Objectives Sprint interval training (SIT) has been proposed as a time-efficient alternative to current aerobic-based exercise recommendations. A single SIT session is known has positive effects on fat metabolism by increasing post-exercise VO₂ and fat oxidation and reducing RER and carbohydrate oxidation after a single SIT bout. Short-term high fat diet is known has positive effects on fat oxidation pre- and post- submaximal exercise session. However, combination of a single SIT session and short-term high fat diet effects on fat oxidation was not studied before. The aim of the study was to investigate the effect of short-term different diet modifications (high fat and high carbohydrate) on fat oxidation after a SIT bout in healthy young trained men and to compare the effects with recreationally active men.

Methods Recreationally active (n = 5, 37.8 ml.kg.min^-1) and trained (n = 5, 57.9 ml.kg.min^-1) groups were determined according to participants’ VO₂max levels. Firstly, it is collected individual 3-d food records, measured body composition and resting metabolic rate for calculating the daily energy requirements. After that, 3 isocaloric different diet interventions were applied with a weekly interval: normal diet (% 55 carbohydrate,% 15 protein and% 30 fat of daily energy requirement), high carbohydrate diet for one day (% 70 carbohydrate,% 10 protein and% 20 fat of daily energy requirement), and high fat diet for three days (% 20 carbohydrate,% 10 protein and% 70 fat of daily energy requirement). Before each sprint interval session, preprandial resting metabolic rates were measured. Participants had breakfast and following 3 hours- resting period they performed a SIT bout (6 x Wingate anaerobic sprints with a 4.5 min recovery) and immediately after 2 hour-recovery period for evaluating VO₂ and RER. The data were collected from a gas analyzer for 15 min- averages. Energy derived from fat oxidation (as% and gr/min) was calculated using established equations.

Results Basal fat oxidation rate (gr/min) was found statistically high from the other diet modifications, and RER and fat oxidation (%) for 90^th, 105^th and 120^th mins of recovery period after fat rich diet were statistically different when the groups were disregarded. It was found significant differences in RER and fat oxidation (%) for 15 ^th, 90 ^th and 120^th mins of recovery period after fat rich diet in trained group. Additionally, fat oxidation (%) was significantly lower and VO₂ and RER were significantly higher in 15^th min than the other time of recovery period after all diet modifications for all groups.

Conclusions A combination of short-term high-fat diet and sprint interval training is thought to be an alternative way of achieving weight control by increasing fat oxidation from the results of the study.

Acknowledgment This study was supported by the Ege University EBILTEM Scientific Research Foundation [Project Number = 2015-BESYO-02].