For years the nation’s expanding girth has been blamed on lazy lifestyles. If more of us would just get off the couch and get moving, the thinking goes, we wouldn’t have to worry about weight loss plans and diet books. New evidence paints a more complicated picture.

Researchers at Loyola University Health System compared African-American women in metropolitan Chicago with African women in rural Nigeria. By any measure, their lifestyles could hardly have less in common. Certainly one distinction was plain to see. The Nigerian women weighed an average of 127 pounds, compared to 184 for their counterparts in Chicago—a whopping 57 pound difference.

Yet something unexpected turned up when scientists compared physical activity. The two groups of women differed hardly at all. The Chicagoans burned an average of 760 calories a day doing physical activities. The Nigerians tallied up 800 calories. The variance was not statistically significant.

Exercise has plenty of benefits. But when people burn more calories by exercising, studies generally show, they compensate by eating more–a basic survival mechanism.  ”We would love to say that physical activity has a positive effect on weight control,” said Richard Cooper, PhD, co-author of the study and chairman of the department of preventive medicine and epidemiology, “but that does not appear to be the case.”

Tellingly, the study, which included 149 women from two Nigerian villages and 172 women from Chicago and its suburban neighbor Maywood, did turn up dramatic differences in diet. The Nigerians eat foods high in fiber and carbohydrates and low in fat and animal protein. The Chicagoans–like the average American–ate a diet top heavy in processed foods, with precious little fiber and 40 to 45 percent of calories from fat.

The new findings don’t come as a complete surprise. In a previous study of volunteers from Jamaica, Loyola researchers detected no association between activity levels and weight gain over a six-year period. Other research has shown little connection between activity and body weight.

None of this implies that gettig off the couch isn’t important. It decidedly is. But so is watching what you eat, all the more so in a world of processed foods and oversized portions. “Evidence is beginning to accumulate that dietary intake may be more important than energy expenditure level,” said Loyola nutritionist Amy Luke, PhD, who co-authored the paper. “Weight loss is not likely to happen without dietary restraint.”

©2009 PDQhealth

Tags: body weight, diet, exercise, physical activity, weight loss