Summary recent findings suggest that an elevated protein intake plays a key role in bodyweight management, through increased satiety (related to increased diet-induced thermogenesis), and its effect on thermogenesis, body composition and decreased energy efficiency. These factors are related to protein metabolism. Supported by these mechanisms, larger weight loss and subsequent improved bodyweight maintenance have been observed after high-protein diets. Increased insulin sensitivity may occur, but it is unclear whether this is owing to weight loss or type of diet. Under conditions of slight bodyweight regain (while aiming for weight maintenance), a high-protein diet shows a reduced energy efficiency related to the composition of the bodyweight regained. A high-protein diet during negative energy balance and during weight maintenance thereafter preserves, or increases, fat-free mass and reduces fat mass, thus improving the metabolic profile. As protein intake is studied at different energy intakes, absolute and relative protein intakes need to be discriminated. In absolute terms (grams per day), a normal-protein diet becomes a relatively high-protein diet if combined with negative energy balance and at weight maintenance. Therefore, ‘high protein, negative energy balance diets’ aim to keep the amount (grams) of protein ingested at the same level as consumed at energy balance, despite lower energy intakes.