Breakfast is essential

The claim, as heard: "Breakfast is the most important meal — skip it and your metabolism slows and you overeat later."

What the data show. The claim comes from observation: people who eat breakfast tend to weigh less. People who eat breakfast also tend to sleep more regularly, smoke less, drink less and exercise more, which is the problem with observation. When the question was put to randomised trials — assigning people to eat or skip breakfast — a systematic review and meta-analysis of thirteen of them found that breakfast eaters ate somewhat more over the day, and that skipping breakfast produced a small weight difference in favour of skipping, or none. The trials are short and mostly of low quality, so the review's conclusion is deliberately modest: breakfast is not a tool for weight loss, and there is no evidence that skipping it causes weight gain. It does not say "skip breakfast"; it says the meal is neutral.

Verdict: false as a weight claim. Evidence grade B, from a meta-analysis of short, low-quality trials that nevertheless agree in direction.

The grain of truth. For people who are hungry in the morning, breakfast is where a good share of the day's protein and fibre can go, and a regular pattern helps some people avoid the late-evening eating that does add up. Whether the pattern includes breakfast is a matter of preference, not physiology.

One sentence to remember: eat breakfast if you like it; it is neither required nor forbidden, and it does not change what a deficit does.