¹Beth Israel Deaconess Medical Center, Center for the Study of Nutrition Medicine, Boston, MA, USA

Correspondence: George L. Blackburn, (gblackbu@bidmc.harvard.edu)

Received 3 October 2007; Accepted 8 October 2007.

This issue of Obesity includes two studies that support reduced fat consumption, Donnelly et al. and Donahoo et al. Diets with less fat (20–25%) can reduce mean energy intake by 100 kcal/day—enough to stop the growing epidemic of overweight and obesity. Our task is not to debate whether low-fat diets work, but to find ways to increase adherence to them.

Approximately two-thirds of the US adult population is overweight and one-third is obese.¹ In 2002, obesity and obesity-related complications accounted for 9.1% of US health care expenditures (or more than $92 billion), and those numbers are rising.²

Cutting dietary fat is the most efficient way to stop the obesity epidemic. With 9 kcal/g, fat is the most energy-dense nutrient. Eating less fat, particularly less saturated and trans fat, easily reduces energy intake.

This issue of Obesity includes two studies that support reduced fat consumption, Donnelly et al.³ and Donahoo et al.⁴ Each examines the typical range of western fat intake and suggests that eating more fat leads to increased energy intake and greater weight gain compared with reduced fat consumption. Diets with less fat (20–25%) can reduce mean energy intake by 100 kcal/day, or the equivalent, over the course of a year, of 10 lb—enough to stop the growing epidemic of overweight and obesity.⁵,⁶,⁷

Low-fat diets produce moderate weight loss, but questions remain as to whether such diets can be sustained. Long-term studies demonstrate that diets moderately low in fat can be maintained over time. In a 7-year follow-up, the Women's Health Initiative found that those who consumed less fat and more fruits, vegetables, and whole grains lost more weight than controls, and maintained their weight loss.⁸ The Framingham Study showed that over 40 years, a modest 5–7% decrease in dietary fat reduced total caloric intake by 150 kcal/day in men and 100 kcal/day in women.⁹,¹⁰

Health benefits from low-fat diets are not unimpressive. A 5-year study examining cancer patients in remission found that those who consumed the prototypical "Western Diet" (characterized by high intake of fat, red meat, refined grains, and desserts) showed a higher risk of recurrence than those who ate less of those foods.¹¹ The recently completed Women's Intervention Nutrition Study found that a diet low in fat (33.3 g/day vs. 51.3 g/day) and higher in fiber, fruits, and vegetables produced greater weight loss over 5 years, and reduced breast cancer relapse rates by 24%.¹²

Unlike a diet high in carbohydrates and proteins, a high-fat diet works against the goals of healthy eating. Satiety hormones in the gut, e.g., cholecystokinin and peptide-YY, normally slow gastric emptying and promote satiety in response to nutrient stimulation. With long-term intake of a high-fat diet (i.e., 58% energy), these hormones become dysregulated.¹³ Hunger increases, as does energy intake required to achieve satiety. In turn, body weight also increases.

The United States Department of Agriculture has been recommending moderate fat intake since it released its first set of nutritional guidelines in 1916.¹⁴ The American Dietetic Association,¹⁵ American Heart Association,¹⁶ National Heart, Lung, and Blood Institute,¹⁷ and the Institute of Medicine¹⁸ all recommend lifetime consumption of diets high in vegetables and moderately low in fat.

Evolution favors such a diet. For nearly 2 million years, our predecessors consumed lean meat, fish, vegetables, fruits, and nuts—low-fat diets high in fiber, proteins, and essential fatty acids. Retrospective models of Paleolithic diets estimate macronutrient content at 62% carbohydrates, 24% fat, and 14% protein.¹⁹ Whole foods and moderately low-fat diets approximate this macronutrient content. As all macronutrient-based diets produce similar long-term weight loss, it does not matter which one people choose; the key is long-term adherence and maintenance of weight loss.

Our task is not to debate whether low-fat diets work, but to find ways to increase adherence to them. We need to spread the message that moderate weight loss of 10% is an acceptable, healthy option for those who want to lose weight—an option easily achieved by cutting small amounts of fat out of each meal. This is a reasonable and realistic goal, one that can be achieved as well as sustained.