Metabolic, adherence, and sustainability outcomes of plant-based low-carbohydrate and ketogenic diets: A systematic review of clinical evidence

Plant-based adaptations of low-carbohydrate (PB-LCD) and ketogenic diets (PB-KD) have emerged as nutritional models aiming to combine metabolic efficacy, nutritional adequacy, and environmental sustainability within a One Health framework. These regimens may align human and planetary health goals, especially in long-term therapeutic contexts such as GLUT1 deficiency or drug-resistant migraine, where ketogenic approaches are established. However, evidence on the integration of plant-based principles into carbohydrate-restricted diets remains limited, particularly regarding sustainability and long-term feasibility. To critically assess the effects of PB-LCD and PB-KD on metabolic outcomes, adherence, and sustainability indicators in adults with overweight, obesity, or metabolic disorders. A systematic search of PubMed/MEDLINE, Embase, Cochrane Library, Web of Science, and Google Scholar (January 2000-March 2025) identified randomized controlled trials testing predominantly plant-based low-carbohydrate diets. Methodological quality was assessed with the Cochrane RoB 2 tool, and evidence certainty was graded using GRADE. Primary outcomes were body composition, glycemic and lipid profiles; secondary outcomes included adherence and sustainability measures. Seven RCTs (n = 976; duration 4-52 wk) were included. Both PB-LCD and PB-KD significantly reduced body weight (-5 to -7 kg), LDL-cholesterol, and HbA1c, with effects comparable or superior to control diets. GRADE certainty was moderate for weight and lipid parameters and moderate-to-low for glycemic control. Adherence was high in controlled settings but declined in free-living conditions. PB-LCDs showed better long-term feasibility, whereas PB-KDs induced stronger short-term effects but required supervision. Only one study quantified greenhouse gas emissions (-0.63 kg CO₂/d). Sustainability evidence was very low. PB-LCDs and PB-KDs are clinically effective, nutritionally safe, and potentially sustainable models for metabolic improvement, though long-term integrative trials are needed.