Abstract / Summary
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.6) For the general population, a daily protein intake of 1.2–1.6 g/kg BW is appropriate for supporting total body weight and fat loss, physical activity, and imparting benefits to musculoskeletal and cardiometabolic health.7) Daily protein intakes ranging 1.6–2.2 g/kg BW combined with resistance training may optimize muscle anabolism, while higher intakes of 1.9–3.2 g/kg BW can maximize lean mass retention in lean, resistance-trained individuals sustaining hypocaloric conditions.8) The dietary carbohydrate‒fat proportion can be individualized to personal preference for the goal of weight loss, since the range of ketogenic to low-fat diets performs similarly.9) Ketogenic diets are effective at bodyweight and body fat reduction, but they also tend to decrease fat-free mass to a greater degree than higher-carbohydrate comparators, particularly in shorter trials where glycogen and total body water shifts can influence estimates.10) Adaptations to weight loss can be physical, physiological, and/or behavioral, and converge toward reducing energy expenditure to fulfill the body’s drive toward neutralizing disruptions to homeostasis imposed by the caloric deficit.11) Adaptive thermogenesis is a reduction in resting energy expenditure beyond that predicted by changes in body composition. It can occur in response to hypocaloric conditions and weight loss, but it is not an inevitable response, and it may attenuate substantially upon attainment of weight stability.12) Metabolic adaptations that reduce energy expenditure, including adaptive thermogenesis, and impair gut microbial diversity, can often be attenuated by strategic dietary and exercise programming that foster nutrient-absorption and partitioning, and metabolic flexibility.13) A multitude of tactics can be implemented to manage and overcome plateaus. However, plateaus are also opportunities/cues to practice maintaining progress made thus far (the ultimate goal is the maintenance of a plateau).14) Guidance from an interdisciplinary team of health professionals while maintaining social support is recommended for successful weight management.15) Learning how to prepare home-cooked meals (and plan meals ahead of time through the day) puts dieters in control of their nutritional fate – and in a better position to succeed in managing their body weight and body composition.