“In our study, three times as many people trying to lose weight were able to stick to a Mediterranean-style diet versus the low fat diet,” said study lead-author Kathy McManus, MS, RD, director of nutrition at BWH. “Motivation and adherence are very hard to sustain in any weight loss programs, but the results from this study suggest that the tastier the food, the greater overall success of the diet plan – even if it does include moderate amounts of fat.”
A moderate fat diet based on the diets of southern Europe and the Mediterranean allows for a greater variety of foods that are considered very appetizing compared with a strict, bland, low-fat diet. The main dietary fats in a typical Mediterranean diet are unsaturated. Unsaturated fat, or “healthy fat,” has been associated with lowering cholesterol.
In the study of 101 overweight men and women, half were instructed to eat a low fat diet (20% calories from fat) and half to eat a moderate fat diet (35% calories from fat, mostly monounsaturated from peanut butter, nuts, olive and canola oils). All participants were given guidelines to eat a diet of approximately 1,200-1,500 calories that was low in saturated fat and cholesterol.
Only one in five study participants could stick to the low fat diet while more than half stuck to the moderate fat diet. Both groups lost an average of 11 pounds in the first year. However the moderate fat group kept a significant amount of weight off for 18 months, whereas the low fat group did not. The moderate fat group was followed for an additional year (2 1/2 years total) and still kept a significant amount of weight off.
“My patients loved this diet because they could include favorite foods if they carefully watched portion sizes,” added McManus.
Study subjects substituted high saturated fat foods, like butter, with healthy monounsaturated fat foods, like peanut butter. They tossed nuts on their salad instead of croutons and used small amounts of full fat salad dressings.
Those in the moderate fat group increased peanut butter consumption by almost a serving (2 tablespoons) per day, increased peanut consumption by a half a serving (1/2 ounce or a small handful) and tree nuts (almonds, cashews, walnuts, etc.) by a half a serving over their baseline diets. Other foods such as healthy oils (olive, peanut and canola) and avocados were added in small amounts. Surprisingly, those on the moderate fat diet increased consumption of vegetables by one serving per day. Intake of fiber was also increased significantly, and the moderate fat group tended to eat more protein compared to their baseline diets. In contrast, the low fat group decreased their consumption of vegetables and fiber compared to baseline.
“Any low calorie diet can work in the short run, but we need to know what kind of eating pattern can sustain long-term weight loss-which is key to preventing chronic disease,” said McManus. “Obesity has become a major public health problem in this country,” said study co-author Frank Sacks, MD, of HSPH and BWH. “We must find a diet that will help American lose and keep weight off long term.”
Obesity is a chronic widespread disease of increasing prevalence, which has become a leading public health and clinical concern. It is now estimated that over 50 million people, or more than 23 percent of the adult U.S. population, are obese. Overweight and obesity are associated with major chronic illnesses, including hypertension, coronary artery disease, diabetes, arthritis, and certain forms of cancer.
The study was equally supported by the Peanut Institute, the International Olive Oil Council, and the International Tree Nut Council.
BWH is a 716-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. Internationally recognized as a leading academic health care institution, BWH is committed to excellence in patient care, medical research, and the training and education of health care professionals. The hospital’s preeminence in all aspects of clinical care is coupled with its strength in medical research. A leading recipient of research grants from the National Institutes of Health, BWH conducts internationally acclaimed clinical, basic and epidemiological studies.
The Peanut Institute is a non-profit organization that supports nutrition research and develops educational programs to encourage healthful lifestyles.