Not for body weight, on the trial evidence. When adults were randomly assigned to eat breakfast or go without, the breakfast groups ate about 260 kcal a day more and did not weigh less; if anything, slightly more3. Breakfast is a fine meal to eat, but the trials do not make it a special one.
The belief is old. The authors of the main review note that breakfast has been called the most important meal of the day in the media since 19173.
Why people believed it
Much of the support came from observational studies, which watch what people already do. In those studies, breakfast eaters tended to weigh less. But breakfast eaters also differ in other ways: they tend to have higher socioeconomic status and other health-related habits, such as a healthier overall diet3. That is called confounding: a third factor, not the breakfast, may explain the link.
Several national dietary guidelines have recommended breakfast for weight management, and the review authors note that most of these recommendations rest on observational findings3.
In plain terms: breakfast eaters were healthier on average, but that does not mean breakfast made them so.
What was studied
A randomised trial settles the chicken-and-egg problem. Chance decides who eats breakfast, so the groups start alike.
The meta-analysis. A 2019 BMJ review pooled 13 randomised trials in adults in high-income countries, mostly the UK and the US3. A meta-analysis combines trials into one estimate.
| What | Number |
|---|---|
| Trials | 13 randomised trials |
| Trials measuring weight | 7 (486 people), mean 7 weeks |
| Trials measuring daily intake | 10 (930 people), mean 2 weeks |
| Quality | mostly low; all at high or unclear risk of bias in at least one area |
Two key single trials. In the Bath Breakfast Project, 33 lean adults were assigned for 6 weeks to a daily breakfast of at least 700 kcal before 11 a.m. or to no food until noon1. Energy intake, resting metabolic rate and physical activity were all measured. In a 16-week trial across several sites, 309 adults with overweight or obesity who were trying to lose weight were told to eat breakfast, told to go without, or given no instruction2.
In plain terms: randomised trials, a few weeks to four months long, in lean adults and adults with extra weight.
What the studies found
Breakfast added energy. In the pooled trials, the breakfast groups took in 259.79 kcal a day more on average (95% confidence interval 78.87 to 440.71)3. A confidence interval is the range the true value most likely sits in. The groups who went without did not fully make up the missing meal later in the day, so their daily total stayed lower. In the Bath trial, breakfast raised intake by 539 kcal a day1.
Breakfast minus no breakfast, daily energy · kcal/day
Breakfast did not lower weight. Across 7 trials, the breakfast groups weighed 0.44 kg more on average (95% CI 0.07 to 0.82) than the groups who went without3. That is a group average over about seven weeks, and the trials disagreed somewhat. In the 16-week trial, the instruction to eat or not eat breakfast made no significant difference to weight, whatever people's habit had been before2. People followed the instruction: self-reported compliance was above 92% in both assigned groups.
Adjusted weight change over 16 weeks, by prior habit and instruction · kg
Told to eat breakfast Told not to
Metabolism did not speed up. Four trials in the review measured metabolic rate, and none found a significant difference3. In the Bath trial, resting metabolic rate stayed within 11 kcal a day1.
Movement changed in lean adults. In the Bath trial, the breakfast group spent 442 kcal a day more on physical activity (95% CI 34 to 851)1. That roughly balanced the extra intake, and body mass and fat did not differ between groups after six weeks. One marker did favour breakfast: by the final week, afternoon and evening blood glucose varied more in the group that went without1. Across the review, total activity energy was not significantly higher in breakfast eaters3.
In plain terms: breakfast adds food, may add movement in some people, and leaves weight about where it was.
What this does and does not mean
The trials do not show that breakfast is bad, or that going without it is a weight-loss tool. The review's authors conclude that adding breakfast "might not be a good strategy for weight loss", and they add that breakfast could have other important effects, such as on concentration in children3. None of the trials studied children.
In nutrition terms, what the trials point to is the day's total. Breakfast is one place to put energy; whether it helps a target depends on what the rest of the day looks like (see calories in, calories out and how many calories to eat).
For people in resistance training, a 2024 crossover trial found that eating breakfast and lunch, or the same food at lunch only, made no clear difference to afternoon squat, bench press and deadlift performance4.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Betts et al., *Am J Clin Nutr*1 | 33 lean adults, 6 weeks | Breakfast: 539 kcal/day more eaten, 442 kcal/day more activity, no change in resting metabolism or body mass; steadier afternoon and evening blood glucose | 2014 |
| Dhurandhar et al., *Am J Clin Nutr*2 | 309 adults with overweight or obesity, 16 weeks | Told to eat or not eat breakfast: no effect on weight change | 2014 |
| Sievert et al., *BMJ*3 | 13 trials in adults | Breakfast groups: about 260 kcal/day more intake; 0.44 kg heavier on average | 2019 |
| Stratton et al., *J Acad Nutr Diet*4 | 39 resistance-trained adults, crossover | No clear change in afternoon lifting performance when total food was similar | 2024 |
Limits worth knowing
- Short trials. Mean follow-up was seven weeks for weight and two weeks for intake3.
- Low quality. All trials in the review were at high or unclear risk of bias in at least one area; people always knew which group they were in3.
- Inconsistent results. The trials varied a lot on intake, less on weight3.
- Adults in rich countries. No children, and no trials from lower-income countries3.
- Abstract only. The three single trials were read as abstracts; the BMJ review in full text.
- Funding. The BMJ review had no specific funding3.
Latest research
The newest study we opened is the 2024 crossover trial in 39 resistance-trained adults, half habitual breakfast eaters and half not4. Each did 4 sets of squat, bench press and deadlift at 80% of their one-rep max in the afternoon, once after breakfast and lunch and once after the same food at lunch only. No difference in reps, bar speed or power was observed, whatever the habit; the authors wrote that meal timing "may not influence" afternoon lifting when total food is similar. It is a single session per condition in young trained adults, not a long-term study.
The short version
- Adults assigned to breakfast ate about 260 kcal a day more in total.
- They did not weigh less; on average, slightly more over a few weeks.
- Breakfast did not change resting metabolism.
- The day's total energy matters more than when the first meal happens.
Educational overview only — not medical advice.
