Higher protein intake preserves lean soft tissue and promotes lipid mobilization during a 7-day very-low-calorie diet

Severe energy restriction often results in the loss of lean soft tissue (LST) in addition to fat mass. This randomized controlled trial examined the effects of differing protein energy densities on body composition and metabolic responses during a short-term, very-low-calorie diet (VLCD). Nineteen healthy young women were assigned to either a low protein group (LP, 5% energy from protein) or a protein-supplemented group (HP, 15% energy from protein). Both groups followed a 7-day regimen restricting energy intake to approximately 700 kcal/day. Both groups experienced comparable weight loss of nearly 4%, however, the LP group showed a significant decrease in LST percentage and a corresponding increase in body fat percentage, whereas these parameters remained stable in the HP group. Total ketone body concentrations increased significantly in both groups, while significant increases in free fatty acids and a broader range of individual ketone body parameters were observed in the HP group. Additionally, the HP group demonstrated significant improvements in the “Role Physical” and “Role Emotional” domains of health-related quality of life (SF-36v2), without adverse effects on sleep quality. These findings suggest that even a protein intake of 0.5 g/kg/day may help preserve LST and promote lipid metabolism compared with 0.1 g/kg/day during acute severe energy restriction, offering a safe and effective approach for short-term weight management.