Effects of protein supplementation during prolonged exercise at moderate altitude on performance and plasma amino acid pattern

Abstract

The effects of two levels of protein intake on muscle performance and energy metabolism were studied in humans submitted to repeated daily sessions of prolonged exercise at moderate altitude. For this purpose, 29 healthy males, were exposed to seven successive stages of ski-mountaineering at altitudes between 2500 and 3800 m, and to an isocaloric diet (4000 kcal.day-1, 16,760 kJ.day-1) with either 1.5 g.kg-1.day-1 (C group, n = 14), or 2.5 g.kg-1.day-1 (PR group, n = 15) protein intake. Measurements made after the ski-mountaineering programme did not show any change in body mass. The peak torque during maximal isometric voluntary contraction (MVC) of the quadriceps muscle was unaffected by the repeated exercises, whereas the endurance time at 50% MVC was decreased in PR subjects (-26.8%, P < 0.001). Increased levels of both free fatty acids (+ 147%, P < 0.001) and glycerol (+ 170%, P < 0.001) observed in C subjects would suggest that lipolysis was enhanced after the repeated exercise. The plasma amino acid pattern was altered after completion of the ski-mountaineering programme; the plasma concentration of the three branched-chain amino acids (BCAA) was significantly decreased in C subjects, whereas the higher level of protein intake (PR group) greatly minimized the exercise-induced decrease in serum BCAA.

Body composition at high altitude: a randomized placebo-controlled trial of dietary carbohydrate supplementation

“…Thus, the results presented herein are particularly relevant to those people similarly acclimatizing to altitudes of '5500 m. Admittedly, higher calorie intake can be obtained with a high-fat supplement, but palatability would be poor. Interestingly, alternative macronutrient dietary manipulations at a high altitude have also been unsuccessful; studies of increased protein intakes have failed to abate body mass loss and have even had detrimental effects, including decreases in carbohydrate intake and in physical performance (47)(48)(49). Another study used a solid food carbohydrate supplement, but total energy intake did not increase (44).…”

Metabolic Response to Provision of Mixed Protein-Carbohydrate Supplementation during Endurance Exercise

“…Few studies have explored the integrated response of substrates and hormones when intact protein is consumed during endurance exercise. Studies that have compared traditional carbohydrate supplements to protein or amino acid supplements have sought to demonstrate that protein-based supplements establish a less catabolic environment by (a) providing substrate directly, thus minimizing utilization of endogenous stores of glycogen and protein (2,7), and (b) enhancing the balance of anabolic to catabolic hormones-that is, increasing testosterone while decreasing cortisol (5,6,31). The efficacy of branched-chain amino acid (BCAA) mixtures in improving performance has been investigated on two levels, first via amino acid regulation of muscle protein metabolism (14,21) and, second, with regard to the central fatigue hypothesis (9).…”

Nutritional Strategies for the Preservation of Fat Free Mass at High Altitude

“…In ski mountaineers supplemented with 1.5 g or 2.5 g casein protein/day for seven days at 2500–3800 m, body mass did not change. However, 50% maximal voluntary contraction endurance of the quadriceps muscle post-skiing was decreased with the high protein dose [57]. In summary, under normoxic conditions when in energy balance, evidence suggests increasing protein intake has no further advantage on increasing FFM.…”

“…Increased satiety is considered a favorable consequence of high protein intake for sea level weight loss (dieting). However, adding more protein could potentiate the problem of blunted appetite at altitude [62] and further deplete glycogen levels and impair performance, particularly if protein consumption reduces carbohydrate intake [46,57]. Currently, no research has been conducted evaluating the effects of protein supplementation on satiety at altitude.…”