Understanding the sensitivity of muscle protein synthesis to dairy protein in middle-aged men

Although the consumption of dairy protein results in a robust increase in muscle protein synthesis (MPS), the magnitude of the increase is dependent upon the dose of protein ingested and the age of the individual. The minimum dose of dairy protein that can stimulate MPS in middle age (50.1 ± 4.5 years), a period of life during which muscle mass is typically lost, is not known. Sixteen middle-aged men (45-60 years) were randomly assigned to consume beverages containing either 10 g of milk protein (MP10) or 6 g of MP plus 20 g of carbohydrate (MP6 + CHO). A primed constant infusion of 13C6 phenylalanine was maintained and muscle biopsy samples were collected to calculate MPS. MP10 increased MPS above fasting levels for 90 min after ingestion, whereas MP6 + CHO did not increase MPS. This study demonstrates that between 6 and 10 g of MP is required to stimulate MPS in middle-aged men.