Metabolism and Whole-Body Fat Oxidation Following Postexercise Carbohydrate or Protein Intake

This study investigated how postexercise intake of placebo (PLA), protein (PRO), or carbohydrate (CHO) affected fat oxidation (FO) and metabolic parameters during recovery and subsequent exercise.

In a cross-over design, 12 moderately trained women (VO_2max 45 ± 6 ml·min^-1·kg^-1) performed three days of testing. A 23-min control (CON) incremental FO bike test (30-80% VO_2max) was followed by 60 min exercise at 75% VO_2max. Immediately postexercise, subjects ingested PLA, 20 g PRO, or 40 g CHO followed by a second FO bike test 2 h later.

Maximal fat oxidation (MFO) and the intensity at which MFO occurs (Fat_max) increased at the second FO test compared to the first following all three postexercise drinks (MFO for CON = 0.28 ± 0.08, PLA = 0.57 ± 0.13, PRO = 0.52 ± 0.08, CHO = 0.44 ± 0.12 g fat·min^-1; Fat_max for CON = 41 ± 7, PLA = 54 ± 4, PRO = 55 ± 6, CHO = 50 ± 8 %VO_2max, p < 0.01 for all values compared to CON). Resting FO, MFO, and Fat_max were not significantly different between PLA and PRO, but lower for CHO. PRO and CHO increased insulin levels at 1 h postexercise, though both glucose and insulin were equal with PLA at 2 h postexercise. Increased postexercise ketone levels only occurred with PLA.

Protein supplementation immediately postexercise did not affect the doubling in whole body fat oxidation seen during a subsequent exercise trial 2 h later. Neither did it affect resting fat oxidation during the postexercise period despite increased insulin levels and attenuated ketosis. Carbohydrate intake dampened the increase in fat oxidation during the second test, though a significant increase was still observed compared to the first test.