Effects of ketogenic and low-carbohydrate diets on the body composition of adults with overweight or obesity: A systematic review and meta-analysis of randomised controlled trials

Background and aims: More than one-third of individuals are overweight and obese in the world. Their risks of chronic health conditions are increased, which places additional burden on their family, caregivers, and healthcare system. Dietary modification is widely used for overweight and obese individuals. We investigated the effects of ketogenic diet (KD) and low-carbohydrate diet (LCD) in improving body weight (BW), body mass index (BMI), fat mass (FM), and body fat percentage (BFP) in overweight or obese individuals.

Methods: A three-step approach was adopted for searching relevant randomised controlled trials (RCTs) across five electronic databases. Two reviewers conducted the screening, review, and quality appraisal independently. A random-effects model was used because of variations in intervention and participant characteristics. Sensitivity and subgroup analyses were conducted to assess heterogeneity and variations in the results, respectively.

Results: Thirty-three RCTs involving 2821 individuals were included. Overall meta-analysis results indicated that KD/LCD significantly reduced BW, BMI, and BFP, but not FM, in individuals with a carbohydrate intake of ≤100 g/d. Subgroup analyses revealed significant improvements in BW, BMI, and FM in individuals on KD/LCD for ≥1 month and in all parameters for those with a carbohydrate intake of ≤50 g/d. High statistical heterogeneity was noted because of variations in interventions and participant characteristics.

Conclusion: Adults with overweight or obesity should consume KD/LCD for ≥1 month and limit carbohydrate intake to ≤50 g/d. Further multicentre or multicountry RCTs are needed to improve the generalisability of our findings. We recommend integrating text messaging and evidence-based information to support interventions and ensuring stringent medical supervision throughout the intervention.

Prospero registration number: CRD42022353074.