Obesity in developing countries compares to U.S. yo-yo dieting

06/08/04

ANN ARBOR, Mich.---The sad irony of obesity in developing, food-starved nations has not gone unnoticed by scientists.

In a new report, a University of Michigan researcher attempts to explain the odd co-existence of malnourishment and obesity by drawing comparisons to the yo-yo dieter syndrome, where the body compensates for starvation by storing fat for later.

The paper, "Reduced Rate of Fat Oxidation: A Metabolic Pathway to Obesity in the Developing Nations," by anthropology professor A. Roberto Frisancho, appeared in a recent issue of American Journal of Human Biology.

That both malnourishment and obesity exist simultaneously in developing populations seems counterintuitive, especially when the reasons for obesity in developing nations such as the United States are inactivity and excess fat intake. Those conditions, especially the latter, don't exist in developing nations.

"In the same household, you can have a chubby kid and a starving kid," Frisancho said. He argues that obesity in developing nations is a result of the body's attempts to cope with childhood malnourishment. The phenomena is similar to yo-yo dieting, where dieters who have deprived themselves gain weight at faster rates than non-dieters when they begin eating normally again.

Under normal nutritional conditions, humans only absorb about 80 percent of the nutrients from the food they eat, and the rest of the nutrients pass through the body. But when deprived of nourishment, the body becomes a super efficient machine, Frisancho said, pulling all the nutrients from the food for energy. Further, because humans need a certain percentage of body fat reserves to stay alive and because it takes more work for the body to burn fat than carbohydrate, the body in starvation mode learns to burn carbohydrate for energy and to store fat, rather than to use the energy for growth.

When the malnourished person begins eating normally again, the body does not re-adapt. Instead, it keeps storing fat as if malnourished. It also keeps pulling 100 percent of nutrients from the food.

"It's a byproduct of past adaptations. The same mechanism that helps them survive makes them fat," Frisancho said. It works the same way for yo-yo dieters.

"After you stop dieting, your system is already very efficient and you can't change it back," he said.

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