Does skipping breakfast make you gain weight?

The question has actually been tested in randomised trials, not just in surveys. In 2019 Sievert and colleagues pooled thirteen randomised controlled trials in the BMJ and found the opposite of what the myth claims. People who ate breakfast weighed slightly more on average, not less. The difference was small, around half a kilo, and the breakfast eaters took in roughly 260 kcal more per day in total. Adding a breakfast was therefore not a good weight-loss strategy, whether or not the person was a habitual breakfast eater.

Dhurandhar and colleagues tested it head-on. 309 adults who wanted to lose weight were randomly assigned to either eat breakfast, skip it, or receive no advice, and were followed for 16 weeks. Even though more than nine in ten followed their instruction, the choice made no difference to weight. All three groups lost about the same small amount.

Betts and colleagues measured why. In their trial the breakfast group took in more energy over the day, but they also moved more, and the rise in spontaneous activity matched the extra calories fairly closely. Metabolism was not slowed by skipping breakfast, and body weight did not differ between the groups.

Taken together, eating or skipping breakfast is neutral for weight in itself. What decides it is the total across the day. An honest caveat: the trials are short and of lower quality than one would like, so this does not mean breakfast is bad, only that it is not the weight-control button it is often made out to be.

The observation behind the myth is true but misleading. In population surveys breakfast eaters often weigh less, but they differ from others in more ways than breakfast alone. They smoke less, move more and eat more regularly otherwise. When you instead compare breakfast against no breakfast with everything else held equal, as the randomised trials do, the effect disappears. On top of that sits a clear incentive. "The most important meal of the day" is at heart a marketing line, and the cereal industry benefits directly from us feeling obliged to eat breakfast. An everyday habit became a health rule because it was repeated often, not because the experiments carried it.

Eat breakfast if you enjoy it and stay fuller from it, and skip it if you would rather spend your calories later in the day. Neither makes you fat in itself. The only thing that counts for weight is the total across the day, not the time on the clock at the first bite. If you skip breakfast, just make sure you don't make up for it at lunch and dinner out of plain hunger. If you want to know which daily intake actually produces weight loss, work out your deficit rather than focusing on individual meals.