title: The causal role of breakfast in energy balance and health: a randomized controlled trial in lean adults.
abstract: BACKGROUND
  Popular beliefs that breakfast is the most important meal of the day are grounded in cross-sectional observations that link breakfast to health, the causal nature of which remains to be explored under real-life conditions.
  
  
  OBJECTIVE
  The aim was to conduct a randomized controlled trial examining causal links between breakfast habits and all components of energy balance in free-living humans.
  
  
  METHODS
  The Bath Breakfast Project is a randomized controlled trial with repeated-measures at baseline and follow-up in a cohort in southwest England aged 21-60 y with dual-energy X-ray absorptiometry-derived fat mass indexes ≤11 kg/m² in women (n = 21) and ≤7.5 kg/m² in men (n = 12). Components of energy balance (resting metabolic rate, physical activity thermogenesis, energy intake) and 24-h glycemic responses were measured under free-living conditions with random allocation to daily breakfast (≥700 kcal before 1100) or extended fasting (0 kcal until 1200) for 6 wk, with baseline and follow-up measures of health markers (eg, hematology/biopsies).
  
  
  RESULTS
  Contrary to popular belief, there was no metabolic adaptation to breakfast (eg, resting metabolic rate stable within 11 kcal/d), with limited subsequent suppression of appetite (energy intake remained 539 kcal/d greater than after fasting; 95% CI: 157, 920 kcal/d). Rather, physical activity thermogenesis was markedly higher with breakfast than with fasting (442 kcal/d; 95% CI: 34, 851 kcal/d). Body mass and adiposity did not differ between treatments at baseline or follow-up and neither did adipose tissue glucose uptake or systemic indexes of cardiovascular health. Continuously measured glycemia was more variable during the afternoon and evening with fasting than with breakfast by the final week of the intervention (CV: 3.9%; 95% CI: 0.1%, 7.8%).
  
  
  CONCLUSIONS
  Daily breakfast is causally linked to higher physical activity thermogenesis in lean adults, with greater overall dietary energy intake but no change in resting metabolism. Cardiovascular health indexes were unaffected by either of the treatments, but breakfast maintained more stable afternoon and evening glycemia than did fasting.
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: James A
authors.initials: JA
authors.lastname: Betts
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: Judith D
authors.initials: JD
authors.lastname: Richardson
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: Enhad A
authors.initials: EA
authors.lastname: Chowdhury
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: Geoffrey D
authors.initials: GD
authors.lastname: Holman
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: Kostas
authors.initials: K
authors.lastname: Tsintzas
authors.affiliation: From the Departments for Health (JAB, JDR, EAC, and DT) and Biology and Biochemistry (GDH), University of Bath, Bath, United Kingdom; and the School of Life Sciences, Queen's Medical Centre, Nottingham, United Kingdom (KT).
authors.forename: Dylan
authors.initials: D
authors.lastname: Thompson
mesh_terms: D000328:Adult; D001069:Appetite Regulation; D015415:Biomarkers / Q000097:blood; D001786:Blood Glucose / Q000032:analysis; D062408:Breakfast; D015331:Cohort Studies; D002149:Energy Intake; D004734:Energy Metabolism; D005247:Feeding Behavior; D005260:Female; D005500:Follow-Up Studies; D006293:Health Promotion; D006801:Humans; D006943:Hyperglycemia / Q000097:blood / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D022722:Thermogenesis; D015854:Up-Regulation; D055815:Young Adult
chemical_list: D015415:Biomarkers; D001786:Blood Glucose