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Breakfast is widely touted as not only the most important meal of the day in general, but specifically in relation to weight loss. This is not just a pop culture prescription from checkout aisle magazines, but an idea put forward by prestigious institutions such as Johns Hopkins, NYU, and the Mayo Clinic. Even the United States Surgeon General. “Want to trim your waist?” read a headline from the American Dietetic Association. “Try eating breakfast!”—referring to breakfast as perhaps the “best kept waist-trimming secret.” But is it true? The Duke School of Medicine’s health newsletter was skeptical: “It’s always been billed as the most important meal of the day—until now.”

While it is widely presumed that eating breakfast protects against obesity, the belief is held up as a poster child of biased distortion of the scientific record. No one can argue that there isn’t an association between body weight and breakfast. Studies have shown that obesity and breakfast skipping tend to go together beyond a shadow of a doubt, in fact, gratuitously so.

By 1998, we already had what might be considered strong evidence of an association between breakfast skipping and obesity, but researchers continued to repeat such studies to the point of ridiculousness. This meta-analysis found that by 2011, the combined P value had reached 10-42. Okay, what does that mean? Why is that ridiculous? In science, “P value” refers to the chance of getting a result that extreme if in fact there really was no such effect. How small a chance is 10-42? This is how small that number is.

In other words, the probability that the association found between obesity and breakfast skipping was just a fluke is less than the chances of winning the lottery not once, but five times in a row, and then, subsequently getting struck and killed by lightning. Okay, so the association between breakfast skipping and obesity is indeed beyond question. We know that that association is true. People who skip breakfast are more likely to be overweight—that’s true beyond a shadow of a doubt. The question, though, is whether that iron-clad relationship between breakfast skipping and obesity is actually cause-and-effect.

To illustrate the difference between correlation and causation, let me share an example of the manipulation of science by the candy industry. The National Confectioner’s Association had the gall to warn parents that restricting candy may make their children fat. They justify this outlandish claim with this study (that they funded, of course) that showed that candy-consuming children and adolescents were significantly less likely to be overweight and obese. The industry-funded researchers go on to imply that this exonerates candy. But what’s more likely? That cutting down on candy led to obesity, or rather that obesity led to cutting down on candy? In other words, the lower candy consumption may reflect the consequences of obesity, not the cause, as parents of obese children try to restrict treats.

Similarly, the finding that those who skip breakfast tend to be heavier is equivalent to saying those who are heavier tend to skip breakfast. Doesn’t it seem more likely that overweight individuals might just be skipping breakfast in an effort to eat less, rather than eating fewer meals somehow leading to weight gain? Now it’s possible that skipping breakfast could slow your metabolism or cause you to overeat so much later in the day that you’d gain weight, but you can’t know for sure until you put it to the test.

Sometimes, randomized controlled trials are infeasible, impossible, or unethical. To test to see if parachutes save lives, you can’t exactly boot half the people off a plane without them. But you could easily randomize people to eat breakfast or not, to see what happens. And, it turns out eating breakfast does not seem to affect your metabolic rate or sufficiently suppress your appetite. Most studies—95 percent—found that eating breakfast leads to the same or greater calorie intake over the day. Even when people ate more at lunch after skipping breakfast, they didn’t tend to eat an entire breakfast worth of calories more, and so ended up eating fewer calories overall. For example, feed people about a 500-calorie breakfast, and at lunch they may eat about 150 calories less than those randomized to skip breakfast, but they would still end up with about a 350-calorie surplus over the breakfast skippers. Does this then translate into weight gain over time?

Researchers at Brigham Young University randomized 49 women who habitually skipped breakfast to either start eating breakfast or continue skipping. If breakfast somehow magically leads to weight loss, then the newly eating breakfast group should benefit. But no, compared to those who continued to skip breakfast, adding the extra meal led to hundreds more daily calories consumed, and nearly a half pound of weight gain a week.

If you already eat breakfast and start skipping it, will you lose weight? We’ll find out, next.

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