A Moderate Serving of a Lower-Quality, Incomplete Protein Does Not Stimulate Skeletal Muscle Protein Synthesis

Abstract

Objectives

Dietary proteins can be broadly characterized by their origin (animal-or plant-based) and amino acid composition (complete vs. incomplete). Meals containing > 20 g of high-quality, complete protein have repeatedly been shown to robustly stimulate skeletal muscle protein synthesis. However, breakfast in many Western countries is dominated by wheat-based products. Wheat and bread are considered a “lower-quality” incomplete source of protein, containing relatively low amounts of lysine and threonine. We hypothesized that a meal containing > 20 g of wheat-based protein would offer no anabolic advantage over a control meal containing only 5 g of plant-based protein.

Methods

In a subset of healthy, middle-aged women from our recently completed trial (n = 6/17, 53 ± 7 y, 27 ± 2 kg/m²), we measured post-prandial skeletal muscle protein synthesis,  blood glucose, insulin and appetite for 3 h following the ingestion of: i) a wheat-based protein meal (INCOMPLETE: 717 kcal,  23 g protein, 120 g carbohydrate, 16 g fat) or ii) a low protein, plant-based, control meal (CONTROL: 542 kcal,  5 g protein, 86 g carbohydrate and 23 g fat). Venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed (2.0 mmol/kg) constant infusion (0.08 mmol/(kg/min)) of L-[ring-¹³C₆]phenylalanine. All analyses were performed using established, standard techniques.

Results

Preliminary results indicate post-prandial skeletal muscle protein synthesis was similar in both cohorts (INCOMPLETE: 0.050 ± 0.012%/h vs. CONTROL: 0.054 ± 0.025%/h; p = 0.83) and consistent with fasting values historically measured by our lab. Blood glucose area under the curve (AUC; p = 0.82), insulin AUC (p = 0.85) and hunger AUC were similar in both cohorts.

Conclusions

A moderate serving of incomplete protein failed to robustly stimulate skeletal muscle protein synthesis. Consumption of a higher-quality,  completeprotein meal is likely required to acutely increase muscle protein anabolism.

Funding Sources

National Cattlemen's Beef Association