Low‐carbohydrate versus balanced‐carbohydrate diets for reducing weight and cardiovascular risk

Background Debates on effective and safe diets for managing obesity in adults are ongoing. Low‐carbohydrate weight‐reducing diets (also known as 'low‐carb diets') continue to be widely promoted, marketed and commercialised as being more effective for weight loss, and healthier, than 'balanced'‐carbohydrate weight‐reducing diets. Objectives To compare the effects of low‐carbohydrate weight‐reducing diets to weight‐reducing diets with balanced ranges of carbohydrates, in relation to changes in weight and cardiovascular risk, in overweight and obese adults without and with type 2 diabetes mellitus (T2DM). Search methods We searched MEDLINE (PubMed), Embase (Ovid), the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science Core Collection (Clarivate Analytics), ClinicalTrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) up to 25 June 2021, and screened reference lists of included trials and relevant systematic reviews. Language or publication restrictions were not applied. Selection criteria We included randomised controlled trials (RCTs) in adults (18 years+) who were overweight or living with obesity, without or with T2DM, and without or with cardiovascular conditions or risk factors. Trials had to compare low‐carbohydrate weight‐reducing diets to balanced‐carbohydrate (45% to 65% of total energy (TE)) weight‐reducing diets, have a weight‐reducing phase of 2 weeks or longer and be explicitly implemented for the primary purpose of reducing weight, with or without advice to restrict energy intake. Data collection and analysis Two review authors independently screened titles and s and full‐text articles to determine eligibility; and independently extracted data, assessed risk of bias using RoB 2 and assessed the certainty of the evidence using GRADE. We stratified analyses by participants without and with T2DM, and by diets with weight‐reducing phases only and those with weight‐reducing phases followed by weight‐maintenance phases. Primary outcomes were change in body weight (kg) and the number of participants per group with weight loss of at least 5%, assessed at short‐ (three months to < 12 months) and long‐term (≥ 12 months) follow‐up. Main results We included 61 parallel‐arm RCTs that randomised 6925 participants to either low‐carbohydrate or balanced‐carbohydrate weight‐reducing diets. All trials were conducted in high‐income countries except for one in China. Most participants (n = 5118 randomised) did not have T2