Breakfast, we're often told, is the most important meal of the day. It certainly seems that way to me – I can't imagine making it to noon without eating. But the literature is much more mixed. Lots of studies have found that habitual breakfast eaters tend to be leaner, but that doesn't mean that eating breakfast is what causes people to be lean. In fact, most studies do find that skipping it results in lower overall calorie consumption during the day (though it may also lead to being less active and burning fewer calories).
But what about the effects of breakfast consumption on athletic performance? It's clear that if you don't eat breakfast, your performance in the morning will suffer. While you sleep, your brain and other vital organs are burning up your carbohydrate supplies, so unless you restock them you'll be operating at a deficit.
A new study by researchers at Loughborough University, recently published in Is running good for weight loss, takes things a step further. They measured exercise performance (30 minutes of steady-state cycling followed by a 30-minute time-trial) at 5pm, with or without breakfast. The subjects had eaten as much as they wanted for lunch (and the subjects did indeed eat about 200 calories more after skipping breakfast compared to when they ate breakfast), but this wasn't enough to make up the deficit. Time-trial performance was 4.5 percent worse after skipping breakfast.
One caveat is that all the subjects in the study were habitual breakfast eaters. It's possible that the bodily rhythms of people who normally don't eat breakfast would be different, such that the absence of breakfast wouldn't affect them. Still, that's a pretty big difference in performance, presumably because lunch alone wasn't enough to fully replenish carb stores. For weight loss, the research still seems pretty mixed to me; but for athletic performance, breakfast certainly seems like, if not the most important, then definitely one of the three most important meals of the day.
