2 amerikanische Forscher behaupten, dass nicht alle Kalorien im Körper gleichermaßen umgesetzt werden. Insbesondere entstehen bei der Verwendung von Kalorien aus Proteinen höhere Wärmeverluste als bei Kohlenhydraten, so dass diese weniger stark ansetzen. Die beiden Forscher bemühen also die Gesetze der Thermodynamik, um zu zeigen, dass nicht alle Kalorien gleich sind. Man könnte es thermodynamisch auch so ausdrücken: Bei einer Low-Carb-Diät wird bei gleichen Kalorien mehr Gewicht verloren (bzw. weniger neues Fett angesetzt), weil es einem dabei wärmer ist.
In a paper published last week in the Nutrition Journal, researchers from SUNY Downstate Medical Center show that low-carbohydrate, high-protein diets can be expected to be more effective for weight loss than low-fat diets. Their supposition goes against long standing prejudices of the nutritional community which for years have claimed that only calories count in the battle to lose weight.
"There are numerous examples of low-carbohydrate diets being more effective than low-fat diets with the same number of calories. It doesn't always happen but it can happen," said Dr. Richard Feinman of the Department of Biochemistry, SUNY. "The nutritional establishment has been reluctant to accept this, because they say it violates the laws of thermodynamics. However, they have not really looked seriously at thermodynamics. If they had, they would see that these results are possible, and according to the second law of thermodynamics, are also to be expected."
Feinman and Fine reviewed the existing literature on studies that compared low-carbohydrate and low-fat nutritional approaches. In doing so, they found a sufficient number of reports in the literature to establish the existence of a metabolic advantage. Clinical studies from such well-established research facilities as Duke and Harvard(1)(2), among others, were reviewed and analyzed. The researchers tabulated results from 10 studies, demonstrating that low-carbohydrate diets can lead to greater weight loss than isocaloric low-fat diets.
To explain this metabolic advantage, Dr. Feinman and Dr. Eugene J. Fine suggest that carbohydrates make an efficient fuel for the body, whereas protein does not.
"Your brain needs glucose to function properly," Feinman said. "There's no argument about that. Now, this glucose can come from dietary carbohydrates, but your body can make glucose from protein and, to a much lesser degree, from fat. However, the process of making glucose from protein is inefficient, and to get the extra energy needed, your body will burn the fat that it has already stored. I think that's the bottom line."
The researchers stress that the human body is not a storage locker. They compare it to a machine, and the efficiency of the machine is controlled by hormones and enzymes, which are impacted by nutrients. Carbohydrates increase insulin and other hormones that regulate enzymes which can lead to storing fat rather than burning fat.
"Of course, people are different" said Dr. Eugene Fine, a professor of nuclear medicine at Downstate and Jacobi Medical Center in the Bronx. "But many people are sensitive to the effects of carbohydrates and for them, a low- carbohydrate diet is going to work well." The practical point is that getting rid of the idea that "a calorie is a calorie" opens the door for serious research into what kind of diets will be most effective and which people will benefit most.
"This is important," Feinman explain "because millions of people are seriously trying to lose weight on low-carbohydrate diets, and instead of being given directions on the best way to do this, they have been largely discouraged by health professionals and self-appointed expert groups. The obesity epidemic is too important to allow this to happen."
- Westman, E.C., Mavropoulos, J., Yancy, W.S., et al., "A Review of Low-Carbohydrate Ketogenic Diets", Current Atherosclerosis Reports, 5(6), 2003, pages 476-483.
- Greene, P., Willett, W., Devecis, J., et al., "Pilot 12-Week Feeding Weight-Loss Comparison: Low-Fat vs Low-Carbohydrate (Ketogenic) Diets," Abstract Presented at The North American Association for the Study of Obesity Annual Meeting 2003, Obesity Research, 11S, 2003, page 95OR.
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