Time-restricted Feeding Improves Basal Fat Oxidation and Body Composition But Not Fat Oxidation During Exercise

Time-restricted feeding is one of the IF models with significant advantages beyond other IF models, such as simplicity and flexibility, where individuals limit their eating window to specific hours of the day, with a fasting period of at least 12 hours. Ample evidence in humans suggests that prolonged daily cycles of feeding and fasting when aligned with the circadian rhythm, as in the TRF regimen, can alleviate metabolic diseases. Furthermore, research supports a range of health benefits associated with TRF programs in diverse populations, including improvements in body composition and insulin sensitivity, appetite regulation, and achieving a more balanced hunger sensation. Moreover, adopting a 6-hour eating window followed by an 18-hour fasting period can elicit a metabolic shift from relying on glucose to utilizing ketones for energy, which is associated with extended lifespan and a reduced risk of various diseases including type 2 diabetes and obesity. This study aimed to determine the effect of a 6-week TRF on resting and exercise substrate oxidation and changes in blood markers linked to cardiometabolic health.

The aim of this study was to determine the effects of a 6-week TRF program on resting and exercise substrate oxidation, and examine changes in body composition and blood markers linked to cardiometabolic health in recreationally active young males. It was hypothesized that compared to controls, TRF would improve body composition, blood markers associated with cardiometabolic health, and increase substrate oxidation during rest and exercise.

Experimental approach to the problem:

Participants reported to the laboratory on 4 separate occasions. Initially, a familiarization session for V̇O2max testing was conducted on a cycle ergometer. In the second visit, participants repeated V̇O2max test to determine their cardiorespiratory fitness, and this test created the intensity for the submaximal exercise test. A minimum of 48 hours after the V̇O2max test and an overnight fast, body composition, resting metabolic rate (RMR), and substrate oxidation during submaximal exercise were assessed. All measurements were performed between 08:00 a.m. and 12:00 noon in order to eliminate the effect of circadian rhythm. Subsequently, participants were randomly assigned to either TRF or control group. The TRF group received comprehensive nutrition education from a dietitian and was directed to adhere to the 16:8 program for 6 weeks, limiting their eating window to 8 hours daily, while the control group was asked to maintain their eating habits. To assess participant quality of life, the 12-item Short Form Health Survey (SF-12) developed by Ware et al. was administered before and after the 6-week intervention period (38). All participants were asked to maintain their daily physical activity levels throughout the study. A 7-day food diary was completed by all participants at study initiation and during the third and sixth week. After completing the six-week program, all participants underwent post-tests identical to the pre-tests. Venous blood samples were collected from all participants following an overnight fast at baseline and after 6 weeks.

Eligibility Criteria:
Inclusion Criteria:

* Healthy recreationally active males who habitually undergo cycling, running, soccer 2-3 times per week volunteered to participate in this randomized controlled study.

Exclusion Criteria:

* Acute or chronic disease
* Taking any drug or supplements known to affect metabolism
* currently following time-restricted diets
* had lost more than 10% of their weight in the last 3 months before participated the study