Why diet doesn't work if your goal is to lose weight and shed those extra kilos for good? As soon as you reduce your calorie intake, the body's natural defenses against starvation kick in, and the metabolic rate drops. The body will react as if it were anticipating a famine, slowing down physiological processes (and thereby, the body's RMR) in order to conserve energy to sustain itself for as long as possible. Those dieters eating fewer than 700 calories a day may experience a 20% drop in their metabolic rate.

Negative Effect of Dieting in Your Metabolism:

• Moderate dieters who only consume 1,200 calories/day will have about 5% decrease in their metabolism. So if she has an RMR (resting metabolic rate) of 1,500, that means she will burn 75 less calories a day.
• A slowdown of metabolism (even just a minor drop of 6 to 12%) can cause fatigue, slower reflexes, lowered blood pressure, dizziness, intolerance to cold, constipation, and dry skin and hair. And a drastic decrease of over 20% can produce a more intense symptoms mentioned above.

Exercise versus Dieting:

Working out, as opposed to dieting, sends the right signals to the metabolism. Instead of signaling a famine and slowing down the metabolism when you diet, metabolism gets more active when you workout. Normal activity-which includes both systematic exercise sessions and everyday movements like talking, typing and walking-is the most flexible component of metabolism. A moderately active woman (who exercises approximately 30 minutes, two to four times per week) can burn 400 to 500 calories a day over and above her RMR.

Positive Effect of Exercise:

• Studies shown that exercisers get an additional caloric burn of up to several hours after a workout. You can burn anywhere from 3% to 10% of the calories you burned during exercise, depending on how intensely you worked out.
• Exercise can also elevate the RMR by 10% for as long as 48 hours afterward, and possibly longer.
• Strength training creates more muscle mass, which in turn raises metabolism. Incorporating weight-training into a workout can theoretically increase the number of calories burned by 100 to 200 a day.
• All else being equal, a person who eats three meals a day and exercises moderately will burn more calories than a person who skips meals and exercises on an empty stomach.

Exercise Alert: You should avoid combining strenuous exercise with strenuous dieting. Although working out is good for raising the metabolic rate; dieting, on the other hand, only depresses it. And the combination of few calories coming in and a lot more going out (via rigorous exercise) is perceived by the body as a huge threat; its starvation-defense system goes into overdrive, causing the metabolic rate to plummet.