Breakfast is not the most important meal for weight. The trials point the other way.
Pooling 13 randomised trials, people assigned to eat breakfast ended up 0.44 kg heavier and ate 260 more calories a day than people assigned to skip it. The trials were small, short and mostly low quality.
Adding breakfast is not an effective weight-loss strategy, and in randomised trials it points mildly the wrong way. A BMJ meta-analysis of 13 trials in high-income countries found a small weight difference favouring the people told to skip breakfast — 0.44 kg, 95% confidence interval 0.07 to 0.82 — and a higher total daily energy intake among those assigned to eat it, by 259.79 kcal a day (78.87 to 440.71) [s1]. The evidence behind both numbers is weak enough that the review's own conclusion is a caution rather than a recommendation, and the honest answer to "is breakfast the most important meal of the day?" is that for body weight, no trial supports the claim.
Why the observational picture points the other way
Breakfast eating is reliably associated with lower body weight in cross-sectional and cohort data [s2]. That association is the basis for the public-health advice, and it is also exactly the kind of finding that randomisation exists to test — because people who eat breakfast differ from people who do not in sleep, shift work, smoking, income, alcohol use and a dozen other things that also track weight.
The BMJ review restricted itself to randomised controlled trials in adults from high-income countries comparing breakfast consumption with no breakfast consumption, searching PubMed, Ovid Medline and CINAHL for trials published between January 1990 and January 2018, plus trial registries in October 2018 for unpublished or ongoing work [s1]. Thirteen trials met criteria: seven measuring weight change, ten measuring energy intake [s1].
The result, and how fragile it is
Neither pooled estimate is large, and both carry serious caveats the review states plainly. The 0.44 kg weight difference came with some inconsistency across trials (I² = 43%) [s1]. The 259.79 kcal energy-intake difference came with substantial inconsistency (I² = 80%) [s1]. Every included trial was at high or unclear risk of bias in at least one domain, and all had short follow-up — averaging seven weeks for weight and two weeks for energy intake [s1]. The reviewers describe the quality of included studies as mostly low and say the findings should be interpreted with caution [s1].
Their conclusion is worth reading as written: the addition of breakfast might not be a good strategy for weight loss regardless of established breakfast habit, and caution is needed when recommending breakfast for weight loss in adults, as it could have the opposite effect [s1].
The single largest trial
The best individual test was run in the US in 2014. A multisite, 16-week, three-arm randomised trial enrolled 309 otherwise healthy adults aged 20 to 65 with a body mass index between 25 and 40 who were trying to lose weight, randomising them to a control group, a group told to eat breakfast, or a group told to skip it, with randomisation stratified by pre-existing breakfast habit [s2]. Two hundred and eighty-three completed the intervention [s2].
Treatment assignment had no significant effect on weight loss, and there was no interaction between a participant's baseline breakfast habit and their assigned instruction [s2]. Among habitual skippers, adjusted weight changes were −0.71, −0.76 and −0.61 kg for control, breakfast and no-breakfast groups respectively; among habitual breakfast eaters, −0.53, −0.59 and −0.71 kg [s2]. Compliance was high — 93.6% in the breakfast group and 92.4% in the no-breakfast group by self-report — so the null result is not obviously an adherence failure [s2]. The authors' phrasing: contrary to widely espoused views, this had no discernable effect on weight loss in free-living adults who were attempting to lose weight [s2].
What "breakfast" meant in these studies
Neither paper defines breakfast by content, and both define it by instruction. The BMJ review's inclusion criterion was trials in adults from high-income countries comparing breakfast consumption with no breakfast consumption that reported body weight or energy intake [s1]. The 2014 trial randomised people to a recommendation — to eat breakfast, to skip it, or to a control group — and then measured whether they followed it and what happened to their weight [s2]. That design tests the public-health advice as it is actually delivered, which is a recommendation rather than a supervised feeding protocol, and it is arguably the more relevant question. It is also the design least able to detect an effect of a specific breakfast composition, because there wasn't one.
The 2014 trial's stratification is the detail that closes off the most common rescue argument. It randomised separately within habitual breakfast eaters and habitual skippers, precisely to test whether the advice works for people whose existing habit it contradicts [s2]. It did not: there was no interaction between initial breakfast-eating status and treatment assignment [s2].
What the trials do not answer
Almost everything except weight. These studies measured body weight and energy intake over weeks, not cardiometabolic markers, cognitive performance, school or work outcomes, or anything over years [s1] [s2]. They were conducted in adults in high-income countries [s1]; children, whose breakfast literature is separate and largely about school performance, are outside their scope entirely. They compared eating breakfast with skipping it, and say nothing about what is eaten at either meal. And they cannot address people with diabetes, disordered eating, or medication schedules tied to food, none of whom were the study populations.
The 0.44 kg figure is also not a reason to skip breakfast. It is a two-month average difference in short trials of mostly low quality [s1], and the larger single trial found nothing at all in either direction [s2]. The defensible reading is that the meal appears not to matter much for weight in either direction, which is a considerably duller finding than the slogan it displaces.
This article is informational and is not medical advice.
Sources
- Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials — The BMJ, 2019-01-30
- The effectiveness of breakfast recommendations on weight loss: a randomized controlled trial — The American Journal of Clinical Nutrition, 2014
Sources
- Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials — The BMJ , January 30, 2019
- The effectiveness of breakfast recommendations on weight loss: a randomized controlled trial — The American Journal of Clinical Nutrition , June 5, 2014
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