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What causes reduced metabolism in a person who is a chronic dieter?

The simple answer to this is that over a period of years the yo-yo effect of going on and off of diets is a slow stripping of lean body mass. Also, if these diets border on starvation levels your body simply reduces your burn rate to compensate for such huge reductions in calorie intake. Your lean mass or muscle has a metabolic need of roughly 25-50 calories per pound per day. If you, over time reduce your lean body mass and burn rate through starvation type diet principals you simply set yourself up for higher and higher percentages of overall body fat even at lower and lower levels of body weight and very real reductions in caloric need. This effectively reduces your total metabolic rate significantly over time.

We all have to learn to reduce calories systematically while maintaining a smart fitness program that helps us retain muscle while we lose body fat. This is how we maintain our metabolic rate while reducing body fat and overall body weight.

Kent Holtorf, MD
Endocrinology Diabetes & Metabolism
There are a number of physiologic mechanisms that result in a hypo-metabolic state seen with overweight and chronically dieting individuals. The thyroid hormone called T3 has long been known to be the body's metabolic gas pedal. This hormone is shown to be a major culprit in the drop in metabolism seen with dieting and weight gain, as acute or chronic dieting can result in a significant decrease in intracellular and circulating T3 levels by up to 50 percent, which significantly reduces basal metabolic rate (the number of calories burned per day). Studies show that with chronic dieting, the thyroid levels and metabolism often do not return to normal levels; the body stays in starvation mode for years with significantly reduced metabolism despite the resumption of normal food intake, making it very difficult to lose or maintain lost weight.

For instance, one such study published in American Journal of Physiology, Endocrinology and Metabolism found that 25 days of calorie restriction (dieting) significantly reduced T3 production by 50 percent. Many other studies have found similar reductions in T3 levels with dieting and in those with insulin resistance and diabetes. The problem is that these studies also show that the common test used by endocrinologists and other physicians, called the thyroid-stimulating hormone (TSH) test, fails to detect these dramatic drops in thyroid activity. Thus, all these patients are erroneously told that they have a "normal" thyroid levels.

Another potentially treatable cause of the reduced metabolic rate in a large percentage of overweight individuals is shown to be a leptin resistance. The metabolic effects of leptin resistance include a diminished metabolic rate, reduced production of the active thyroid hormone, T3, and an inhibition of lipolysis (fat breakdown).

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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.