The causal role of breakfast in energy balance and health: a randomized controlled trial in lean adults. ISRCTN31521726

Background: Popular beliefs that ‘breakfast is the most important meal of the day’ are grounded in cross-sectional observations linking breakfast to health, the causal nature of which remains to be explored under real-life conditions.
Objective: To conduct a randomized controlled trial examining causal links between breakfast habits and all components of energy balance in free-living humans.
Design: The Bath Breakfast Project is a randomized controlled trial with repeated-measures at baseline and follow-up amongst a cohort in South-West England aged 21-60 y with Dual-Energy X-Ray Absorptiometry (DXA)-derived fat mass indices ≤11 kg·m-2 (women; n=21) and ≤7.5 kg·m-2 (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 h) or extended fasting (0 kcal until 1200 h) for 6 weeks, with baseline and follow-up measures of health markers (e.g. hematology/biopsies).
Results: Contrary to popular belief, there was no metabolic adaptation to breakfast (e.g. resting metabolic rate stable within 11 kcal·d-1), with limited subsequent suppression of appetite (energy intake remained 539 kcal·d-1 greater than fasting; 95%CI=157, 920). Rather, physical activity thermogenesis was markedly higher with breakfast than fasting (442 kcal·d-1; 95%CI=34, 851). Body mass and adiposity did not differ between treatments at baseline or follow-up and neither did adipose tissue glucose uptake or systemic indices of cardiovascular health. Twenty-four hour glycemia was more variable during the afternoon/evening with fasting than with breakfast by the final week of intervention (2%; 95%CI=0.1, 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 indices were unaffected by either treatment but breakfast maintained more stable afternoon/evening glycemia than fasting.

背景：‘早餐是一天中最重要的一餐’这一普遍观念基于将早餐与健康相关联的横断面观察，其因果关系的探究尚需在现实生活条件下进一步研究。
目标：本研究旨在通过一项随机对照试验，探讨自由生活的人类中早餐习惯与能量平衡所有组成部分之间的因果关系。
设计：巴思早餐项目是一项随机对照试验，对南英格兰西南部21至60岁的人群（女性n=21，男性n=12，脂肪质量指数≤11 kg·m-2，通过双能X射线吸收测量法得出）进行基线及随访的重复测量。在自由生活条件下，以随机分配的方式，让受试者每日摄入早餐（早餐热量≥700 kcal，于1100 h之前摄入）或延长禁食（0 kcal，直至1200 h）共6周，并在基线和随访期间测量健康指标（例如血液学/活检）。
结果：与普遍观念相反，早餐并未导致代谢适应（例如，基础代谢率在11 kcal·d-1内保持稳定），且后续食欲的抑制有限（能量摄入仍比禁食高出539 kcal·d-1；95%CI=157, 920）。相反，与禁食相比，早餐导致的活动生热显著更高（442 kcal·d-1；95%CI=34, 851）。基线及随访期间，两组受试者的体重和脂肪量、脂肪组织葡萄糖摄取或心血管健康指标均无显著差异。在干预的最后一周，与早餐相比，禁食导致下午/晚上的血糖变化更为显著（2%；95%CI=0.1, 8）。
结论：对于瘦成年人而言，每日早餐与更高的活动生热存在因果关系，整体饮食能量摄入增加，但基础代谢率无变化。两种治疗方法对心血管健康指标均无影响，但早餐比禁食更能维持下午/晚上的血糖稳定。