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.Design: 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. This trial was registered at www.isrctn.org as ISRCTN31521726.

The effect of breakfast on appetite regulation, energy balance and exercise performance

“…A number of intervention studies have investigated breakfast omission over longer periods of time, often using food records to estimate daily energy intake ( Table 2). Whilst the results of these studies are slightly more varied, once again the weight of evidence suggests that omission of breakfast in the morning will reduce daily energy intake in the longer term (14,37,41) . In one of these studies, a reduction in energy intake was observed in a 6 week between groups breakfast intervention study.…”

“…after 12·00 hours were unaffected by consumption or omission of breakfast in the morning, resulting in a reduced energy intake of approximately 2300 kJ/d when breakfast was omitted (37) . In contrast to this, Halsey et al (42) found no difference in daily energy intake, independent of consumption or omission of an ad libitum breakfast.…”

“…It is interesting to note that some of the aforementioned longer term breakfast intervention studies have failed to observe a reduction in body weight (37,45) , despite observing reductions in energy intake when breakfast is omitted. This may be due to underreporting of energy intake as opposed to a genuine reduction (20) , but also could suggest an interaction between breakfast and energy expenditure.…”

“…Further research is required to determine the long-term effect of breakfast on the hormonal regulation of appetite. This has been partly addressed, with one study finding impaired post-prandial insulin sensitivity after 2 weeks of breakfast omission (36) and another finding no change in fasted insulin sensitivity as well as no difference in fasted acylated ghrelin, PYY, GLP-1 or leptin after 6 weeks of either consuming or omitting breakfast (37) .…”

Effect of breakfast omission: Constrained to morning?

“…Whilst observational studies are useful for establishing a potential link between a behavior and an outcome, randomized controlled trials are essential in order to make definitive causal statements. More recent studies using free-living designs over periods of weeks and months [5][6][7][8], combined with evidence from more tightly-controlled laboratory studies conducted within a single day [9][10][11] are beginning to address the causality of breakfast consumption, body weight regulation and health, whilst providing mechanistic insight into any causal effects.…”