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Why doesn't fasting lead to weight loss?

Dr. Mehmet Oz, MD
Cardiologist (Heart Specialist)
Fasting can lead to weight loss, but the pounds you shed by going without food will likely return once you start eating again. In a 2010 study, researchers at Cornell University asked a group of women to fast for one day, which caused them to lose weight. They were then allowed to eat as much as they liked. The women didn't stuff themselves after going without food; they simply went back to eating what they normally would. Within four days the women's weight returned to pre-fasting levels. The researchers speculate that fasting causes the body's metabolic rate to slow down. That means you burn fewer calories, so returning to a normal diet after fasting will cause any weight you lost to return. Studies suggest that the better way to lose weight is by eating a balanced, low-calorie diet and joining a group such as Weight Watchers.

When our ancestors couldn't find food and went for long periods of time without it, their bodies acted like a life preserver. Their bodies stored fat in anticipation of the inevitable periods of famine. The same system works today. When you try to "diet" by going for long periods of time without eating or by eating way too few calories, your brain senses the starvation and sends an SOS signal through your body to store fat because famine is on its way.

That's why people who go on extreme fasts and extremely low-calorie diets don't lose the expected weight. They store fat as a natural protective mechanism. To lose weight, you have to keep your body from switching into starvation mode. The only way to do it: Eat often, in the form of frequent, healthy meals and snacks.

Start every day knowing when and what you're going to eat. That way, you'll avert the 180-degree shift between starving and gorging that occurs when you skip meals. If you feed your body regularly, you'll avoid extreme periods of over- and under-eating that can lead to a gain in weight and inches.

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YOU: On A Diet Revised Edition: The Owner's Manual for Waist Management

For the first time in our history, scientists are uncovering astounding medical evidence about dieting -- and why so many of us struggle with our weight and the size of our waists. Now researchers...

If you do it long enough, it will - look at starving nations for proof. This method of weight loss is NOT recommended.

If you fast for a few days expecting some crazy loss rate, you may or may not see it. Chances are, your body started convincing you a nap sounded really good, let's skip the gym today and watch some extra TV. If you do manage to see some loss, you probably won't hang onto it. When you get to eat again, you probably overeat.

Just stick to 500-750 calories/day less and get out and walk more. Stay on your feet!

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.