Progress in Science?
Barbara A. Brehm
Readers who were fitness professionals in the 1980s probably learned that weight control was a simple matter of thermodynamics. People consume energy in food. They use calories through resting metabolism, digestion and physical activity. One pound of body fat is worth about 3,500 calories. Create a 3,500-calorie deficit by decreasing energy intake and increasing energy expenditure, and 1 pound of fat should be lost. Simple, right?
Well, not exactly. While the laws of thermodynamics still apply to energy balance in humans, we have learned more over the past 20 years about the many factors that affect energy balance. Here are some of the most interesting scientific findings that have come to light since publication of Fitness Management's first issue in 1985.
The importance of genetics
For centuries, scientists have observed enormous individual variation in body types and body composition, and in the factors that contribute to energy balance. During the past two decades, studies of twins have led to the conclusion that genetic variation explains only about 25 percent of the variation among people in body composition. While this percentage is fairly important, this conclusion also means that 75 percent of the variation we see in body composition is caused by other factors, such as eating and exercise behavior.
Nevertheless, for some individuals and ethnic groups, genetic predisposition for obesity is extremely strong. Their "thrifty" genes allow them to capture every calorie they consume, and to efficiently store energy, primarily as fat. Unfortunately, in an environment where food is plentiful, these thrifty genes translate almost automatically into obesity.
The biochemistry of obesity
Over the past two decades, researchers have learned that adipose tissue is more than a holding tank for extra calories. This active tissue sends and receives chemical messages that affect fat storage, appetite and other metabolic activities. For example, when fat cells start to shrink, they release the hormone ghrelin, which increases appetite. Similarly, as fat stores dwindle, they release less leptin. Lower levels of leptin lead to feelings of hunger. While these messengers kept us from starvation in lean times by encouraging us to look for food, in today's environment, they complicate our efforts to eat less and reduce body fat.
Another interesting messenger affected by adipose stores is adiponectin. Adiponectin helps insulin do its job of getting sugar from the bloodstream into cells, where it can be stored or used for energy. As fat levels rise, their secretion of adiponectin falls, which may help explain the insulin resistance that often develops with obesity.
Health risks of obesity
For 20 years, scientists have engaged in a heated debate about the health risks of obesity. Is it too much fat that causes diabetes, hypertension, heart disease and stroke? Or is it the sedentary lifestyle that tends to accompany obesity? Researchers now believe it is some of each. Overweight people with healthful lifestyles (good eating habits and regular physical activity) have lower health risks than their normal-weight but sedentary friends. However, their risk of obesity-related disorders is still significantly higher than that of their lean and active peers.
Progress in treatment?
Gastric bypass surgery for obesity has received a great deal of press. While surgery has helped some people, the dangers and expense of these procedures make it a treatment option of last resort.
And diets? Success rates of diet programs remain as dismally low as ever. Atkins has come and gone again since its debut in the 1970s. North Americans, and indeed people in developed areas around the world, are fatter than ever. Researchers agree that this rise in obesity is occurring because people have engineered an environment that provides too much of the wrong kind of food, and too little demand for physical activity.
One piece of good news is the growth of the fitness industry. While we must continue to expand the diversity of the clientele we serve, we should be proud of the fact that we provide sanctuaries where people can enjoy physical activity and find support for the healthful lifestyles that help to prevent obesity. The world needs us more than ever!
Black, S.A. Profiting from functional fitness. Fitness Management 21(2): 40-42, February 2005.
Stanton, R., P.R. Reaburn and B. Humphries. The effect of short-term Swiss ball training on core stability and running economy. Journal of Strength and Conditioning Research 18(3): 522-529, August 2004.
Tortora, G.J., and S.R. Grabowski. Principles of Anatomy and Physiology. HarperCollins: New York, N.Y., 2003.
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