Author(s): HAGANES, K., BAKER, J., MOHOLDT, T., Institution: NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY, Country: NORWAY, Abstract-ID: 1119

INTRODUCTION:
Time-restricted eating (TRE) and high-intensity interval training (HIIT) have emerged as two promising alternatives to the current diet and physical activity recommendations for improving cardiometabolic health. In our previous study, 7 weeks of TRE combined with supervised HIIT (TREHIIT) reduced fat mass, visceral fat, and HbA1c and improved cardiorespiratory fitness (CRF) in women with overweight/obesity (1). The effects of TREHIIT in free-living conditions with minimal follow-up remain unclear. We investigated the effects of a digitally monitored TREHIIT intervention completed outside the laboratory on fat mass and secondary cardiometabolic health outcomes in men and women with overweight/obesity.
METHODS:
We randomized 52 adults (50% female, 37.5 ± 6.9 years, body mass index (BMI) 33.0 ± 4.1 kg/m2) 1:1 to a 7-week TREHIIT intervention or a control group (CON). The intervention included 3 weekly HIIT sessions performed as the participants’ preferred aerobic activity at ≥ 90% maximal heart rate, and a ≤ 10-h/day TRE window with ad libitum energy intake. All HIIT sessions were performed in free-living conditions after one supervised introductory session. Participants in TREHIIT received one weekly follow-up via telephone. Participants in CON received no intervention nor weekly follow-up. The primary outcome was fat mass change. We measured secondary body composition outcomes, CRF, and cardiometabolic health markers in fasting blood samples. We analyzed between-group differences using linear mixed models and considered p <.01 statistically significant for secondary outcomes.
RESULTS:
Forty-two participants completed the study. We found no statistically significant difference in fat mass (-1.0 kg, 95%CI -2.3 to 0.4, p=.146). Participants in TREHIIT had reduced body mass (-2.1 kg, 95%CI -3.4 to -0.8, p=.002) and tendencies of reduced muscle mass (-0.7 kg, 95%CI -1.3 to -0.2, p =.013). CRF, measured as absolute and relative peak oxygen uptake, increased after TREHIIT (0.4 L/min, 95%CI 0.1 to 0.6, p=.008 and 3.4 mL/min/kg, 95%CI: 0.9 to 5.9, p=.010, respectively). There were no statistically significant between-group differences in remaining secondary outcomes.
CONCLUSION:
TREHIIT in a real-world setting with digital follow-up did not reduce fat mass among adults with overweight/obesity. However, CRF significantly increased after TREHIIT, and the improvement was similar to that observed in our previous study of 7 weeks supervised TREHIIT. These findings suggest that a thrice weekly HIIT intervention is feasible without extensive supervision and can induce important improvements in cardiovascular health, but additional support may be required for effective fat mass reduction.

Reference
1. Haganes KL, Silva CP, Eyjólfsdóttir SK, Steen S, Grindberg M, Lydersen S, et al. Time-restricted eating and exercise training improve HbA1c and body composition in women with overweight/obesity: A randomized controlled trial. Cell Metabolism. 2022;34(10):1457-71.e4.