Sunday, April 17, 2011

EAT TO GROW Atkins for Exercisers? by Jerry Brainum

Is the low-carb plan suitable for those who work out?

The Atkins diet, which was developed by the late Dr. Robert Atkins, is an ultralow-carbohydrate diet that initially permits an intake of less than 1 percent carbohydrate. The concept behind it and other low-carb diets is that most people who have excessive bodyfat levels produce too much insulin because all of that bodyfat has made them insulin insensitive. To compensate, the body oversecretes insulin in response to meals, especially those containing a lot of carbohydrates. Excess insulin not only perpetuates obesity but also blunts other mechanisms that promote the use of fat as fuel.

Atkins believed that by limiting carb intake, you lowered insulin output and would begin to burn excess bodyfat. Critics of Atkins often lambasted that concept, noting that without excess calories insulin itself couldn’t make you fat. They also voiced alarm over the diet’s high-fat aspects, suggesting that it was a sure route to cardiovascular problems. Recent research has confirmed many of Atkins’ ideas. Compared to other diets, low-carb diets prove superior in promoting initial weight loss. Although some of that loss is water from glycogen breakdown (glycogen is stored with three grams of water per gram of glycogen), low-carb diets promote greater bodyfat losses, an effect traced to their higher relative protein content. Eating lots of protein imparts greater satiety, which eventually leads to an automatic reduction of total caloric intake. Low-carb diets are also superior in promoting an enhanced thermogenic effect, leading to a greater oxidation of fat.

Reports of increased cardiovascular disease due to a higher fat intake with the Atkins diet have also proved false. Indeed, a surprising aspect of the regimen is a clear beneficial effect on several protective cardiovascular risk factors, such as increased high-density lipoprotein and lowered blood triglycerides.

The one aspect of the Atkins diet that hasn’t changed since its inception in the 1970s is its effect on exercise. In his initial writing on the diet, Atkins explained that his diet plan might not be suitable for those engaged in intense exercise, which relies on a sufficient store of glycogen in muscle. The primary nutrient that replenishes depleted glycogen stores is carbohydrate, and Atkins recognized that. A recent study confirmed the point.1

Nine people followed the Atkins diet for a week. Their exercise time was reduced by 56 percent, and their blood glucose levels went down, but they all also showed a loss of bodyweight and bodyfat. One notable flaw of the study was its short duration. It takes a few weeks for the body to adjust from a sugar-burning to a fat-burning machine. In addition, Atkins himself modified the diet over the years, calling for a greater intake of low-glycemic-index carbs, such as fruits and vegetables. That adjustment would likely permit the beneficial fat-loss effects of the diet while also supplying carbs to replenish glycogen.

1 Forbes-Lorman, R., et al. (2005). The Atkins diet decreases exercise capacity. Int Soc Sports Nutr. 2:10.

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