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New ARS studies of obesity could help put dieting on a more scientific basis. Photo courtesy of Microsoft clipart.

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Scientists Explore Brain, Cortisol, and Weight Loss Connections

By Marcia Wood
March 4, 2013

Weight-management studies led by U.S. Department of Agriculture (USDA) scientists are helping determine why some dieters lose more weight than others, and are more successful in keeping it off.

Chemist Nancy L. Keim and nutrition scientist Kevin D. Laugero are conducting the investigations, which may lead to successful, science-based strategies for weight management. Both scientists are with the USDA's Agricultural Research Service (ARS) Western Human Nutrition Research Center in Davis, Calif. ARS is the USDA's chief intramural scientific research agency.

Given America's obesity epidemic, weight-management research is timely and relevant. The U.S. Centers for Disease Control and Prevention estimate that 35 percent of adults and 18 percent of kids and adolescents age 6 through 19 are overweight or obese. Both conditions are associated with increased risk of type 2 diabetes, cardiovascular disease and other chronic disorders.

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 that the finding underscores the need for weight-management plans that are even more individualized than those available today.

The scientists also found that 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 that 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.

Keim and Laugero collaborated in the study with physiologist and research leader Sean H. Adams and physiologist Marta D. Van Loan, both with the nutrition center, and with postdoctoral researcher Megan G. Witbracht of the University of California-Davis.

The research, published in Physiology and Behavior, was funded by ARS, the university, the National Dairy Council, the Dairy Council of California, and the National Institutes of Health.

Read more about this research in the March 2013 issue of Agricultural Research magazine.