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Randomized controlled trial of the Medifast 5 & 1 Plan for weight loss



The Medifast 5 & 1 Plan (MD) is a portion-controlled, nutritionally-balanced, low-fat weight-loss plan. We studied the effects of MD compared with a reduced-energy, food-based diet (FB) on body weight, waist circumference, fat mass and other measures in adults.


We conducted a two-parallel-arm, randomized, controlled trial comparing MD to FB over 52 weeks. A total of 120 men and women aged 19–65 years with BMI 35 and 50 kg m−2 were randomized to MD (n=60) or FB (n=60). Follow-up included a 26-week weight-loss phase and 26-week weight-maintenance phase. Anthropometric, body composition, biochemical and appetite/satiety measures were performed at baseline and at 26 and 52 weeks. An intention-to-treat, linear mixed models analysis was the primary analysis.


Fifty MD subjects (83.3%) and 45 FB subjects (75.0%) completed the study on assigned treatment. At 26 weeks, race-adjusted mean weight loss was 7.5 kg in MD subjects vs 3.8 kg in FB subjects (P=0.0002 for difference); reduction in waist circumference was 5.7 cm in MD vs 3.7 cm in FB (P=0.0064); and fat mass loss was 6.4 kg in MD vs 3.7 kg in FB (P=0.0011). At 52 weeks, the corresponding reductions were 4.7 vs 1.9 kg (P=0.0004); 5.0 vs 3.6 cm (P=0.0082); and 4.1 vs 1.9 kg (P=0.0019) in MD and FB subjects, respectively.


In obese adults, MD resulted in significantly greater reductions in body weight and fat compared with an FB diet for 1 year after randomization.

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The authors acknowledge Medifast, Inc., Owings Mills, MD, for their support of the study. We acknowledge the Metabolism/Human Physiology Core Laboratory of the Nutrition Obesity Research Center, Diabetes Research and Training Center, and Center for Clinical and Translational Science at UAB (grant nos. UL1RR025777, P60DK079626, and P30DK56336, respectively) and those who performed the glucose and hs-CRP assays: Maryellen Williams and Cindy Zeng. We also acknowledge the Bioanalytical Redox Biology Core of the Diabetes Research and Training Center at UAB and those who performed the LPO assay: Gin Chuang, Kelley Johnston, and Douglas R. Moellering, PhD. Finally, we thank Kathryn Kaiser, PhD, for her critical review of the manuscript.

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Correspondence to J M Shikany or D B Allison.

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Dr Allison has, anticipates, or has had financial interests with the following: Paul, Weiss, Rifkin, Wharton & Garrison, LLP; Kraft Foods, Inc., and Nutrition Impact, LLC and has received consulting fees from Medifast. The remaining authors declare no conflict of interest.

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Shikany, J., Thomas, A., Beasley, T. et al. Randomized controlled trial of the Medifast 5 & 1 Plan for weight loss. Int J Obes 37, 1571–1578 (2013).

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  • meal replacements
  • weight-loss diets
  • weight maintenance

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