Breakfast is the most important meal of the day
Not wrong, but our understanding became significantly more precise.
TaughtNever skip breakfast. It kick-starts your metabolism and skipping it makes you gain weight.
NowThe evidence is much weaker than the slogan. Randomized trials, including a 2014 study in the American Journal of Clinical Nutrition, found no significant weight effect from eating or skipping breakfast, and much of the supporting research was observational or industry-funded.
What actually happened
The phrase itself was popularized in the early twentieth century in cereal advertising, which is not a reason it is false but is a reason to check the evidence carefully.
Most of the support was observational: people who eat breakfast tend to weigh less. But breakfast-eaters also smoke less, exercise more, and drink less, so the correlation says little about cause. When Emily Dhurandhar's team ran a proper randomized controlled trial in 2014, assigning people to eat or skip breakfast, they found no significant difference in weight loss. A 2019 BMJ meta-analysis reached similar conclusions and found breakfast eaters actually consumed slightly more total daily calories. Two honest caveats: children are a different case, with reasonable evidence that breakfast helps school performance, especially for those who are food insecure. And regular eaters who suddenly skip may simply overeat later. The claim is not so much wrong as vastly oversold.
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Who was taught this
Still standard through 2015, so anyone who finished school between 1950 and 2014 learned the earlier version.