Fit Or Fat: Nutrition and Exercise

Does Dieting Slow Down Metabolism?

Posting Date: 06/26/2000

Q: I've started a new diet that reduces my calories and limits some foods. I am wondering if this will mess up my ability to burn fat?

A: A lot of metabolism takes place in the body after exercise. Most people think they've stopped using calories, but they haven't. All of these metabolic processes work madly to accomplish just one goal -- to replace muscle glycogen.

Think of all the metabolic processes that work hard to replace glycogen after exercise. The liver snatches carbohydrates from your last meal, makes them into glucose, and packs them off to the muscles. The liver also converts amino acids (the building blocks of protein) into glucose.

The pancreas works hard after exercise to release the hormone insulin so that sugar can enter the muscles. Then there is the obvious demand for energy when sugar is made into glycogen in the muscle itself. Finally, fatty acids are burned in the muscle to produce the energy to synthesize glycogen.

Where do fatty acids come from within your body? They come from fat cells, don't they? Fat cells throughout the body are releasing -- metabolizing -- fatty acids, and that process requires energy. In the muscle, energy is needed to burn the fat molecules in order to make energy to make the glycogen. Talk about complex!

Even lactic acid gets into the act. The liver says, "Oh, brother! Here's some lactic acid. What am I supposed to do with it?" The liver puts the lactic acid through chemical changes, makes it into sugar, and sends it back to the muscle, where it can be made into glycogen. (Read more about lactic acid and what it is in my article, Should I 'Go For The Burn'?)

I?ve used this long-winded explanation to tell you just what happens in the body as a result of exercise. All of these processes that take place in your body help speed up your body's metabolism, or increase your ability to burn more fat. They have such an enormous impact, imagine the effect exercise has on all the other demands of the body!

Dieting, or restricting the calories you consume, has just the opposite effect. Overweight people sign up for expensive diet programs because their metabolism is slow. Even responsible physicians prescribe diet programs that only treat fat people's symptoms, doing nothing to "fix" their metabolism.

The most popular diet programs are the ones that make people lose weight fast, which depresses their metabolism even further. Instead of helping people speed up their slow metabolism, these programs make the problem worse. None of the weight loss diets increase even one of the glycogen-building processes. Exercise enhances all of them.

Adapted from Smart Exercise: Burning Fat, Getting Fit by Covert Bailey. Copyright 1994 by the Covert Bailey Revocable Trust, published by Houghton Mifflin Company. All rights reserved.

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