If obesity isn't a disorder of sedentary behavior, as Gary Taubes argues in his book “Good Calories, Bad Calories,” how does exercise fit into the equation?

As carbohydrates drive fat accumulation, he says, they increase hunger and decrease the amount of energy expended in metabolism and physical activity. So, if you eat a lot of carbohydrates, exercise helps you burn those off, but it doesn't help you maintain your weight.

“Expending more energy than we consume doesn't lead to long-term weight loss,” he concludes. “It leads to hunger.”

Exercise ameliorates the problem, but it doesn't remove the problem, which is storing the carbohydrates as fat.

Taubes says blaming sedentary behavior as a cause of obesity doesn't make sense. Obesity is associated with poverty and hard-working populations like factory workers and oil field workers. The poorer you are the more likely you are to be obese and the more likely you are to work manual labor.

“These people are much more physically active than we are,” he says. “So why are they fat?”

On the other hand, if you eat a high-protein diet, exercise may help.

Shalene McNeill, executive director of human nutrition research for the National Cattlemen's Beef Association, is certain that exercise plays a role in maintaining muscle mass, especially when coupled with a protein-rich diet.

“Exercise with a high-protein diet is helpful,” she says. “Modest changes can have a significant impact.”

McNeill cites a 2005 beef check-off-funded study by the University of Illinois' Donald Layman in the August 2005 Journal of Nutrition. The four-month weight loss trial indicates dietary protein and exercise have additive effects on body composition during weight loss in adult women.

As compared to subjects who followed a higher-carbohydrate diet with or without exercise, the subjects on the protein-rich diet with or without exercise lost more total weight, lost more fat and maintained muscle tissue. Those following the protein-rich diet also had greater reductions in triglyceride levels and maintained higher levels of good cholesterol (HDL).

McNeill says this study adds to the growing body of evidence supporting protein's beneficial role in weight management.

“You don't have to make dramatic changes in your diet to get a dramatic impact on weight management,” McNeill concludes.