A Meal-based Comparison of Protein Quality, Complementary Proteins and Muscle Anabolism

The investigators will test the following hypotheses in middle-aged men and women (45-60) years old using a randomized, cross over design. All study objectives will be met concurrently: 1. Meals containing 30 g of high quality, predominantly beef-protein (PRO-A) will stimulate acute (i.e., single meal response) and 24 h skeletal muscle protein synthesis \[confirmatory hypothesis\] 2. Meals containing 30 g of complementary plant-based proteins (PRO-B: complete essential amino acid profile at each meal) will stimulate acute and 24 h skeletal muscle protein synthesis, but to a lesser extent than beef-protein. 3. A single meal containing 30 g of an incomplete plant-based protein source (PRO-C: lacking one essential amino acid) will fail to acutely stimulate skeletal muscle protein synthesis 4. Meals containing 30 g of plant-based protein that are incomplete at each separate meal, but complementary over a 24 h period, will fail to stimulate 24 h skeletal muscle protein synthesis. 5. Beef-and plant-based meals will have a similar effect on satiety and 24 h blood glucose \[descriptive\] If these hypotheses are correct, the investigators will demonstrate that meals containing a moderate amount of high quality protein, such as beef, are an efficient and effective way to augment a largely plant based diet and stimulate skeletal muscle protein synthesis - a prerequisite for outcomes related to physical function, performance, successful aging and metabolic health.