Four Weeks Of A Ketogenic Diet Increases Oxygen Consumption And Fat Oxidation During Moderate-intensity Walking

Abstract

PURPOSE: Establish the time-course of changes in oxygen consumption, substrate metabolism, and heart rate during treadmill walking upon commencing a ketogenic diet. METHODS: In a randomized, parallel design, 53 men and women (mean ± SD, age: 35 ± 16 years, body mass index: 24 ± 3 kg/m2) were allocated to a moderate-sugar, moderate-carbohydrate diet [MODSUG; contribution of carbohydrate (of which sugars), fat and protein to total energy intake: 50% (15%), 35%, and 15%, respectively] a low-sugar, moderate-carbohydrate diet [LOWSUG; 50% (5%), 35%, and 15%, respectively] or a low-carbohydrate, ketogenic diet [LOWCHO; 8% (2%), 77%, and 15%, respectively] for 12 weeks. Oxygen consumption and substrate metabolism were determined by Douglas bags and heart rate using electrocardiography during submaximal walking at baseline, 4-weeks and 12-weeks of the dietary intervention. The submaximal treadmill test comprised 5-minute stages at 5.2 km/h with gradients of 0%, 3%, 6% and 9%. Data were analyzed by two-way (group x time) ANOVA with post-hoc test corrected for multiple comparisons by the Bonferroni method. RESULTS: Mean oxygen consumption rates displayed a group x time interaction (P = 0.016) whereby LOWCHO increased oxygen consumption from 17.8 ± 1.8 mL/kg/min at baseline to 18.4 ± 2.1 mL/kg/min by week 4 (P = 0.02), after which levels remained elevated at 18.4 ± 2.2 at week 12 (P > 0.05). Mean heart rate during all gradients increased with LOWCHO from 115 ± 12 beats/min at baseline to 121 ± 12 beats/min by week 4 (group x time interaction, P = 0.026; post-hoc comparison, P = 0.04), reaching 120 ± 14 beats/min at week 12 (P > 0.05). Peak fat oxidation rates increased with LOWCHO from 0.37 ± 0.18 g/min at baseline to 0.58 ± 0.25 g/min at week 4 with concomitant decreases in carbohydrate oxidation rates (group x time interaction, P < 0.001; post-hoc comparison, P < 0.001) with no further increases at week 12 (0.56 ± 0.27 g/min; P > 0.05). No such increases were observed with MODSUG or LOWSUG (all P > 0.05). CONCLUSIONS: Adaptations of oxygen consumption, heart rate and fat oxidation during walking plateau by 4 weeks of commencing a low-carbohydrate ketogenic diet, suggesting 4 weeks is sufficient to maximise metabolic adaptations to exercise with ketogenic diets. Supported by The Rank Prize Funds and Kenniscentrum Suiker & Voeding.