Document Type

Article

Publication Title

Journal of the International Society of Sports Nutrition

Abstract

The International Society of Sports Nutrition (ISSN) has developed an official position on diets for body weight reduction. This critical analysis of the literature is intended to provide a scientific foundation for practitioners, coaches, and trainees regarding the effects of the major diet types in adults who are generally healthy, physically active, and/or athletic, while drawing from clinical research in those with overweight/obesity, when relevant. This position stand does not address acute dehydration-based weight cutting, pharmacotherapy (i.e. GLP-1RAs), or bariatric surgery. The following 15 points constitute the Position Statement of the Society; the Research Committee has approved them.

  1. Diets for body weight reduction can be broadly categorized by the magnitude of the energy deficit, linearity of the deficit, and macronutrient composition. These factors need to be tailored to individual preferences, tolerances, and goals.

  2. Very-low-energy diets (< 800 kcal/day) and low-energy diets (800–1200 kcal/day) produce greater short-term weight loss but lack long-term advantages over less aggressive energy restrictions, such as calorie-controlled diets. These aggressive diets may increase lean mass loss, although adequate protein intake and resistance training may mitigate this risk. Caution is warranted about insufficiencies in vitamins, minerals, fiber, and other nutrients.

  3. The evidence at-large shows a lack of differential effects between intermittent fasting variants (alternate-day fasting, time-restricted eating, and twice-weekly fasting) and continuous energy restriction on anthropometric outcomes, although macronutrient quality plays an independent role in optimizing body composition and metabolic health.

  4. Intra-day meal frequency (as opposed to total daily nutrition) does not tend to crucially influence body weight and body fat reduction. Meal frequency may be individualized flexibly; no lower or upper limits can universally be prescribed to optimize outcomes. However, in physically active and athletic populations, distributing protein across at least three protein-rich meals (or eating occasions) per day may optimize lean mass retention and performance during sustained energy deficits.

  5. Resistance training and sufficient protein intake are indispensable mitigators of lean mass loss in a sustained caloric deficit, regardless of the diet type or variant. Total daily protein is of primary importance; specific distribution of the constituent doses is a secondary concern.

Research Highlights

  • Core Objective: This position stand critically analyzes the literature on diets for body weight reduction to provide a scientific foundation regarding the effects of major diet types in generally healthy, physically active, or athletic adults, as well as clinical research in individuals with overweight or obesity.

  • Methodology & Corpus: A comprehensive literature review was conducted using PubMed/MEDLINE and Google Scholar, with the final search executed on August 7, 2026. The search prioritized systematic reviews, meta-analyses, and randomized controlled trials using terms related to energy restriction, intermittent fasting, protein intake, low-carbohydrate diets, and adaptive thermogenesis. The evidence was appraised qualitatively without the application of a formal GRADE process.

  • Consolidated Findings: Very-low-energy diets (<800 kcal/day) and low-energy diets (800-1200 kcal/day) produce greater short-term weight loss but lack long-term advantages over less aggressive energy restrictions; intermittent fasting variants demonstrate a lack of differential effects compared to continuous energy restriction on anthropometric outcomes when net energy deficits are matched; high-protein diets comprising 20%-45% of total energy improve weight loss outcomes, with intakes of 1.2-1.6 g/kg/day being appropriate for the general population and 1.9-3.2 g/kg/day maximizing lean mass retention in resistance-trained individuals; low-carbohydrate and low-fat diets yield similar long-term weight and fat loss outcomes when energy and protein are equated; adaptive thermogenesis reduces resting energy expenditure beyond changes predicted by body composition but often attenuates substantially upon the attainment of weight stability.

  • Practical Implications: Practitioners must individualize the magnitude of the energy deficit, the linearity of the deficit, and the macronutrient composition based on personal preferences and tolerances. Resistance training and sufficient protein intake are indispensable mitigators of lean mass loss during a sustained caloric deficit. Guidance from an interdisciplinary team of health professionals and the development of home-cooked meal preparation skills are recommended for successful long-term weight management.

DOI

https://doi.org/10.1080/15502783.2026.2740266

Publication Date

9-2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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