Several studies have suggested that African-American women don't lose as much weight as Caucasian women in response to the same behavioral interventions of calorie restriction or increased physical activity, said lead investigator, James P. DeLany, Ph.D., associate professor, Division of Endocrinology and Metabolism, Pitt School of Medicine.
"At first, it was thought that perhaps the African-American women didn't adhere as closely to their calorie prescriptions or that the interventions were not culturally sensitive," he said. "But even in research projects that were designed to address those possibilities, the difference in weight loss remained."
Dr. DeLany's team decided to see if there were metabolic reasons behind the discrepancy by examining body weight changes, energy expenditure, physical activity and energy intake among 39 severely obese African-American and 66 Caucasian women who were participating in a six-month weight loss program of calorie restriction and increased physical activity. They measured body composition and daily energy expenditure at the beginning and end of the intervention period and assessed physical activity levels using multisensor activity monitors. By combining these measures, they obtained objective assessment of intake during the intervention.
The researchers found that the African-American women lost about seven pounds fewer than the Caucasian women, even though their starting body mass index, or BMI, measures were comparable and they followed as closely to the calorie restriction and activity prescriptions. But the African-American women had lower resting metabolic rates and expended less energy daily than the other group.
Calorie prescriptions are typically calculated by determining how many calories are needed to fuel the body's basic physiological processes and adding the calories needed for other activities. To maintain weight, calorie intake and output should be equal. If more calories are burned than are taken in by eating, weight loss should occur.
"We prescribe how many calories are allowed and how much activity is needed during weight loss interventions based on the premise that people of the same weight have similar metabolic rates," Dr. DeLany explained. "But to account for their lower metabolic rate, African-American women must further reduce the number of calories they eat or use up more of them with exercise in order to lose the same number of pounds in the same time span as a Caucasian woman of the same weight."
Other members of the research team are John M. Jakicic, Ph.D., of Pitt School of Education and the Physical Activity and Weight Management Research Center, Division of Endocrinology, Pitt School of Medicine; Jolene B. Lowery, M.D., now of Morehouse College of Medicine; Kazanna C. Hames, Ph.D., now of Mayo Clinic; David E. Kelley, M.D., now of Merck Sharp & Dohme Corp.; and Bret H. Goodpaster, Ph.D., now of Florida Hospital, Orlando.
The study was funded by the Commonwealth of Pennsylvania Department of Health.
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About the University of Pittsburgh School of Medicine
As one of the nation's leading academic centers for biomedical research, the University of Pittsburgh School of Medicine integrates advanced technology with basic science across a broad range of disciplines in a continuous quest to harness the power of new knowledge and improve the human condition. Driven mainly by the School of Medicine and its affiliates, Pitt has ranked among the top 10 recipients of funding from the National Institutes of Health since 1998. In rankings recently released by the National Science Foundation, Pitt ranked fifth among all American universities in total federal science and engineering research and development support.
Likewise, the School of Medicine is equally committed to advancing the quality and strength of its medical and graduate education programs, for which it is recognized as an innovative leader, and to training highly skilled, compassionate clinicians and creative scientists well-equipped to engage in world-class research. The School of Medicine is the academic partner of UPMC, which has collaborated with the University to raise the standard of medical excellence in Pittsburgh and to position health care as a driving force behind the region's economy. For more information about the School of Medicine, see www.medschool.pitt.edu.
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