Sunday, January 23, 2011

Growth hormone and fat loss


Some recent studies have suggested that the increase in some anabolic hormones through exercise, such as testosterone and growth hormone, is irrelevant for muscle growth purposes.Why this is so would require an entire article to be explained. But based on such assertions, it would be a rush to judgment to assume that an increase in such hormones through exercise is worthless. One example of this is a recent study that examined the effects of exercise on reductions in visceral body fat levels.
    Visceral body fat is fat located in the deep abdominal area. This particular fat store is considered especially dangerous because of its close association with the onset of cardiovascular disease, insulin resistance, and diabetes. One reason this is so is because visceral fat is constantly being released into the blood, where it travels to liver. Once in the liver, this fat acts as a substrate for the formation of cholesterol, while also contributing to the development of fatty liver.
    The new study involved 10 men and 9 women, all of whom were obese and had type-2 diabetes. Several of them were taking medication to treat diabetes and high blood pressure. They were randomly assigned to either an exercise group or a non-exercise group. Those in the exercise group did two 30-minute sessions of treadmill walking everyday in the morning and evening for a month. They used an intensity level equal to anaerobic threshold.This means that they exercised using a higher level of intensity, with the anaerobic threshold corresponding to the onset of production of higher levels of lactic acid in the working muscles. According to most exercise physiology textbooks, this is the point where fat oxidation decreases and the body relies more on glucose and glycogen to power exercise. In addition, such textbooks often point out that growth hormone (GH) release during exercise in the obese is blunted to the point of being nearly nonexistent.
     Despite these notable "facts," the subjects who did the exercise for a month showed a 21.7% drop in visceral body fat stores, while those who didn't exercise showed a 5.5% drop, likely because both groups also consumed a diet not exceeding 25 calories per kilogram of bodyweight. Levels of insulinlike growth factor-1 (IGF-1) increased in the exercise group by 5.8%, and 0.5% in the non-exercise group. IGF-1 is a measure of growth hormone release, thus indicating that those who exercised did indeed produce higher levels of GH.
     Textbooks say that to reduce fat requires a high output of catecholamines, such as epinephrine and norepinephrine as a result of exercise. Yet the level of intensity used in this study wasn't enough to boost levels of catecholamines. This shows that the reduction in visceral fat mass in the exercising subjects resulted from an increase in GH levels. Subcutaneous fat stores, or fat stores under the skin, weren't affected. Still, the most dangerous fat stores to health--visceral fat stores--were significantly decreased in only a month. This led to beneficial changes in several health indicators, such as increased insulin sensitivity, and better glucose and fatty acid metabolism. Note that the subjects were all type-2 diabetics who have significant defects in glucose and fat metabolism. One wonders what such exercise would do for a person who isn't diabetic. At the least, it would help prevent the onset of diabetes, cardiovascular disease, and even cancer by lowering visceral fat stores.
     Based on the findings of this study, it appears that an increase in GH produced by exercise does indeed offer significant health benefits. In addition, it's clear that GH does promote lower fat stores, at least in the visceral fat stores,even in those with excess bodyfat. We can translate this into explaining the phenomenon of the metabolically fit, yet fat people who regularly exercise, but show no signs of impending disease.

Yamaguchia T, et al.Effect of exercise performed at anaerobic threshold on serum growth hormone and body fat distribution in obese patients with type-2 diabetes.Obes Res Clin Pract 2011;5:e9-e16.