Saturday, April 6, 2013

Fitness III: Lean mass and metabolism

"Myths, Presumptions and Facts about Obesity" appeared a January 2013 issue of the New England Journal of medicine. Among the presumptions, which means ideas that are widely circulated but have not been confirmed or denied by academic research, is that "weigth cycling is associated with increased mortality". Weight cycling, aka yo yo dieting, refers to repeated weight loss and regain. When we lose weight, we are trying to lose fat but as I learned in analyzing my own numbers, we also lose quite a bit of lean mass. If my own figures are accurate(based on caliper measurement of bodyfat %) 20-30% of my weight loss was lean mass while I was exercising daily. I shudder to think what happened when I was just dieting. It's probable that of 46 pounds I lost in 2012, as much as 15 were lean mass. Let's hope some of that was skin. There are a couple of ways the amount of calories you burn in a day can be calculated. The Harris Benedict equation takes your height and age into account along with your age. It assumes your metabolism and lean mass decrease as you age. Whereas the Katch McArdle equation goes simply off lean body mass (which is 100% minus bodyfat%) What all this means is that part of the reason exercise is so important to weight maintenance is because you have probably lost a lot of your lean mass as you attained your goal weight. Getting back to the presumption about yo yo dieting, there is a sense that weight loss somehow damages the metabolism. This was addressed in an NWCR study that found the decreased caloric needs of maintainers were consistent with known the known factors of calorie equations such as age and lean mass. (Wyatt et al. 1999) While only 20% of NWCR maintainers lifted weights, it was the third most prevalent exercise used (Thomas and Wing 2009). My experience was that when I began eating a maintenance diet, my strength training became much more effective, whereas while I was losing weight progress in my strength program was miniscule. So the action step for this segment is to think about the role of building lean mass in your fitness program. Do you do strength training either weights or other kinds of resistance training? Have you tried increasing intensity since reaching goal, and what have you found? Resources: Wyatt et al. 1999, Reduced Energy Expenditure in reduced-obese subjects in the National Weight Control Registry A blog post by a bariatric doctor that discusses the points of Myths, presumptions and facts about obesity (the full article is not available to the public).

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