In my first year of medical school, I was taught that skipping breakfast is a bad idea for many reasons—notably that it increases hunger later in the day and causes weight gain. This belief has become the accepted wisdom in the medical literature, and is repeated by many doctors, dietitians and nurses, not to mention parents. How many times have you heard that breakfast is "the most important meal of the day"?
But is it true that breakfast skippers tend to gain weight? And if they do put on weight, is avoiding breakfast the cause? I’m interested in these questions from a personal as well as a professional perspective; for my entire adult life I have skipped breakfast (save my double espresso without milk or sugar) and have never had a weight problem. Am I simply an outlier?
A careful analysis of the research on the "proposed effect of breakfast on obesity" (dubbed PEBO), recently published in the American Journal of Clinical Nutrition, has finally provided an answer—of sorts. The authors, from the University of Alabama, focused specifically on the quality of proof and the degree of bias in the research.
They point out that countless observational studies (some sponsored by cereal companies, I should add) have found that skipping breakfast is associated with weight gain. But an association between two things, even if it is demonstrated dozens or hundreds of times, doesn't prove that one causes the other. That is, there may be something else about people who skip breakfast that leads to weight gain (perhaps they tend to have weight problems to begin with, or they exercise less). This can be cleared up only by clinical trials that have habitual breakfast skippers eat breakfast and/or breakfast eaters skip it, and see what happens in the short term, and, more important, in the long term. But there have been remarkably few such trials, and the results have been inconsistent.
Thus, the researchers concluded, the belief that breakfast eating helps with weight control is far stronger than the scientific evidence. That, however, hasn't stopped everyone—from a previous Surgeon General to Dr. Oz—from promoting the notion as fact.
The study authors found many instances where researchers distorted the evidence in ways that supported their belief in the PEBO hypothesis. This is called confirmation bias.
The new analysis does more than challenge this particular belief. It raises similar questions about the validity of much of the conventional wisdom in other scientific areas. In the last few decades we’ve witnessed an important move toward “evidence-based” medicine. Still, humans produce and interpret the evidence, and all of us have biases and blind spots. So it has to be a self-correcting process, helped along by unconventional analyses like this one.