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.
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
Progress in our understanding of obesity has not yet spawned progress in obesity treatment, but it is probably just a matter of time before effective weight-loss medications hit the pharmacy shelves. To date, weight-loss medications have been plagued with risky side-effects and low rates of long-term efficacy. As scientists continue to unravel the complex biochemistry of obesity, new preparations will no doubt be developed, since the market for such drugs is large.
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.
Cosio-Lima, L.M., K.L. Reynolds, C. Winter, et al. Effects of physioball and conventional floor exercises on early phase adaptations in back and abdominal core stability and balance in women. Journal of Strength and Conditioning Research 17(4): 721-726, November 2003.
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.
