Pennington Biomedical Research Center Scientists Study the Effects of Dietary Protein Content on Weight Gain, Energy Expenditure and Body Composition During Overeating - 01.03.2012

BATON ROUGE, LA – Researchers at the Pennington Biomedical Research Center, in results published in the current issue of the Journal of the American Medical Association (JAMA), have discovered that calories alone, not protein, have more significance on weight gain and account for the increase in body fat when individuals overeat.  

Lead investigator George Bray, M.D., Boyd Professor and Chief of the Division of Clinical Obesity and Metabolism at Pennington Biomedical, and his colleagues studied 25 healthy, weight stable young men and women (age 18-35) who were normal to slightly overweight (BMI 19 to 30 kmg²).  These individuals resided in an inpatient clinical setting for up to 12 weeks and ate an excess of 1000 kcal per day for 8 weeks, which was approximately 40% more than needed to keep their weight stable.  The study participants were divided into 3 randomized groups: 8 individuals were assigned to eat a low protein diet (5% protein), 9 were assigned to eat a normal protein diet (15% protein) and the remaining 8 were assigned to eat a high protein diet (25% protein).  Before and during the diet period, body weight and body fat were measured regularly.  Resting or basal energy expenditure was also measured weekly and the total amount of energy expenditure was measured before and at the conclusion of the study. 

Surprisingly, individuals overeating the low protein diet gained less weight (7 lb or 3.16 kg) compared to those eating the normal protein diet (13.3 lb or 6.05 kg) or high protein diet (13.5 lb or 6.17 kg).  Despite the differences in weight gain, all 3 groups added the same amount of body fat (7.1 lbs or 3.2 kg).  This discrepancy between weight gain and fattening was due to the difference in the amount of body protein that was made.  There were significant increases in body protein with both the normal and high protein diet, but the group eating the low protein diet actually lost protein from their body.

“Based on these findings among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage,” said Dr. Bray.

Effects of Overfeeding on Body Fat Composition

With the advent of the New Year, many people are turning their focus to burning off extra calories consumed during holiday overeating and not gain weight.  This idea is appealing not only to individuals, but from an evolutionary perspective as well.  The ability to waste ‘excess’ calories when eating an unbalanced diet would ensure an adequate supply of nutrients while at the same time avoiding risks to survival as a result of excess weight gain.  Obesity has become a major public health concern with more than 60% of adult Americans categorized as overweight and over 30% categorized as obese.  People who become obese have been in positive energy balance for an extended period of time.  Although a majority of Americans are overweight or obese, there are clearly a significant number who do not become obese.  As obesity develops, a number of metabolic changes occur, which may not completely reverse when weight is lost.  This may reflect difference in the way individuals handle the food they access each day, both during weight gain and weight loss.  This study was designed to determine whether the level of dietary proteins differentially affected body composition, weight gain, or energy expenditure under tightly controlled conditions in a randomized trial. 

The key finding of this landmark study is that calories are more important than macronutrients during overeating excess amounts of energy.  This study examined the hypothesis that overeating a low or high protein diet would produce less weight gain than normal protein diets. 

Pennington Biomedical Research Center Executive Director Steven Heymsfield, M.D. recognized the significant work and said, “These kinds of landmark studies help people understand the relationships between what and how much they eat and the body weight changes that follow. The unique resources available at Pennington Biomedical allow investigators to obtain answers to these types complex questions that are so important to all of us struggling to keep our weight in check.”

The findings are published in the January 4, 2012 issue of JAMA.  JAMA has been published continuously since 1883, and is an international peer-reviewed general medical journal published 48 times per year. The key objective of JAMA, which is the most widely circulated medical journal in the world, is to promote the science and art of medicine and the betterment of public health.

The research was funded in part by a grant from the U.S. Department of Agriculture.

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About the Pennington Biomedical Research Center
The Pennington Biomedical Research Center is at the forefront of medical discovery as it relates to understanding the causes of obesity, diabetes, cardiovascular disease, cancer and dementia. It is a campus of the Louisiana State University System and conducts basic, clinical and population research. The research enterprise at Pennington Biomedical includes approximately 80 faculty and more than 25 post-doctoral fellows who comprise a network of 50 laboratories supported by lab technicians, nurses, dieticians, and support personnel, and 19 highly specialized core service facilities.  Pennington Biomedical’s more than 500 employees perform research activities in state-of-the-art facilities on the 234-acre campus located in Baton Rouge, Louisiana.  For more information, see www.pbrc.edu.  

For More Information Contact:
Angela deGravelles (225) 202-5073
Dr. George Bray: george.bray@pbrc.edu
Dr. Corby Martin: corby.martin@pbrc.edu
Dr. Leanne Redman: leanne.redman@pbrc.edu