It claimed it could steady a man's nerves and clear his brain.

It could keep you cool in the summer.

It was food for muscles.

For "the warding off of disease."

And for "men of brains."

It was the "most scientific brain and nerve food in existence."

These ads might seem ancient, but in connecting breakfast cereal with health, they aren't so different from how breakfast has been sold to us ever since.

"Cheerios breakfast gives you the power protein."

"How do I stay so slim?"

"I watch what I eat, like Post Grape Nuts for breakfast."

"Data shows women who eat breakfast tend to weigh less than those who don't."

The problem with a lot of these claims is — they're not exactly true.

But the idea of breakfast being good for health—especially weight loss—has persisted for over a century.

So where does this myth come from?

And what does this guy have to do with it?

"For children there's pretty strong evidence that breakfast is a good idea."

That's Julia Belluz who reports on health for Vox.

"As an adult one of the most common claims we hear about breakfast is that it really promotes weight loss."

And that idea didn't come out of nowhere.

There's a whole body of research that connects breakfast with weight loss.

But the methods behind a lot of those studies don't always hold up.

Like this one, that found an association between eating breakfast, and having a low body mass index.

That might be true, but studies like this aren't actually testing what would happen if you were to change your breakfast behavior.

"The problem with those studies is that breakfast skippers and breakfast eaters are different people."

"So maybe the breakfast eaters earn more money and exercise more and that explains why they weigh less than the breakfast skippers."

Most of these studies also don't take into account a major factor: what we eat for breakfast.

There's likely a big difference between eating a bowl of Fruity Pebbles, or a bowl of steel cut oats.

There was even a study of studies that tried to answer the question: does our best research on breakfast prove that it helps with weight loss?

"Researchers looked at 13 randomized controlled trials, the highest quality of evidence on breakfast and its effect on weight loss."

When researchers looked at the studies, they found there's "no evidence to support the notion" that eating breakfast helps you lose weight.

"And they found that breakfast might even had the opposite of the desired effect."

"In some studies people actually gained a little bit of weight when they started to eat breakfast."

So if the available science doesn't actually support this idea, why do we still believe eating breakfast is a healthier way to live?

Well, it has a lot to do with these guys.

Before they got into cereal, Dr. John Harvey Kellogg and his brother Will Keith Kellogg, ran a family business.

The "Battle Creek Sanitarium."

It was a wellness center, a place where the wealthy could go for what they called "biologic living".

It included things like salt glow baths, light treatments, and strange looking exercise machines.

It was there in 1898 that John Harvey came up with corn flakes, as a way to curb indigestion.

But he was also an extremely religious doctor who believed masturbation was a carnal sin.

And he prescribed a bland diet, including corn flakes, as part of the cure.

In 1906, John Harvey's brother, Will Keith, took corn flakes, and mass-marketed them to the world.

By 1917, Good Health, a magazine edited by John Harvey Kellogg, wrote "In many ways, the breakfast is the most important meal of the day."

With claims like this, cereal makers solidified the idea of a healthy breakfast.

"It repairs and it sustains all body tissue."

"It's part of your good breakfast."

And today, a lot of the science cited in cereal commercials has a similar source.

"Part of a good breakfast."

Take a look at the small print on these studies.

This one concludes breakfast skipping is not good for managing weight.

It's funded by the Kellogg Company.

And this one found breakfast skipping had other health costs — like high cholesterol.

It's funded by another major breakfast maker, Quaker Oats.

So, knowing all this about the slippery science of breakfast—should we still be eating it?

There's little evidence that it's a great weight loss strategy, but that doesn't mean breakfast is bad.

"For a lot of people breakfast isn't pointless."

"It can be a good time of day to stock up on vitamins and nutrients."

"But for the rest of us, it's up to you.”

That means, if you're a breakfast eater, like Julia, you can carry on.

And if you're a breakfast-skipper, like me?

Don't worry, the best science we have suggests we're probably just fine either way.

Thanks for watching.