Which diet works best to lose 3 to 9 kg in 2 years for overweight people?
An American randomized controlled trial published in the New England Journal of Medicine in 2009 by Sacks and his colleagues assessed the efficacy of 4 low-calorie diets in 811 overweight people: a high-protein diet, a low-carbohydrate diet, a high-carbohydrate diet, and a low-fat diet. After 2 years, all 4 diets resulted in similar weight loss (2.9 kg to 3.6 kg on average), and equally decreased the risk of diseases caused by excess lipids, cholesterol, triglycerides and insulin. The authors noted that the participants who attended at least two thirds of the group sessions lost 9 kg in 2 years. Could the content of a dieter’s plate matter less than his or her commitment to a program?
The Study Rationale
The debate on the efficacy of diets has been raging for a decade. Which weight-loss diet is optimal? Should one eat more meat (“protein-rich” diets)? Should one consume less sugar (“low-carb” diet)? Should fats be banned (“low-fat” diets)? All too often, the testing periods covered by diet studies are too short. A low-calorie diet typically lasts one to three months. The effects are usually analyzed at the end of the program. Some studies do propose follow-up evaluations at 3 or 6 months, but these periods remain too short, because they fail to take into account the frequent weight cycling commonly known as the “yoyo effect”. To remedy these shortcomings, this study focused on the long term effects of diets, covering a period of two years.
The testing periods covered by diet studies are too short.
Which low-calorie diet results in the greatest weight loss for overweight people over a period of 2 years?
This randomized controlled trial included 811 overweight or obese participants, who were randomly assigned to one of 4 diets: diet A (20% fat, 15% protein and 65% carbohydrates, i.e., a low-fat, average-protein diet), diet B (20% fat, 25% protein and 55% carbohydrates, i.e., a low-fat, high-protein diet), diet C (40% fat, 15% protein and 45% carbohydrates, i.e., high-fat, medium-protein diet), or diet D (40% fat, 25% protein and 35% carbohydrates, i.e., a high-fat, high-protein diet). Each diet implied a net daily loss of 750 kcal, compared to the basic diet. Additionally, each group was given conventional nutritional advice (maximum 8% saturated fats, a fibers daily minimum of 20 grams, limiting the consumption of foods causing cholesterol and favoring low glycemic-index foods), as well as overall health and weekly physical activity advice (i.e., a total of 1.5 hours of medium-intensity exercise per week). Weekly group meetings were held 3 times per month during the first 6 months, then every other week thereafter until the end of the 2-year period. The populations’ diversity was intentional; they included urban/rural, young/old and low-income/high-income individuals.
Over the 2-year period, groups who consumed 15% (-3.6 kg) or 25% proteins (-3.6 kg) experienced similar weight loss. This was true also for groups who followed either a 20%-fat or 40%-fat diet (-3.3 kg for both groups). Similarly, for individuals assigned to the 65%-carbohydrate (-2.9 kg) and the 35%-carbohydrate (-3.4 kg) diets, weight loss was almost identical. Satiety, craving and satisfaction associated with food consumption and participation in the group meetings were similar for all diets. Group session attendance was significantly associated with weight loss. All 4 diets reduced the health risks related to excess lipids, and decreased fasting insulin levels. On average, participants who attended at least 66% of the group sessions lost 9 kg in 2 years. The results of this study provide strong support for the integration of behavioral interventions into dieting programs.
The study showed that no diet could boast a weight loss advantage over another in a period of two years.
What it means for Patients
Whichever long-term diet overweight people select, its success is mostly a factor of dieters’ consistency and enthusiasm, rather than of the actual contents of their plates.
What it means for Healthcare Professionals
The key to a successful diet lies in its capacity to integrate cultural norms and preferences. This randomized controlled trial showed that no diet could boast a weight loss advantage over another in a period of two years. A high-protein diet, a low-fat diet and a low-carb diet all yielded similar results.
What it means for Researchers
Not obtaining difference expectations between non-pharmacological interventions in a randomized controlled trial can be frustrating. However, a lack of statistically significant differences between groups does not amount to a lack of results. As a case in point, the authors showed through further analysis that dieting could result in body weight losses of 3 kg in 2 years, and that group session attendance led to a total loss of 9 kg for that same period. This sub-analysis provides researchers with the basis for designing behavioral interventions to replicate this result, but with less focus on diet menus.
What it means for Policymakers
Whatever the low-calorie diet, the key factors to its success are its built-in regard for cultural preferences and the consistency with which dieters follow it. The actual contents of the dieters’ plate matter little. Conversely, support from professionals and fellow dieters in group meetings are critical for overweight people intending to lose up to 9 kg in 2 years.
Sacks FM, Bray GA, Carey VJ, Smith SR, Ryan DH, Anton SD, McManus K, Champagne CM, Bishop LM, Laranjo N, Leboff MS, Rood JC, de JongeL, Greenway FL, Loria CM, Obarzanek E, Williamson DA (2009). Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. New England Journal of Medicine, 360, 859-873.
To reference this Blog en Sante © article.
Ninot G (2014). Comparing weight loss diets. Blog en Sante, A24.
© Copyright 2014 Grégory Ninot. All rights reserved.
Thanks to Syl Billere for the English Revision