Why Are Scientists So Sure Breakfast Helps You Lose Weight?

Health and medicine explained.
Sept. 9 2013 1:20 PM

Cuckoo for Cocoa Puffs

Why are we so sure that breakfast is the most important meal of the day?

melted butter with maple syrup on pancake
Could eating this really be better for your health than skipping it?

Photo by iStockphoto/Thinkstock

I eat breakfast every morning—usually a bowl of Grape-Nuts with fruit, pecans, and a splash of goat’s-milk yogurt. See how virtuous I am? My dietary habits have been endorsed by the nation’s leading gurus of good health: The Mayo Clinic says that morning meals reduce hunger and stave off obesity; so do Dr. Oz and WebMD, and the editorial page of the New York Times. According to the surgeon general, having a sensible meal to start your day “may be important in achieving and maintaining a healthy weight.” Cheerleading for Cheerios has even made its way into the nation’s highest kitchen—in the Obama household, skipping breakfast is not allowed.

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

The pro-breakfast lobby has only gotten stronger in the past few months. In June researchers at the University of Minnesota published an analysis of 18 years of survey data from 3,600 young adults and showed that people who had breakfast every day gained 4 pounds fewer, on average, than habitual breakfast-skippers. The eaters were also at lower risk for obesity, hypertension, and diabetes. In March another team found similar results among Malaysian adolescents, adding to a long list of cross-cultural confirmations that breakfast is, in fact, the most important meal of the day. The same effect has been studied in Asia and in Europe, in children and in grown-ups, and the answer always seems to be the same: The more regularly you eat breakfast, the slimmer you’ll be.

The mere fact of this association doesn’t tell us very much about what breakfast really does, of course, and it’s possible that the case for eggs and toast has been overblown. A study published last week in the American Journal of Clinical Nutrition starts with this simple fact—that in spite of all these association studies, no one knows exactly what skipping breakfast might be doing to our bodies. The study goes on to make a disturbing claim: Scholars in this field of inquiry—breakfast science—have been fudging facts and misinterpreting the science. The literature shows signs of research bias.

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That doesn’t mean any of the studies described above is fraudulent or dubious. There certainly is a link between skipping meals and getting fat, but Andrew Brown, a nutritionist at the University of Alabama at Birmingham and lead author of the new critique, points out that large surveys of people’s diets and their health are at most suggestive. Lining up several dozen of them in a row doesn’t add much more value to their claims. It could be that my yuppie morning ritual really keeps my BMI in check, perhaps by changing my metabolism or helping to control my appetite. But it’s also possible that my breakfast habits do nothing for me on their own, and that they only correspond to some deeper determinants of health.

As a breakfast-eater, for example, I’m more likely to work out than other people. At least that was the finding of a breakfast study from 2008, which also found that breakfasters tend to be rich and white, and less likely to indulge in cigarettes and alcohol. Any of these factors might protect someone from obesity and diabetes, so it’s hard to know what role might be left to eating breakfast. There are other confounds, too: People with lousy sleeping schedules may have less time for making pancakes. So what makes them fat—missing breakfast or not getting a good night’s rest? Here’s another: People who are trying to lose weight often make a point of missing meals. The fact that they’re on a diet, though, suggests that they’ve been gaining pounds, not shedding them. Does skipping breakfast make them fat, or do people who are getting fat choose to skip breakfast?

Such questions will never get a thorough answer if we’re stuck with the sorts of studies that have been done so far, in which large groups of people are surveyed about their eating habits, then weighed and measured over time. Indeed, Brown and his co-authors in Birmingham show that research on breakfast and obesity has been stagnating in this phase for many years. They considered 58 studies of the question, conducted in 30 countries starting in the early 1990s. Then they pooled the data as it accumulated and plotted the strength of the association between breakfast and obesity as it developed over time. (With each new study published, the link became more certain, since there were more data points in the cumulative analysis.)

According to the paper, the p-value for all this breakfast research put together had dropped below .001 by 1998. That means that given all the studies that had been done by that point, there was just a one-in-1,000 chance that the finding was due to chance—and that breakfast habits are unrelated to body weight. (In general scientists see fit to publish findings if the p-value is less than .05, or one-in-20.) Despite the high degree of certainty, the breakfast scholars kept up their work and published more data on the same question: Does skipping breakfast make you fat? By 2003 this research had zeroed in on the effect of breakfast with such precision that the p-value dropped to .000000000000001. Even so, more studies were done, and then some more again, until the cumulative p-value for this effect sank to less than 10-42. The chances that this was just a random data blip were down to one in 1 tredecillion.

That might make it sound like skipping breakfast causes obesity, and that the government should start passing out free cereal in low-income neighborhoods. But all it really means is that the two are very surely associated in some specific way. For many years scientists have known this to be the case beyond a shadow of a shade of an umbra of a doubt. Yet they’ve continued to replicate the finding instead of doing follow-up work—in the form of randomized, controlled trials—that might extend our knowledge further.

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