Effect of Resistance Exercise and Protein Timing on Lipolysis and Fat Oxidation in Resistance-Trained Women

The number of women participating in resistance training has increased from 14.4% in 1994 to 21.0% in 2010 (418). Resistance training is known to enhance body composition (20); however, the effects of an acute bout of resistance exercise (RE) on subcutaneous abdominal adipose tissue (SCAAT) glycerol release (lipolysis) and whole-body substrate utilization have only been documented in men (272). In fact, both RE and protein (alone and in combination) have been shown to improve lipolysis and fat oxidation leading to improved overall body composition (20). Mounting evidence suggests there are metabolic benefits of pre-sleep protein (PRO) consumption (65, 101, 190, 193, 274, 276). However, only one study directly assessed the effects of pre-sleep PRO consumption on SCAAT lipolysis and whole-body substrate utilization, and it was performed in overweight/obese men (190). Furthermore, few pre-sleep PRO studies to date have been directly compared to PRO consumed at other times of the day (17). Thus, it is difficult to interpret if the benefit is from pre-sleep feeding or simply increased daily PRO intake. PURPOSE: Therefore, the purpose of the current study was to assess the effects of RE (Aim 1) and pre-sleep versus daytime PRO consumption (Aim 2) on SCAAT lipolysis and whole-body substrate utilization in resistance-trained women. For Aim 1, a one-way ANOVA was used to analyze changes in interstitial GLY concentrations, metabolic rate, and plasma biomarkers around RE compared to baseline (BL) (BL, Mid-RE, post-RE). For Aim 2, a repeated measures ANOVA was used to compare the differences in interstitial GLY concentrations, metabolic rate, and plasma biomarkers between PRO-PLA and PLA-PRO conditions. If a significant finding was noted, a Tukey HSD post-hoc analysis was used to locate where the difference existed. Data were analyzed using SPSS (Version 25) with significance set at p<0.05, and are presented as mean ± standard error (SE). METHODS: Thirteen healthy, resistance-trained, eumenorrheic women (age, 22±3 years) volunteered to participate in the study. Participants reported to the laboratory on five occasions: pre-testing and familiarization of maximal testing (Visit 1), maximal testing (Visit 2), familiarization (Visit 3), and two experimental visits (Visits 4 and 5). For each of the experimental visits, participants came to the laboratory in a fasted state, and microdialysis probes were inserted into the SCAAT to measure lipolysis. Participants then performed a full-body RE session consisting of the following exercises in this order: squat, bench press, Romanian deadlift, bent-over row, shoulder press, reverse lunges. After RE on each of the experimental visit days, participants were randomized to consume either daytime PRO (30 grams of casein protein) 30 minutes post-RE and pre-sleep non-caloric, sensory-matched placebo (PLA, 0 grams of casein protein) (PRO-PLA), or daytime PLA and pre-sleep PRO (PLA-PRO), switching the order of the supplements on the following visit. Participants slept in the laboratory for overnight assessment of lipolysis and dietary intake was controlled by providing participants with breakfast, lunch and dinner (Vale Food Inc., Tallahassee, FL) based on their calculated caloric needs. Resting energy expenditure (REE) and respiratory exchange ratio (RER) were measured at baseline, post-RE, post pre-sleep supplement and the next morning of PLA-PRO and PRO-PLA conditions. Fasted blood samples were collected from the antecubital vein on three occasions for Aim 1: 1) baseline, 2) mid-RE, and 3) post-RE. In addition, blood samples were collected on three occasions for Aim 2: 1) 30 minutes after the daytime supplement (fed); 2) 30 minutes after the pre-sleep supplement (fed), and; 3) the next morning (fasted). Non-esterified fatty acids (NEFA), glycerol, glucose, and insulin were measured for Aim 1 and 2, while catecholamines (CATs) and growth hormone (GH) were measured only for Aim 1. RESULTS: After RE, REE (baseline: 1554±193; post-RE 1772±257 kcal/d; p=0.001) and fat oxidation (FatOx) (baseline: 5.64±0.23; post-RE: 7.57±0.34 g/hr; p<0.001) significantly increased (Aim 1, n=13). Additionally, SCAAT interstitial glycerol concentration was significantly higher at mid-RE (1177.4±667.1 µM, p=0.049) and post-RE (1197.3±1063.4 µM, p=0.01), compared to baseline (596.7±452.3 µM) (n=13). There were no significant changes in plasma biomarkers NEFA, glycerol, glucose, insulin, CATs, or GH. There was a significant increase in REE in both groups compared to baseline but no difference between groups. There was a significant increase in FatOx in PLA-PRO only after consuming the nighttime supplement (baseline: 5.64±0.23 g/min; PLA-PRO: 6.59±0.32 g/min, p=0.02), but no differences between PLA-PRO and PRO-PLA conditions. There were no other differences in lipolysis, metabolic measures, or plasma biomarkers between PRO-PLA or PLA-PRO conditions. RE increased lipolysis and FatOx mid-RE and post-RE in resistance-trained women. There were no differences in fat metabolism throughout sleep between PLA-PRO and PRO-PLA. CONCLUSION: Our findings indicate that RE improves fat metabolism potentially mediated by increases in CATs and GH. Consuming daily PRO 30 min post-RE or 30-min pre-sleep has no additional influence on fat metabolism (does not blunt overnight lipolysis) in resistance-trained women. This study was supported by a research grant from Friesland Campina® and Dymatize® Nutrition.