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Nutrition Column

Repeated Dieting Negatively Impacts Your Immune Function

Have you ever significantly decreased your caloric intake in an attempt to lose weight? It worked, right? Well, at least for a little while. Chances are you gained most of it back or even added on a few extra pounds. So, why do 95% of diets fail? The key to losing weight is proper nutrition, exercise, and a minimal reduction in caloric intake.

Your metabolism plays a crucial role in maintaining proper weight. The higher your metabolism, the more energy you expend and the harder it is to gain weight. The most important factor in determining overall metabolism is resting metabolic rate the amount of energy expended while at rest. Most of your resting metabolic function is due to the work of the sodium potassium pump. The tissues that have the highest amounts of sodium potassium pumps are muscle fibers and other excitable tissues. If you restrict your calories by more than 250-300, you will not only lose fat but you will lose a significant amount of muscle mass including glycogen and protein stores. Losing muscle mass will decrease the number of sodium-potassium pumps, slow down metabolism and make it harder to lose weight. This explains why it becomes increasingly more difficult for a person to lose weight if they are severely restricting their caloric intake.

One pound of body fat is equivalent to 3500 calories. If you want to lose a pound, you will have to earn a caloric deficit that is equivalent to 3500 calories. The recommendation for healthy weight loss is 1-2 pounds per week or 1% of body weight in pounds if greater than 200 pounds. This is physiologically possible for your body to burn on a continual basis. If you are losing more than 1-2 lbs per week, then you are losing lean body mass along with fat and are decreasing your metabolic rate. So, if you want to lose a pound of fat a week, you should decrease your caloric intake by no more than 250 per day. The additional 250 calorie deficit should be earned from exercise. If you want to lose two pounds per week, you should keep the caloric restriction the same but increase exercise so that you burn 750 calories.

Why does it seem so much harder to lose weight each time you diet? Not only has your metabolism decreased, but your body has undergone a physiological change, which makes it harder to mobilize your fat stores. Instead of restricting calories, you should start eating foods that are healthier and contain less total fat, saturated fat, and trans fat. Gaining and regaining weight may also impact your overall health by decreasing your immune system function. A recent study reported on the Fred Hutchinson Cancer Research Centerweb site showed that women who reported frequent weight loss episodes had significantly lower immune cell function. The goal of any weight loss program should be to follow healthy eating and exercise habits so that you can continue the rest of your life. A programaimed to sustain lean body mass, reduce fat, maintain fitness & function-all the while keeping you healthy.

Written by Ryan Serrano with Eric Sternlicht, Ph.D. Occidental College, Los Angeles, CA.