How much protein is too much protein, and can increasing protein intake speed up ageing, shorten lifespan? “In young rodents, dietary protein restriction improves metabolic function by reducing adiposity, increasing energy expenditure, and improving glucose homeostasis. This is not due to decreased calorie intake; protein restriction actually increases food intake yet decreases fat mass and weight due to increased energy expenditure,” the review noted. Although these effects are most pronounced in males, females also show “improved metabolic health with protein restriction”. “Protein restriction remains effective when initiated late in life (18–20 months of age), increasing energy expenditure and improving metabolic health in aged mice.