An Acute Reduction in Habitual Protein Intake Attenuates Post Exercise Anabolism and May Bias Oxidation-Derived Protein Requirements in Resistance Trained Men

Abstract

Protein recommendations for resistance-trained athletes are generally lower than their habitual intakes. Excess protein consumption increases the capacity to oxidize amino acids, which can attenuate post-exercise anabolism and may impact protein requirements determined by stable isotope techniques predicated on amino acid tracer oxidation. We aimed to determine the impact of an acute (5d) reduction in dietary protein intake on post-exercise anabolism in high habitual consumers using the indicator amino acid oxidation (IAAO) technique. Resistance trained men [n = 5; 25 ± 7 y; 73.0 ± 5.7 kg; 9.9 ± 2.9% body fat; 2.69 ± 0.38 g•kg −1 •d −1 habitual protein intake) consumed a high (H; 2.2 g•kg −1 •d −1 ) and moderate (M; 1.2 g•kg −1 •d −1 ) protein diet while training every other day. During the High protein phase, participants consumed a 2d controlled diet prior to determining whole body phenylalanine turnover, net balance (NB), and 13 CO 2 excretion (F 13 CO 2 ) after exercise via oral [ 13 C]phenylalanine. During the Moderate phase, participants consumed 2.2 g protein•kg −1 •d −1 for 2d prior to consuming 1.2 g protein•kg −1 •d −1 for 5d. Phenylalanine metabolism was measured on days 1, 3, and 5 (M1, M3, and M5, respectively) of the moderate intake. F 13 CO 2 , the primary outcome for IAAO, was ∼72 and ∼55% greater on the 1st day (M1, P < 0.05) and the third day of the moderate protein diet (M3, P = 0.07), respectively, compared to the High protein trial. Compared to the High protein trial, NB was ∼25% lower on the 1st day (M1, P < 0.01) and 15% lower on the third day of the moderate protein diet (M3, P = 0.09). High habitual protein consumption may bias protein requirements determined by traditional IAAO methods that use only a 2d pre-trial controlled diet. Post-exercise whole body anabolism is attenuated following a reduction in protein intake in resistance trained men and may require ∼3-5d to adapt. This trial is registered at clinicaltrials.gov as NCT03845569.

Links Between Testosterone, Oestrogen, and the Growth Hormone/Insulin-Like Growth Factor Axis and Resistance Exercise Muscle Adaptations

“…However, the mechanisms of lactate action on testosterone production by Leydig cells are not clear yet. While the acute response of testosterone returns to baseline rapidly post exercise and has been shown to not be elevated chronically following repeated bouts of RE (Hooper et al, 2017 ); the acute upregulation of AR mRNA and protein content can last up to 1–2 days post RE (Ratamess et al, 2005 ), thereby augmenting testosterone uptake into the muscle, and potentiating the anabolic effects of testosterone over longer periods (Murphy and Koehler, 2020 ; Tinline-Goodfellow et al, 2020 ). It therefore may be that the combined effects of acute testosterone elevation post exercise and sustained AR upregulation in the muscle may represent an additional mechanism through which RE might regulate muscle growth.…”

Protein Requirements of Pre-Menopausal Female Athletes: Systematic Literature Review

“…Moreover, it is possible that protein requirements of female endurance athletes in this review have been overestimated due to high daily protein intakes and the limitations of the nitrogen balance method for estimating protein requirements of athletes, see the review by Tipton and Witard [ 8 ]. Recent research has also indicated that the IAAO method can overestimate protein requirements in athletes with high habitual protein intakes and requires ≥5 days of dietary adaptation, which is not commonly employed by studies using this method [ 9 ]. Further research using sound methodological design is therefore required to enhance our current knowledge on protein requirements and the practical application of daily protein intake recommendations for pre-menopausal female endurance athletes across a range of contexts, such as menstrual cycle phase, energy balance status and training modality.…”

“…Due to the increased protein turnover associated with exercise, current sports nutrition guidelines for daily protein intake (1.2–2.0 g/kg/day) [ 3 ] are higher than national dietary guidelines (~0.6–0.8 g/kg/day) that are aimed at preventing nutrient deficiencies in the general population [ 4 , 5 , 6 ] rather than optimising exercise training adaptations [ 1 , 7 ]. Unfortunately, these sports nutrition guidelines [ 3 ] are limited by methodological issues that have been used to determine protein requirements in athletes [ 8 , 9 ] and are primarily based on research investigating the requirements of male athletes. Research that is primarily conducted in male athletes is then applied to female athletes on the basis of similar resting, post-exercise and post-prandial muscle protein synthesis (MPS) responses, and a lack of evidence suggesting that muscle mass influences post-exercise protein requirements [ 10 , 11 , 12 ].…”

Dietary Intake and Nitrogen Balance in British Army Infantry Recruits Undergoing Basic Training

“…These include the assumption that the metabolism of one amino acid, typically phenylalanine, represents all other amino acids [ 26 ] with discrepancies in physiological responses being observed when multiple amino acids are traced [ 53 ]. Furthermore, protein requirements estimated using the amino acid tracer method may be influenced by an individual’s habitual protein intake and subsequently result in an overestimation of the amount of protein needed per day to meet training demands [ 54 ]. Considering the limitations of measuring protein metabolism, it is acknowledged that assessing protein requirements during military training is challenging and each method has its limitations.…”