Effects of Macronutrient Intake on Substrate Utilization: Potential Sex Differences (2015)
Undergraduates: Meredith Mock, Katie R. Hirsch, Erica J. Roelofs, Eric T. Trexler
Faculty Advisor: Abbie Smith-Ryan
Department: Exercise & Sport Science
PURPOSE: To explore sex differences in the relationship between habitual macronutrient distribution and substrate utilization (RER) during exercise. METHODS: Twenty-eight recreationally active subjects completed a three-day food log to assess total intake of calories, estimated energy requirements (EER), carbohydrate (CHO), fat, and protein (PRO). Respiratory exchange ratio (RER) was analyzed via indirect calorimetry during a six-minute lactate threshold cycling test. RESULTS: For men, there was a significant positive correlation between CHO and RER at 4 and 6 min (p=0.012; p=0.013), with no significant relationship between PRO and RER or fat and RER. For women, there was a significant positive correlation with PRO and RER at the end of a high-intensity bout (6 min; p=0.010) and between CHO and RER at 5 min (p=0.008). Independent of sex, macronutrient intake demonstrated a significant positive correlation with total calories (p<0.01). Evaluation of the total group EER demonstrated a positive relationship between PRO and FAT when intake was less than recommended. CONCLUSIONS: Contrary to expectation, a positive correlation between RER and PRO intake was seen in women, whereas men reported an expected relationship between RER and CHO. Future studies should evaluate long-term effects of dietary changes on exercise fuel utilization, as well as evaluate more moderate intensity exercise.