Effects of pork protein ingestion prior to and following performing the army combat fitness test: markers of muscle soreness and catabolism

ABSTRACT

Background

Military personnel engaged in intense activities must consume enough quality protein in their diet to maintain protein balance and promote recovery. Plant-based proteins are considered lower-quality protein sources than animal proteins due to their lower amount of essential amino acids (EAA) and only containing trace amounts of creatine. The purpose of the study was to determine whether ingestion of military-style meals-ready-to-eat (MREs) containing plant-based (Plant) or pork-based (Pork) sources or protein would affect recovery after the Army Combat Fitness Test (ACFT).

Methods

Twenty-three (n = 23) Corps of Cadets members participated in a randomized, double-blind, placebo-controlled, and crossover-designed study where they consumed Plant or Pork protein containing MREs. Participants donated a blood sample and consumed a pre-exercise meal on testing days. After four hours, participants performed the ACFT. Participants were then fed 3 MREs daily containing ≈ 1,250 kcals, 145 g carbohydrate, 45 g protein, 60 g fat, providing 1.7 g/kg/d of protein. Plant-based MREs contained 15.2 g/d (0.20 g/kg/d) of EAA and 0.215 g/d (0.003 g/kg/d of creatine) compared to 22.9 g/d (0.31 g/kg/d) of EAA and 1.82 g/d (0.024 g/kg/d) of creatine in the pork-based MREs. Participants returned to the lab in a fasted condition at 0600 with 24-hour urine samples after 24, 48, and 72 hours of recovery. Blood and urine samples were evaluated for markers of catabolism. Muscle soreness was assessed using an algometer at three locations on the thigh. On day 3, participants repeated the ACFT four hours after consuming an MREs. Data were analyzed using general linear model statistics and percentage changes from baseline with 95% confidence intervals.

Results

Percentage changes in perceptions of muscle soreness were significantly lower when consuming pork-based MREs. A significant interaction effect was observed (p = 0.012, η_p² = 0.063, moderate effect) in urine nitrogen and creatinine excretion with values significantly lower when consuming pork-based MREs, indicative of less protein degradation. The stress hormone cortisol decreased from baseline after 48 and 72 hours with pork-based MRE ingestion while remaining unchanged with plant-based MREs. The testosterone/cortisol ratio increased after 48 hours, indicating a more anabolic status when consuming pork-based MREs.

Conclusion

Consuming MREs containing pork as the protein source after intense training attenuated perceptions of muscle soreness and protein degradation markers and catabolism markers. These findings suggest that the protein quality of the MREs can affect recovery from intense military-style exercise despite consuming recommended amounts of protein for active individuals. MREs should contain high-quality protein sources or be supplemented with 6–10 g/d of EAA and 2–3 g/d of creatine monohydrate to offset dietary deficiencies, particularly in military personnel following a plant-based diet. Registered clinical trial #ISRCTN47322504

Figure 1.

Percent changes in muscle soreness ratings, urine nitrogen and creatinine excretion, and hormonal markers of anabolism and catabolism. Data are means and ± 95% confidence intervals. † = p < 0.05 (‡ = p > 0.05 to p < 0.10) difference from baseline value. * = p < 0.05 (⁑ = p > 0.05 to p < 0.10) difference between treatments.

Funding Statement

This study was funded by the United States Department of Agriculture (USDA) National Pork Board as part of a Department of Defense subaward to Texas A&M University.