Influence of Habitual Protein Intake on AA Tracer Oxidation

This study employed a two-phase randomized crossover design, where participants performed both a High/Habitual protein phase and a moderate protein phase. The Habitual protein phase is designed to model resistance trained individual's habitual protein consumption by providing 2.2g/kg/d in a controlled diet. The Moderate protein phase is designed to investigate the impact of decreasing dietary protein intake to a moderate amount (1.2g/kg/d) over five days on protein metabolism. Both phases used the stable isotope L-[1-13C]Phenylalanine and metabolic trails were modelled after the indicator amino acid oxidation (IAAO) technique.

High Protein Phase The high protein phase is three days in length, with diet-controlled throughout, and a metabolic trail on day 3. Participants will perform whole-body resistance exercise on days one and three.

Moderate protein phase The Moderate protein phase is seven days in length, with MT on days three, five and seven. Dietary intake will be controlled throughout the whole phase providing either 2.2 g/kg/d of protein (days one and two), or 1.2 g/kg/d (days three through seven). Full body resistance exercise will be performed performed on days one, three, five and seven.

This phase will allow measurement of protein metabolism over five days following a decrease in dietary protein intake, and to determine the effect of dietary changes on the IAAO method.

Inclusion criteria

• Healthy, weight-trained individuals that have trained consistently for > 1 year
• Habitually dietary protein consumption of 1.9 to 3.0g/kg/d
• Train each muscle group (i.e. chest, back, legs) at least twice a week
• Body mass stable in the last month
• Meets strength relative-to-weight guidelines (adapted from Morton et al., 2016; Chilibeck et -al., 1997)

• Bench Press: - Bodyweight (kg) * 1.25
• Leg Press: - Bodyweight (kg) *4.0

Exclusion criteria

• Inability to meet health and PA guidelines according to the PAR-Q+
• Inability to adhere to any of the protocol guidelines (e.g. alcohol and caffeine consumption)
• Regular tobacco use, screened by questionnaire
• Illicit drug use (e.g. growth hormone, testosterone, etc.), screened by a survey in training log

• 1 month sedentary in the last 6 months prior to study participation
• 30 minutes of continuous cardio per exercise session
• BMI > or equal to 35
• Individual plans to increase or decrease body mass in the next 3 months
• Use of supplements (excluding whey protein), such as creatine and beta-alanine, in the last 30 days