Inc.
Intermittent fasting may not be failing people. They may just be doing it at the wrong time. New research suggests that eating breakfast early and fasting overnight matters more for weight than skipping breakfast and delaying the first meal till the afternoon.
Millions of People Might Be Doing Intermittent Fasting Wrong, According to a Study
Author: Bill Murphy Jr.
According to the International Food Information Council’s 2025 survey, 15 percent of Americans say they are currently doing intermittent fasting — up from 12 percent in 2023.
Every once in a while, I think I ought to have joined them.
I wrote an article here five years ago suggesting it might improve memory — based on a study out of King’s College London — but I still never actually gave it a shot.
As it turns out, it may have been the right call — though probably not for the reasons I would have guessed.
More than 3,000 adults
Researchers at the Barcelona Institute for Global Health tracked more than 7,000 adults between the ages of 40 and 65, collecting data on meal timing, weight, lifestyle habits, and diet.
Five years later, more than 3,000 of those participants came back for follow-up measurements, and the researchers found that two habits were independently linked to lower BMI over that period:
- The first was eating breakfast early in the day.
- The second was extending the overnight fasting window — meaning finishing dinner early and not eating again until morning.
What was not linked to weight benefit: skipping breakfast as a form of intermittent fasting.
Among a subset of men who practiced intermittent fasting specifically by skipping breakfast and eating their first meal after 2 p.m., researchers found no advantage for body weight at all.
That group also tended to have other markers of less healthy living — more smoking, more drinking, less physical activity, and lower adherence to a healthy diet.
“There are different ways of practicing what is known as ‘intermittent fasting,’” explained Camille Lassale, ISGlobal researcher and senior co-author of the study. “What we observed in a subgroup of men who do intermittent fasting by skipping breakfast is that this practice has no effect on body weight.”
Chrononutrition
The researchers place their findings in an emerging field called chrononutrition — the study of not just what you eat, but when, and how meal timing interacts with the body’s internal clock.
The body’s circadian system is built around the rhythms of day and night and the physiological processes that accompany them.
- Eating earlier in the day appears to align better with those rhythms, allowing for better calorie processing and appetite regulation.
- Eating late and skipping breakfast works against that clock, regardless of how long the fasting window technically is.
Thus, a 16-hour fast that runs from 10 p.m. to 2 p.m. the next day may not be doing what people assume.
The same fasting window shifted earlier — finishing dinner at 7 p.m. and eating breakfast at 7 a.m. — appears to be a different thing biologically.
Earlier ISGlobal research connected the same early-eating patterns to lower risk of cardiovascular disease and type 2 diabetes, reinforcing the idea that timing has consequences that extend well beyond weight.
39 million people
The study was conducted entirely in Spain, which has a distinctive meal-timing culture. Dinner is typically eaten much later than in the United States. So, the baseline comparisons may not translate directly.
The research is observational, not a controlled experiment. So, it can’t prove that meal timing caused the differences in weight.
“Recommendations will have to wait for more robust evidence,” said Luciana Pons-Muzzo, one of the study’s lead researchers.
There are roughly 260 million adults in the United States. If the IFIC’s 15 percent figure is right, that works out to somewhere around 39 million people currently doing intermittent fasting.
If even a small portion of them have built their practice around skipping breakfast, this research ought to give them something to think about.
That said, the King’s College study I wrote about five years ago suggested intermittent fasting may have memory benefits that this research doesn’t address.
Maybe I’ll finally give it a try — just not the way most people apparently do it.
Credits: TCA, LLC.