Traditional Dieting Slows Metabolism Despite Exercise

Spin class

(HealthCastle.com) In a recent article in The Journal of Clinical Endocrinology & Metabolism, a group of obese individuals took part in a traditional weight loss model consisting of caloric restriction & exercise to see if both muscle mass and metabolic rate could be maintained.

Can exercise prevent dieting-induced reductions in metabolism?

The story

After 7.5 months, more than one-third of the participants' initial weight was lost; 17 +/- 8% of that was fat-free mass or muscle, and 83 +/- 8% as fat. Resting metabolic rate [the amount of calories burned to maintain essential bodily functions] "declined out of proportion to the decrease is body weight" demonstrating a dramatic metabolic adaptation of -244 +/- 231 calories/day at week 6 and -504 +/- 171 calories/day by the end of the study more than what was predicted. In other words, the participants' metabolism slowed, they were burning less energy just to keep the essentials going like breathing - and exercise could not compensate for it....insert sad face emoticon now!

The lesson

Cutting calories [food energy or dieting] and increasing calories burned [energy used] puts the body in an energy deficit - a.k.a. starvation mode. What does the body do to defend itself against starvation? It slows down the metabolic rate and conserves energy by using less AND it becomes super efficient at using whatever food energy it does get meaning fat loss becomes more difficult; fat storing enzymes, as well, are on high alert and are hard at work.

The kicker of course is that the original body weight set-point is still higher [the higher body weight before the diet/exercise program started], the body 'thinks' it's still obese, and as soon as anyone in this situation starts to eat more calories, to try and maintain this new weight, will quickly find him/herself putting on a ton of new fat, thanks to those pesky fat storing enzymes that are working overtime.

To make matters worse, as this study points out, any weight loss plan that leads to a negative energy balance works against us by stimulating muscle loss. Why? Because our bodies are still looking for energy, if there's not enough from food, the easiest place to get it from is muscle. It is a lot easier to break muscle protein down, and turn it into glucose, than it is to break down fat. Fat will still be lost but so too will the precious muscle we want to maintain, and again, once someone goes back to eating normally, the body shuttles the food calories to the fat cells, or energy bank account, as the priority

To keep the weight off, using this model, a person would have to engage in an inordinate amount of activity and continue to restrict food...not very likely...case in point is what happens to the participants of The Biggest Loser, upon leaving the show with a broken metabolisms, participants gain back the lost fat.

The study's author's own conclusion sum it up well...

"Unfortunately, fat free mass preservation did not prevent the slowing of metabolic rate during active weight loss, which may predispose to weight regain unless the participants maintain high levels of physical activity or significant caloric restriction"

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