Excess Calories, Not Proportion of Dietary Protein, Key in Causing Obesity

Laura Newman

January 04, 2012

January 4, 2012 — Excess food consumption, rather than any specific caloric mixture of protein, fat, and carbohydrates, is an important driver of obesity, and will be key in curbing it, suggests new research published in the January 3 issue of JAMA.In addition, diets with low protein (about 5% of consumption) are potentially dangerous, the study revealed, resulting in loss of lean body mass, which is protective.

"The key finding of this study is that calories are more important than protein while consuming excess amounts of energy with respect to increases in body fat," write George Bray, MD, from Pennington Biomedical Research Center, Baton Rouge, Louisiana, and colleagues. Further, the authors write: "a diet providing only 5% of energy from protein was metabolically different with a higher energy cost of weight gain compared with diets that contained 15% and 25% of energy from protein."

Eating in a Controlled Setting

Twenty-five healthy young men and women were intentionally overfed by approximately 1000 extra calories each day for more than 56 days. Overfeeding was determined by using a baseline weight stabilization evaluation. Using a single-blind, randomized controlled trial study design, patients were admitted to the inpatient metabolic unit between June 2005 and October 2007.

Patients first were put on a weight-stabilizing diet for 13 to 25 days, and then randomly assigned to 1 of 3 groups: low protein (about 5% of total diet), normal protein (15% of total diet), and high protein (25% of total diet). In comparison with the weight-stabilization treatment, the added protein provided 40% more energy intake, equivalent to 954 kcal/day (95% confidence interval [CI], 884 - 1022 kcal/day). Primary outcomes were body composition, evaluated using dual energy X-ray absorptiometry; resting energy expenditure; and total energy expenditure.

Effect of Overeating on Outcomes

Excess caloric intake alone resulted in a higher-fat body composition, according to the study. The low-protein diet proved hazardous, compared with the normal- and high-protein diets, in terms of decreased lean body mass. Specifically, the study revealed significantly less weight gain in the low-protein treatment group (3.16 kg; 95% CI, 1.88 - 4.44 kg) compared with the normal-protein (6.05 kg; 95% CI, 4.84 - 7.26 kg) or high-protein (6.51 kg; 95% CI, 5.23 - 7.79 kg; P = .002) treatment groups.

When body fat was evaluated in the 3 treatment groups, researchers found that it increased about the same, regardless of which protein group people were in. People in the low-protein group did not increase their resting energy expenditure, total energy expenditure, or lean body mass, but patients in the normal-protein and high-protein groups did (resting energy expenditure: normal-protein diet, 160 kcal/day [95% CI, 102 - 218 kcal/day] vs high-protein diet, 227 kcal/day [95% CI, 165 - 289 kcal/day]; lean body mass: normal protein diet, 2.87 kg [95% CI, 2.11 - 3.62 kg] vs high-protein diet, 3.18 kg [95% CI, 2.37 - 3.98 kg]).

In an accompanying editorial, David Heber, MD, PhD, and Zhaoping Li, MD, PhD, from the University of California, Los Angeles, stress the importance of protein in weight reduction interventions, which was underscored by the study. One strength of the study, write Drs. Heber and Li, is that it evaluated fat accumulation, not just overall weight increase and body mass index, which they contend can be misleading.

"Clinicians should consider assessing a patient's overall fatness rather than simply measuring body weight or body mass index and concentrate on the potential complications of excess fat accumulation," they write. "The goals for obesity treatment should involve fat reduction rather than simply weight loss, along with a better understanding of nutrition science."

Xavier Pi-Sunyer, MD, professor of medicine at Columbia University College of Physicians and Surgeons in New York City and director of the New York Obesity Research Center, St. Luke's Roosevelt Hospital Center, New York City, told Medscape Medical News that he was not convinced of the merits of fat composition as an alternative body mass index and weight. He was not involved in the study, but said that the "public health message was that eating too much causes weight gain."

He added, "The study would have limited public health impact because with obesity, we are trying to create a caloric deficit, not an excess." In addition, he said, "Most Americans are getting 12% to 15% of their food intake from protein," so he was not concerned about the stress on sufficient protein.

However, Jules Hirsch, MD, professor emeritus and head of the Laboratory of Human Behavior and Metabolism and physician-in-chief emeritus, Rockefeller University, New York, New York, applauded the study for driving home that "no caloric mixture, everything we've tried, nothing has been demonstrated to be causative other than excess total consumption," both in causing obesity and in designing effective interventions.

"What the paper shows is that varying the particular dietary contents is not what counts, but getting caloric count down is where we need to be," Dr. Hirsch told Medscape Medical News. In addition, he said, the study shows that "a low-protein diet has no place in the treatment or production of obesity."

Dr. Bray reported that he has been a consultant to Abbott Laboratories and Takeda Global Research Institute; is an advisor to Medifast, Herbalife, and Global Direction in Medicine; and has received royalties for the Handbook of Obesity. Corby K. Martin, MD, also of the Pennington Biomedical Research Center, reported consultancies with Bristol-Myers Squibb, Eli Lily, Elcelyx, Merck, and Philips and has received compensation from International Life Sciences Institute for manuscript preparation, travel expenses from Catapult Health, Domain & Associates, and the University of Tennessee. The other authors have disclosed no relevant financial relationships. Dr. Heber has reported that he is a counselor of the Obesity Society for Clinical Research; an advisor to POM Wonderful, Herbalife, and McCormick Spice; and has received book royalties for What Color Is Your Diet. Dr. Li has disclosed no relevant financial relationships. Dr. Pi-Sunyer has reported serving on the Scientific Advisory Board for Weight Watchers, Orexigen, Vivus, and Novo Nordisk. Dr. Hirsch has disclosed no relevant financial relationships.

JAMA. 2012;307:47-55. Article full text, Editorial extract

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