preventive Medicine, February 2008). Furthermore, both insulin levels and blood sugar levels were higher in people who ate faster. High insulin and blood sugar levels are markers for being diabetic or at risk for developing type II diabetes.

Before insulin can do its job of driving sugar into cells, it must first attach to special hooks on the surface of cells called insulin receptors. As a person gains weight, excess fat blocks insulin receptors so they cannot drive sugar into cells. Blood sugar levels rise and the pancreas responds by putting out large amounts of insulin. Insulin makes you ever fatter by acting on your brain to make you hungry and it acts on the liver to make even more fat and on the fat cells in your belly to pick up and store that extra fat. Early diabetes is characterized first by high insulin levels, then by storing fat in the belly, rather than the hips. Eventually the pancreas exhausts itself and stops making insulin completely, and person then must take insulin.

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Dear Dr. Mirkin: What can I do about the fatigue I feel after exercising?

After you exercise intensely or for a long time, you feel exhausted and cannot exercise again comfortably until you have allowed enough time to recover. Part of the fatigue that you feel in your muscles is due to loss of sugar and fat stored inside the muscles, and part is due to damage to the muscle fibers. Many studies show that you will recover faster if you take drinks or foods after exercise, but nobody is certain whether recovery is hastened more by calories, protein or carbohydrates.

Researchers at the University of Bath in England recently confirmed previous studies showing that taking a source of both carbohydrates and proteins helps athletes recover faster for a second bout of competition (Journal of Sports Sciences, November 2007). However, they also showed that putting more nutrients into the drinks (increasing the calories) did more to hasten recovery. It did not make any difference whether the extra calories came from carbohydrates or proteins.

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June 25th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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