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

To highlight the importance of protein quality rather than the total protein content of a meal, the investigators will demonstrate that unlike high quality proteins, a single meal containing 30 g of an incomplete protein source does not stimulate skeletal muscle protein synthesis. Secondly, the investigators will directly challenge a prevalent, but untested, assertion that has the potential to negatively impact health. The goal is to demonstrate that complementary plant-proteins (i.e., two or more incomplete protein sources) must be consumed at the same meal to stimulate protein synthesis.

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.

Eligibility Criteria:
Inclusion Criteria:

1. All races and ethnic backgrounds
2. Men and women, age 45-60 years
3. Generally healthy (see exclusion criteria)
4. Able and willing to provide informed consent
5. Ability to speak and read English (\* the study procedures, e.g., muscle biopsy, duration of each acute study, e.g. overnight stay; and multiple dietary questionnaires require sound written and spoken English)

Exclusion Criteria:

1. Sarcopenia (defined by: European Working Group on Sarcopenia in Older People, EWGSOP (44))
2. Clinically significant heart disease (e.g. New York Heart Classification greater than grade II; ischemia)
3. Peripheral vascular disease
4. Pulmonary disease
5. History of systemic or pulmonary embolus
6. Uncontrolled blood pressure (systolic BP\>170, diastolic BP\>95 mmHg)
7. Impaired renal function (creatinine \>1.5 mg/dl)
8. Anemia (hematocrit \<33)
9. Untreated thyroid disease (abnormal TSH)
10. A recent history (\<12 months) of GI bleed
11. Diabetes mellitus or other untreated endocrine or metabolic disease
12. Electrolyte abnormalities
13. Any history of stroke, hypo- or hyper-coagulation disorders
14. Recent (3 years) treated cancer other than basal cell carcinoma
15. Systemic steroids, anabolic steroids, growth hormone or immunosuppressant use within 12 months
16. Recent (6 months) adherence to a weight-loss or weight-gain diet
17. Weight change of 5% or more in previous 6 months
18. Body mass index \>30 or excess body fat that compromises muscle biopsy collection
19. Body mass index \<20 or recent history (\<12 month) of disordered eating
20. Dietary preferences or practices that preclude the consumption of the study meals
21. Acute infectious disease or chronic infection
22. Alcohol or drug abuse
23. Any other condition or event considered exclusionary by study physician
24. Pregnancy