Which Comes First, Overeating or Increasing Body Fat?

David S. Ludwig - Professor of Paediatrics, Harvard Medical School, Professor of Nutrition, Harvard School of Public Health, Physician and Researcher, Boston Children’s Hospital.

Abstract: Conventional treatment for obesity, based on the first law of thermodynamics, assumes that all calories are alike, and that to lose weight one must ultimately “eat less and move more.” However, this prescription rarely succeeds over the long term. Calorie restriction elicits predictable biological responses – including increased hunger and reduced energy expenditure – that oppose ongoing weight loss. Indeed, the prevailing ‘energy balance model’ offers no compelling explanation for what specific dietary factors have so profoundly altered the biological systems that control body weight, and the mechanism through which they operate. Why has average weight increased so rapidly among populations worldwide with stable genetic obesity risk?

The ‘carbohydrate-insulin model’ proposes a reversal in causal direction. Overeating doesn’t drive weight gain over the long term; instead, the process of storing excess body fat drives overeating. High intakes of processed carbohydrate elicit hormonal responses that cause excess energy storage in adipose tissue, leaving fewer calories for metabolically active and fuel sensing tissues. Consequently, hunger increases. and metabolic rate slows in the body’s attempt to conserve energy. From this perspective, the conventional calorie-restricted, low-fat diet amounts to symptomatic treatment, destined to fail for most people because it does not target the underlying predisposition toward excess fat deposition. A dietary strategy aiming to lower insulin secretion – focused especially on the intake of processed carbohydrates – will increase the effectiveness of long-term weight management and chronic disease prevention.

Everyone is invited to join us for a glass of wine and epidemiological networking after the seminar.

Participation is free and open to everyone. The seminar is arranged by the Section of Epidemiology and the Graduate Program in Public Health and Epidemiology.