High dietary fat intake increases fat oxidation and reduces skeletal muscle mitochondrial respiration in trained humans.
Study Goal
The researchers aimed to determine whether adaptations in fat oxidation and carbohydrate metabolism from high-fat, low-carbohydrate diets are driven by high fat intake or low carbohydrate availability.
Results Summary
The study found that high dietary fat intake increased whole-body fat oxidation and reduced skeletal muscle mitochondrial respiration, which returned to baseline after reintroducing carbohydrates. These effects were attributed to high fat intake rather than low carbohydrate availability.
Population
8 male cyclists
Effective Dosage
High-fat diet (>65% energy intake), high-protein diet (>65% energy intake), with carbohydrate intake clamped at <20% energy intake
Duration
5 days per dietary intervention
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
High-fat, low-carbohydrate (CHO) diets | increase | whole-body rates of fat oxidation | - | - | increase | #1 |
High-fat, low-carbohydrate (CHO) diets | decrease | CHO metabolism | - | - | down-regulate | #2 |
5 d of a high-fat diet (HFAT; >65% EI) with CHO intake clamped at <20% EI | decrease | skeletal muscle mitochondrial respiration supported by octanoylcarnitine and pyruvate | 8 male cyclists | - | decreased | #3 |
5 d of a high-fat diet (HFAT; >65% EI) with CHO intake clamped at <20% EI | decrease | uncoupled respiration | 8 male cyclists | - | decreased | #4 |
5 d of a high-fat diet (HFAT; >65% EI) with CHO intake clamped at <20% EI | increase | rates of whole-body fat oxidation during exercise | 8 male cyclists | - | were higher | #5 |
After 1 d of high-CHO diet intake | no change | mitochondrial respiration | HFAT condition participants | - | returned to baseline values | #6 |
After 1 d of high-CHO diet intake | no change | rates of substrate oxidation | both conditions participants | - | returned toward baseline | #7 |
High dietary fat intake | decrease | mitochondrial respiration | - | - | contributes to reductions | #8 |
High dietary fat intake | increase | whole-body rates of fat oxidation | - | - | contributes to increases | #9 |
High-fat, low-carbohydrate (CHO) diets increase whole-body rates of fat oxidation and down-regulate CHO metabolism. We measured substrate utilization and skeletal muscle mitochondrial respiration to determine whether these adaptations are driven by high fat or low CHO availability. In a randomized crossover design, 8 male cyclists consumed 5 d of a high-CHO diet [>70% energy intake (EI)], followed by 5 d of either an isoenergetic high-fat (HFAT; >65% EI) or high-protein diet (HPRO; >65% EI) with CHO intake clamped at <20% EI. During the intervention, participants undertook daily exercise training. On d 6, participants consumed a high-CHO diet before performing 100 min of submaximal steady-state cycling plus an ∼30-min time trial. After 5 d of HFAT, skeletal muscle mitochondrial respiration supported by octanoylcarnitine and pyruvate, as well as uncoupled respiration, was decreased at rest, and rates of whole-body fat oxidation were higher during exercise compared with HPRO. After 1 d of high-CHO diet intake, mitochondrial respiration returned to baseline values in HFAT, whereas rates of substrate oxidation returned toward baseline in both conditions. These findings demonstrate that high dietary fat intake, rather than low-CHO intake, contributes to reductions in mitochondrial respiration and increases in whole-body rates of fat oxidation after a consuming a high-fat, low-CHO diet.-Leckey, J. J., Hoffman, N. J., Parr, E. B., Devlin, B. L., Trewin, A. J., Stepto, N. K., Morton, J. P., Burke, L. M., Hawley, J. A. High dietary fat intake increases fat oxidation and reduces skeletal muscle mitochondrial respiration in trained humans.