Some cereal companies have made a lot of cash off that catchy phrase.

"Many — if not most — studies demonstrating that breakfast eaters are healthier and manage weight better than non-breakfast eaters were sponsored by Kellogg or other breakfast cereal companies whose businesses depend on people believing that breakfast means ready-to-eat cereal," nutrition expert Marion Nestle wrote on her Food Politics blog in 2015. "Independently-funded studies tend to show that any eating pattern can promote health if it provides vegetables and fruits, balances calories, and does not include much junk food."

Nestle keeps her own breakfast advice short and sweet: "If you wake up starving, by all means eat an early breakfast. If not, eat when you are hungry and don't worry about it."

In fact, studies have shown that people who work out in the morning on an empty stomach can burn up to 20% more body fat during their workouts.

Of course, studies still pop up suggesting that skipping breakfast is linked with early death. But personal trainer Max Lowery recently told Insider that such research may not consider every factor.

"People who are more health-conscious overall tend to eat breakfast because they are following health guidelines," Lowery pointed out, "whereas people who skip breakfast are usually unhealthier overall because they are ignoring guidelines"

Still, nutritionists often suggest eating something in the first two to three waking hours of the day to avoid getting cranky and hangry.