The Effect of Whole Milk to Improve Muscle Health in Older Women

Muscle and strength begin to noticeably decline around 50 years of age, increasing an individual's risk for disease and disability. Although changes in muscle mass ultimately depend on the balance of muscle protein synthesis (MPS) and breakdown (MPB) of muscle proteins, the latter remains relatively constant with aging. Accordingly, interventions that increase rates of MPS may combat long-term decrements in skeletal muscle mass and function. Previous research has established that an optimal diet to maintain muscle mass in elderly individuals requires relatively large amounts of high-quality protein to be consumed at each meal of the day. While this is a seemingly simple strategy, there are some barriers to increasing protein feeding in elderly individuals, particularly the cost of high-quality protein and, sometimes, difficulty with chewing/swallowing. Moreover, older adults often do not wish to consume large portions of protein in one meal.

Milk is a readily accessible, affordable and nutritious source of nutrient-dense high-quality protein. Consuming milk with each meal is an easy strategy to promote the maintenance of skeletal muscle mass with aging. There is also evidence suggesting that a higher fat content of milk can have a beneficial role in stimulating the MPS response to feeding, but there are insufficient data to recommend this strategy to elderly individuals.

The primary aim is to measure the rates of MPS in response to controlled diets providing whole milk, fat-free milk, or a control supplement (almond beverage - often marketed as an 'alternative' to milk) with each meal. All diets will provide equal amounts of energy, but the dairy interventions will provide more protein, reflecting the amount of protein provided by each beverage. The investigators hypothesize that rates of MPS will be highest in the whole milk group but that fat-free milk will still elicit a greater MPS than almond beverage. The investigators will conduct the comparison of beverages under habitual physical activity levels and under a brief period of increased physical activity (i.e., increased daily steps). Thus, the investigators will be able to determine whether MPS responses to the experimental beverages are increased in combination with physical activity. The results will provide evidence regarding the effectiveness of daily milk ingestion for the maintenance of muscle in the elderly, increasing the marketability of milk, and potentially whole milk.