Fat Oxidation at Rest and During Exercise of Responders and Non-Responders Following a Lifestyle Intervention

Abstract

The inability to oxidize fat is associated with impaired fat loss when undergoing an aerobic exercise intervention. Whether this relationship also applies to a high intensity intermittent exercise (HIIE) lifestyle intervention is undetermined. PURPOSE: The resting respiratory quotient (RQ) and exercise respiratory exchange ratio (RER) of fat loss responders (RES) and non-responders (NRES) to a 12-week lifestyle intervention consisting of HIIE, fish oil (FO) supplementation, and Mediterranean diet (Mediet) were examined. METHODS: Sedentary overweight females (N=34; BMI 27.0 ± 0.5 kg/m2; age 23.5 ± 0.7 yrs) underwent pre- and posttraining testing including a V02peak test, a resting RQ and RER during incremental exercise, a blood draw, and a dual energy x-ray absorptiometry (DEXA) scan to measure body composition. The women (RES; n = 21 and NRES; n = 13) undertook 36 supervised HIIE (8 s:12 s) sessions for a total of 20 minutes. Dietary intake and daily FO (1.7 g of eicosapentaenoic and decosahexaenoic acid) consumption was monitored throughout. The groups were based on body weight loss; RES lost ≥ 1% of their initial body weight while NRES did not. A student's t-tests was used to examine differences pre- and posttraining and between groups. Results are expressed as mean +/- standard error. RESULTS: The RES significantly decreased their fat mass (-2.7 ± 0.4 vs. 0.6 ± 0.4 kg, P<0.001) and overall body weight (-2.8 ± 0.4 vs. 1.2 ± 0.3 kg, P<0.001) compared to NRES. Both groups significantly increased V02peak (0.28 ± 0.03 vs. 0.29 ± 0.03 L/min, P<0.001) and decreased insulin (3.4 ± 1.0 vs. 2.2 ± 0.1 μIU/ml, P<0.05) and interluekin-6 (0.5 ± 0.0 vs. 0.4 ± 0.1 pg/ml, P<0.001) with no significant difference between them. RQ was significantly (P<0.05) higher for NRES (0.93 ± 0.02) than RES (0.87 ± 0.01) and remained unchanged after the intervention. In contrast, RER significantly (P<0.05) decreased during exercise for both groups following the intervention and the reduction was related to fat loss (r=.60, P<0.05). CONCLUSION: Thirty-six bouts of HIIE, FO, and a Mediet led to significant fat loss in most but not all women. The RQ remained unchanged, although significantly different at baseline, whereas the reduction in RER predicted fat loss after the intervention suggesting an increase in fat oxidation during exercise is important for fat loss.