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A Diet by Any Other Name Is Still a Diet
Abstract & Commentary
Malcolm Robinson, MD, FACP, FACG, AGAF. Dr. Robinson is Emeritus Clinical Professor of Medicine, University of Oklahoma College of Medicine, Oklahoma City; he reports no financial relationship to this field of study. This article originally appeared in the April 15, 2009 issue of Internal Medicine Alert; for that publication it was reviewed by Gerald Roberts, MD. Dr. Roberts reports no financial relationship to this field of study.
Synopsis: Regardless of levels of fat, protein, and carbohydrate proportions, all diets with lowered caloric intake modestly reduced weight.
Source: Sacks FM, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med 2009;360:859-873.
There has been burning controversy regarding the "best" diet(s) for the treatment of overweight individuals, and previous studies have revealed wildly contradictory results. Most past studies were relatively small and adherence was often poor or impossible to ascertain, and few investigations lasted as long as 1 year. Even the longer and thus more realistic studies contradicted each other in terms of detecting the ideal weight-loss diet. The present authors believed that a large study was indicated to select the best weight-loss diet, and they felt that weight change over two years would be more revealing than results from shorter trials. A total of 811 particularly well-educated and motivated patients with body mass index levels between 25 kg/m2 and 40 kg/m2 were randomly assigned to one of four diets with varied targeted percentages of energy from fat, protein, and carbohydrates. Age range was from 30 to 70 years, and diabetes and unstable cardiovascular disease were exclusions, as were any medications that might affect body weight. Diets contained similar foods to the extent possible and all diets met guidelines for cardiovascular health (low cholesterol, saturated fat, and high fiber). Food was prepared at home. The diets contained dietary fat content of 20% or 40%. Carbohydrate levels were 65%, 55%, 45%, or 35%. Protein made up either 15% or 25% of calories. Primary outcomes were changes in body weight after two years in 2 x 2 factorial comparisons of high fat vs. low fat, average protein vs. high protein, and highest carbohydrate vs. lowest carbohydrate content. Patients lost an average of 6 kg after six months (7% of initial weight), but average weight began to rise after 12 months. There were no differences between any of the assigned diets and degree of weight loss, rate of ultimate weight increases later in the study, or any similar clinical parameter. Overall average weight loss across study groups was 4 kg, and almost 15% of the participants reduced body weight by at least 10%.
Attendance at offered group and individual instructional/counseling sessions was associated with weight loss at the rate of 0.2 kg/session attended. All diets improved lipid-related risk factors and fasting insulin levels. Patients were given daily meal plans, and they were instructed to record daily meal plans in a food diary and using a web-based tool. Each participant had a goal of 90 minutes of moderate physical activity per week. Laboratory data collection was extensive as were questionnaires regarding food craving, satiety, and diet satisfaction.
At two years, both low-fat diet arms and the highest-carbohydrate diet decreased low-density lipoprotein cholesterol more than the high-fat diets or the lowest-carbohydrate diet. All diets decreased triglycerides by between 12% and 17%. High-density lipoprotein levels were highest with the lowest-carbohydrate diet vs. the highest. Food craving and similar measures didn't differ between the diet arms. There were no differences in adverse events between groups. There was a high rate of patient retention, but biochemical studies indicated that none of the groups were very successful in strict adherence to their assigned diets. Patient motivation, probably best mirrored in attendance at counseling sessions, seemed most important as a marker for weight-loss success.
This important study makes it clear that no miracle diet has emerged as a panacea for the current epidemic of obesity. In fact, it would appear that any diet that successfully lowers caloric intake will lead to weight reduction. As many of us have long suspected, calories seem to be calories, regardless of their format. It is unlikely that any other study will be as well-designed or executed, and the length of the study and excellent patient retention are commendable.
As pointed out in an accompanying editorial,1 the protein intake in the study was supposed to differ by 10% but the measurement of urinary nitrogen excretion showed that the "real" intake varied by only 1% or 2%. Similar data showed that these patients, despite their excellent motivation, didn't stay on their diets. They obviously ate things that weren't on their diets, and they ate more than the diets allowed. Human nature being what it is, this shouldn't be all that surprising.
The editorial did provide readers a little hope. It described an experiment in Europe that used the combined resources of entire "villages" to get their resident children to eat more wisely and get more exercise. Amazingly, the prevalence of overweight children fell from the 17.8% in nearby communities to only 8.8%. If this approach is further documented as widely effective, we should participate (if only we can muster the self-discipline and control a wildly advertising food industry).
1. Katan MB. Weight loss diets for the prevention and treatment of obesity. N Engl J Med 2009;360: 923-925.