Friday, January 13, 2012

New experimental evidence suggests why weight loss is not just calories in vs. calories out

Exercise induces the release of a hormone called irisin, which converts white fat into thermogenic (calorie-burning) brown fat, according to a new paper published Wednesday in Nature. They motivate the paper by saying, "Exercise has the capacity to improve metabolic status in obesity and type 2 diabetes, but the mechanisms are poorly understood. Importantly, exercise increases whole body energy expenditure beyond the calories used in the actual work performed." The paper begins to explain how it may be that exercise burns more calories than those in the actual work: that is, much research in the exercise science literature finds that anaerobic exercise (like strength training and high intensity intervals) burns calories for 48 hours afterwards. Perhaps this hormone begins to explain why.

Meanwhile everyone is still despairing slightly because of the NYT Magazine article suggesting that body weight setpoints make permanent weight loss very difficult for almost everyone. The article mostly quoted people who used very low calorie diets that induce starvation conditions and steady-state cardio. As many have noted, steady state cardio doesn't work. People who stay away from processed food and use high-intensity intervals and strength training may have more luck maintaining weight loss.

If I understand the biochemistry, other research already found that high-intensity exercise increases a related protein (e.g., as found in Tabata's paper, famous for his intervals). We already know that anaerobic exercises burn more calories for longer and result in greater fat loss and less muscle loss. This paper suggests why: anaerobic exercise may be most effective in converting white fat into brown fat.

I am disappointed not to see a practical conclusion --- more weight lifting and intervals, less low-calorie dieting --- in the NYT Magazine article. The message is still "just walk more", which clearly doesn't work, but people say it because it seems realistic and attainable (never mind that it's cold outside.) Instead "do something hard" might result in people pushing themselves more and gaining more of the benefits of exercise demonstrated in this paper. I wonder what state the science would have to be in before the messaging on exercise changes.

After reading the paper, I did 3 simple Tabata intervals, and from this paper now I know that the irisin makes it worthwhile.

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