It’s nearly impossible for us not to believe that what we eat has a profound effect on our health. But what we know about the link between food and health is much less than what we believe. A study published this week provides a perfect example.

An overweight person trying to lose weight is likely to hear advice about the importance of eating breakfast. We have some reasons to guess that skipping breakfast might hamper weight loss efforts. Skipping breakfast should increase hunger which might cause overeating at lunch. Hunger can also trigger hormonal changes that make weight loss more difficult. There have even been some observational studies showing that people who eat breakfast are thinner than those who don’t. (See here for a quick primer on the difference between an observational study and a randomized study and why observational studies should be largely ignored.)

Of course in the past we had very good reasons to guess that heavier objects fall faster than lighter objects, that light travels faster going west than north, and that estrogen prevents heart attacks. These guesses were all proven false as soon as someone actually tested them.

In the study published this week, investigators enrolled about 300 overweight and obese adults and randomized them to three groups. One group in addition to receiving general weight loss advice was instructed to eat breakfast every day. The second group was instructed to skip breakfast every day. The third group received general nutrition advice that didn’t mention any advice about breakfast.

The groups were quite compliant with following their instructions. The group that was supposed to skip breakfast almost always did so, and the group that was supposed to eat breakfast almost always did so. The three groups lost equal amounts of weight. The senior investigator of the study, David Allison, summed it up well. “The field of obesity and weight loss is full of commonly held beliefs that have not been subjected to rigorous testing.”

There’s nothing wrong with educated guesses. They’re the seeds of discovery. But without testing we shouldn’t forget that they are not knowledge. We mistakenly keep guesses around for decades, grow comfortable with them, and forget that they’re untested. It seems that the field of nutrition is especially littered with these long-held assumptions. (The myth of the harms of saturated fats is another recent example.) I’m delighted that Dr. Allison is committed to either confirming or discarding them. I hope he gets some help.

Learn more:

Skipping Breakfast May Not Be Bad For Weight Loss After All (Forbes)
Eating breakfast may not matter for weight loss (CNN Health blog)
Passing on Breakfast OK for Weight Loss (Medpage Today)
The effectiveness of breakfast recommendations on weight loss: a randomized controlled trial (The American Journal of Clinical Nutrition)