When to eat: investigating the role of meal timing and intermittent fasting in body composition and cardiometabolic health in humans

Abstract

Meal timing and intermittent fasting have emerged as potential dietary interventions for managing obesity. However, their impact on human health is still not fully comprehended. The objectives of the present International Doctoral Thesis are to summarize the effects of various types of intermittent fasting on body composition and cardiometabolic health in humans, with a particular emphasis on energy metabolism (Chapter 1). Additionally, the thesis aims to explore the relationship between meal timing with body composition and cardiometabolic risk factors in young men and women (Chapter 4). Furthermore, it seeks to assess the efficacy of three different 8-hour time-restricted eating schedules (early, late and selfselected vs. usual-care) on visceral adipose tissue, body composition and cardiometabolic health in men and women with overweight/obesity and slight metabolic impairments (Chapter 5). The results of this thesis suggest that meal timing is not cross-sectionally associated with body composition in young men and women. However, it was observed that a longer daily eating window and a shorter time from midsleep point to first food intake (i.e., earlier first food intake in a 24-hour cycle) are associated with better cardiometabolic health in young men (Chapter 4). The thesis also highlights that self-selected time-restricted eating (TRE) may be an effective strategy for reducing visceral adipose tissue in men. Additionally, implementing an 8-hour TRE, regardless of the timing of the eating window, as part of a usual-care intervention without specific energy restriction resulted in greater body weight loss in both men and women, although no differences between intervention groups were observed in the changes in body composition or cardiometabolic risk factors. It is noteworthy that weight loss exceeding a clinically meaningful threshold (≥5%) was observed in some individuals, leading to improvements in cardiometabolic health (Chapter 5). Based on the findings of this International Doctoral Thesis, an 8-hour TRE can be considered a simple strategy for clinicians to teach their patients during routine care. It leads to greater body weight loss compared to a usual-care intervention.