Abstract
Very-low-calorie ketogenic diets (VLCKDs), more recently renamed very-low-energy ketogenic therapy (VLEKT), are being used with increasing frequency in obesity management and metabolic medicine.1-3 These interventions combine marked caloric restriction, typically below 800 kcal per day, with severe carbohydrate restriction, usually below 50 g per day, to induce nutritional ketosis and a controlled protein intake, generally within medically supervised programs.1,2 Current European recommendations, together with the consensus document from the Italian Society of Endocrinology, usually calculate protein prescription according to ideal body weight rather than actual body weight. 1,2 In clinical practice, ideal body weight is often used mainly for practical reasons. In severe obesity, calculations based directly on actual body weight often generate protein prescriptions that appear disproportionate to the metabolic contribution of adipose tissue. Ideal body weight has therefore become a convenient clinical reference. Ideal body weight is an anthropometric estimate rather than a direct measure of metabolically active tissue. It does not quantify skeletal muscle mass, organ tissue, extracellular water, or fat-free mass. Protein turnover and resting energy expenditure are more closely linked to lean tissue compartments than to body weight itself.4-6 During severe caloric restriction, preserving lean mass becomes clinically relevant, particularly when weight loss occurs rapidly. The issue becomes even more evident in patients with marked heterogeneity in body composition. Older adults and individuals with sarcopenic obesity may differ substantially in skeletal muscle reserves, inflammatory burden, anabolic responsiveness, and resting energy expenditure despite similar anthropometric characteristics. A single anthropometric parameter such as ideal body weight cannot adequately reflect the wide variability in body composition and skeletal muscle mass observed among individuals with obesity. This article discusses the physiological rationale underlying protein prescription during VLEKT, with particular attention to the limitations of ideal-body-weight-based approaches and the potential relevance of body composition assessment.