We've all heard the advice about the importance of filling our bellies in the morning. It's a notion that's based on a blend of intuition, cultural tradition and science.

Some of the earliest evidence goes back to the 1960s when pioneering researchers in Alameda County, Calif., began documenting the effects of everyday habits. Their long-term study linked eating breakfast — along with a host of other lifestyle choices — to good health and longevity.

And in recent years, the idea of the importance of a morning meal has been bolstered by studies linking breakfast to improved performance in school and a reduced risk of heart disease.

But here's the thing: Lots of American adults aren't sitting down to breakfast anymore. And, it seems, for many of us, eating three "square meals" no longer fits our lifestyle.

As a society, we're moving away from prescribed meal times toward more continuous snacking.

In lieu of breakfast, we may grab a yogurt mid-morning to tide us over. Is that breakfast? Is that a snack? It's hard to say as we make this huge cultural shift towards eating on-the-go.

"The definition of what exactly is a main meal — versus a snack — is starting to blur," Darren Seifer of the research firm NPD Group tells The Salt.

And a recent report from the Food Marketing Institute declared, "Eating culture in the U.S. has promoted snacking to be as culturally prominent as meals."

This trend is most pronounced among millennials. The NPD Group finds that young adults skip twice as many breakfast meals compared to older Americans.

And, increasingly, what millennials are choosing to eat in the morning — when they do make time for it — marks a significant turn in eating habits as well. (Hint: It often isn't cold cereal from a box.)

So, how do we square the "breakfast-is-the-most-important-meal" belief with the shift in our eating habits?

If you sift through the scientific evidence, there doesn't seem to be anything magical about the idea of eating first thing in the morning. Lots of us aren't hungry until a few hours after we wake up. So, if you are a "grab-a-yogurt-at-10 a.m." person, that's OK.

What may be more important for weight management, and even weight loss, is taking in most of your calories before the sun goes down.

A recent study by researchers at Harvard University and the University of Murcia found that dieters who front-loaded their eating to the early part of the day (think: breakfast and a main meal before 3 p.m.) lost more weight than people who ate late into the night.

As we reported, early eaters lost an average of 22 pounds over five months. Late eaters lost much less, an average of 17 pounds.

Our digestive organs aren't as adept at taking in so many calories at night. And sleeping isn't exactly a good way to burn them off. There's even evidence that eating late at night can throw off our body clocks.

And, here's the second bit of advice: What we eat in the morning is likely more important then when we eat.

If your morning meal or snack consists of a bagel or a sweet roll, you not only may be getting a lot of calories, but all those refined carbs and sugar can lead to a spike in blood sugar.

And the result? You may end up feeling hungrier later in the day than if you didn't eat anything at all.

On the other hand, if you eat fiber-rich foods that are high in protein, you're likely to be satisfied for longer. "Non-carbohdrate foods, specifically protein and fat, slow down digestion," says David Ludwig of Boston Children's Hospital.

So, if you are hungry for breakfast in the morning, you might want to take the advice of Drew Ramsey, a psychiatrist at Columbia University and author of The Happiness Diet. As we've reported, he goes for a mix of scrambled eggs, greens and pumpkin seeds.

The body of evidence linking high protein to more satiety is growing. For instance, a new study finds that a high-protein breakfast may help people control their appetites and eat less the remainder of the day.

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