Tuesday, March 05, 2013

Insights Into Dieting Success Disparity

Have you ever wondered why some people are able to lose weight more than others? Researchers at USDA's Agricultural Research Service (ARS) Western Human Nutrition Research Center in Davis are conducting studies that may provide new insights into the underlying causes of this disparity in dieting success.

The U.S. Centers for Disease Control and Prevention (CDC) estimates 35% of adults and 18% of kids and adolescents age 6 through 19 years are overweight or obese. Both conditions are associated with increased risk of type 2 diabetes, cardiovascular disease and other chronic disorders.

The investigations, led by Nancy L. Keim and Kevin D. Laugero, were published in the journal Physiology & Behavior and may lead to successful, science-based strategies for weight management.

In one investigation, 29 obese but otherwise healthy women age 20 to 45 participated in a 12-week weight-loss regimen. The researchers assessed several factors related to weight management, including the volunteers' patterns of decision-making, and changes in their levels of cortisol, a stress-associated hormone.

The amount of weight that volunteers lost varied greatly, from zero to 27 pounds, despite the fact that all were essentially eating the same foods in the calorie-controlled meals provided to them at the nutrition center. Keim noted the finding underscores the need for weight-management plans that are even more individualized than those available today.

The scientists also found dieters who lost the most weight were those who scored the highest on the Iowa Gambling Task (IGT), a standard test that helps assess, for example, decision-making and the ability to resist the temptation of short-term, immediate rewards in favor of longer-term benefits.

Though the idea of using the IGT in obesity research is not new, the ARS investigation is the first to show, in what scientists refer to as a controlled-feeding weight-loss trial, an association between IGT scores and diet-induced weight loss.

Cortisol findings were based on concentrations of the hormone in saliva samples collected throughout the day on two different test dates. The scientists found that volunteers' cortisol concentrations generally increased from the beginning to the end of the 12 weeks of dieting.

Laugero noted increases in cortisol concentration have long been regarded as a reliable indicator of psychological stress, and that stress is considered to be a contributing factor to dieters' relapsing back to old eating habits and regaining weight.

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