Where Diets Go Wrong (2)
Our bodies are always active. Even when we are asleep, we are breathing, our blood is pumping through our veins, our body temperature is carefully monitored and regulated, and our minds are conjuring up dreams of our worries and desires. The body is expending a fair amount of effort every minute keeping its machinery in running order. When we awaken, the activities of the day demand much more of the body’s energy.
To power all these activities, our bodies can use the energy of foods or the energy stored as fat. We use up these fuels the way an automobile burns gas. A car that is roaring up hills and zigzagging through traffic uses up a fair amount of gas, while a car that is idling or slowly moving along will leave a lot in the tank.
The speed at which our bodies consume energy is called the metabolic rate. In periods of food shortage the body slows down the metabolism to conserve energy. Just as a motorist who is running out of fuel tries to go easy on the accelerator and drive very smoothly to conserve gas, the body does the same sort of thing when food is in short supply. It turns down the metabolic flame to save as much of the fat on your body as possible until the starvation period is over, because fat is the body’s fuel reserve. Body functions are turned down a bit, body temperature may fall, constipation will occur, and menstrual periods may stop.
If you go on a low-calorie diet, your body thinks you are starving. You can explain to your body that you are not trying to save your fat, you are trying to get rid of it. But your body is not listening. The more your food intake drops, the harder your body tries to keep from losing fat. The effect is significant. On a 500-calorie diet, your metabolic rate can drop 15 to 20 percent below normal.