Obesity and Metabolism: Why Weight Loss Is Difficult to Sustain
Every dieter knows that keeping pounds off is even harder than losing the weight in the first place. In 1995 Jules Hirsch (1927 - ) published a landmark study that explained why lost weight tends to return. It's a matter of metabolism: reduce a person's body fat, and metabolism slows so that the body burns fewer calories to carry out the same tasks, and weight floats back up. The body bucks a change in weight in the other direction as well. Hirsch and colleagues found that when weight is gained, metabolism increases and body weight tends to reduce to its starting point.
The findings resulted from ten years of studying human subjects in the Rockefeller Hospital. With his colleague Rudolph Leibel, Hirsch carefully monitored food intake, energy expenditure, and weight changes in 18 obese men and women, and in 23 people who had never been obese. During the months that these research subjects stayed in the Rockefeller Hospital, they were fed a precisely defined liquid formula diet. First the number of calories each person needed to maintain their normal weight was established. Then some subjects consumed more calories, and others fewer, in order to gain or lose ten percent of their initial weight. Those who gained weight then went on a restricted-calorie diet in order to return to baseline. Throughout the study, the researchers tracked energy expended through normal body processes at rest, through the digestion of food, and through physical activity.
Both obese people and those who had never been obese reduced their energy expenditure when their weight was lower than normal, and burned calories faster when their weight was higher than normal. The study was quickly cited as a classic for showing, in humans, one of the ways in which body weight is regulated. It also had implications for people trying to reduce their risk of diabetes or high blood pressure by losing weight: because metabolism changes, maintaining a lower weight requires restricting calories indefinitely.
The truck is loaded with what must be consumed over a lifetime to sustain a person of average size. Illustration by Karina Aberg
Jules Hirsch received his undergraduate education at Rutgers University and earned the MD at Southwestern Medical School, University of Texas - Dallas (1948). After an internship at Duke University Hospital and residencies at Upstate Medical Center in Syracuse, NY, he joined the Rockefeller Institute in 1954. Hirsch worked first with Edward H. Ahrens to pioneer techniques for separating and studying fats in blood and adipose tissue. As head of his own laboratory, he has led the field of the biology of weight regulation. Hirsch served as Physician-in-Chief of the Rockefeller University Hospital from 1992 to 1996, and chairman of the Institutional Review Board from 1984 to 1996. He has been president of the Association for Patient-Oriented Research and the American Society for Clinical Nutrition, and contributed as an editor or editorial board member to more than a dozen journals. Among many honors and awards, Hirsch has been elected to the Institute of Medicine, and he received the Stunkard Lifetime Achievement Award from The Obesity Society in 2006.
Rudolph L. Leibel earned the AB from Colgate University (1963) and the MD from Albert Einstein College of Medicine (1967). After residencies at Massachusetts General Hospital and Children's Hospital Medical Center (Boston), and a fellowship at Massachusetts General, he joined Rockefeller University in 1978 as assistant professor. At Rockefeller he became associate director of the Pew Center of Nutrition Excellence, and he also held appointments at Cornell University Medical College. Leibel moved to Columbia University in 1997. Today he is professor of pediatrics and medicine, head of the Division of Molecular Genetics, and co-director of the Naomi Berrie Diabetes Center at Columbia University Medical Center. He serves on the editorial boards of the Journal of Clinical Investigation and International Journal of Obesity and Obesity Research, and is a member of the Institute of Medicine of the U.S. National Academy of Sciences.
Rosenbaum M, and Hirsch J. Changes in energy expenditure resulting from
altered body weight. N Engl J Med, 1995, 332: 621-628
Hirsch J. Obesity: Matter over mind? Cerebrum, 2003, 5: 7-18
Charlie Rose Interview with Jules Hirsch and Rudolph Leibel
Metabolism Found to Adjust For a Body's Natural Weight