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Diet trends come and go, from low-fat to low-carbohydrate, but which diet plan is better for weight loss? A recent study reports the results of a diet plan comparison.

A recent study published in the Journal of the American Medical Association has conducted a meta-analysis to estimate the relative effectiveness of different diets that have previously been tested in clinical studies for weight loss. The study determined the weight loss outcomes, and compared them based on either macronutrient composition (e.g. low-fat vs low-carbohydrate), or compared between trade-marked diets (e.g. Jenny Craig).

Included in the meta-analysis were clinical trials that consisted of participants who were either overweight (BMI 25-29) or obese (BMI ≥30), and were 18 years of age or older. The primary outcomes were weight loss and BMI at 6 and 12 month follow up. Dietary programs that were included consisted mostly of whole foods (some meal replacement was allowed), however no medications or supplements were included. The study accounted for exercise regimes, in addition to behavioural support that was provided in some of the clinical trials. Overall, the meta-analysis included 48 clinical trials, with a variety of 11 different diet brands. The participants in these trials comprised a total of 7286 people, with a median weight of 94.1kg, and median BMI of 33.7.

When comparing diet classes based on macronutrient concentration, the study revealed that at 6 months follow up all diets were better than no diet. The low carbohydrate diets resulted in a median difference in weight loss of 8.73kg, while low fat diets resulted in a median difference of 7.99kg. Low carbohydrate diets were superior to all other diet classes for weight loss, however not significantly superior to low fat diets. At 12 months follow up, low carbohydrate and low fat diets continued to show the greatest results.

When comparing different branded diets, the study revealed that all diets resulted in weight loss at the 6 month follow up when compared to no diet. The study reported that the branded diets: Ornish, Rosemary Conley, Jenny Craig, and Atkins were associated with the greatest weight loss at the 12 month time-point. In addition, the study showed that both exercise and behavioural support were associated with a greater degree of weight loss.

Overall, the study reported a significant amount of weight loss with any of the low carbohydrate or low fat diets. The statistical differences between the branded diet plans were small and therefore may not be of great importance. The authors of the study state that the Joint Guidelines from the American Heart Association, the American College of Cardiology, and the Obesity Society have also reviewed diet plans and conclude similar effectiveness of various popular diets. The authors of the study therefore suggest that adherence is of greatest importance when it comes to weight loss, and people should chose a diet plan that they have the greatest chance of sticking with for a long period of time, rather than beginning a diet that is restrictive and does not fit their personal tastes, or cultural constraints.


Johnston, BC, Kanters, S, Bandayrel, K, Wu, P, Naji, F, Siemieniuk, RA, Ball, GDC, Busse, JW, Thorlund, K, Guyatt, G, Jansen, JP, Mills, EJ. “Comparison of Weight Loss Among Named Diet Programs in Overweight and Obese Adults:  A Meta-analysis”JAMA. 2014;312(9):923-933.

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Written by Deborah Tallarigo, PhD

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