In our ongoing dieting dialogue we spend a lot of time talking about what to eat, but what if we’re leaving out something just as important? What if changing when we eat could significantly improve our health? For the first time, a study offers hard data supporting precisely that argument, showing that eating earlier in the day could affect our health as much as what we’re eating.
Animal studies have found that time-restricted diets can reduce diabetes risk by stabilizing blood sugar. To see if the same holds true for humans, a research team from the University of Alabama at Birmingham (UAB) recruited a group of overweight men, all nearly diabetic, to participate in a controlled 10-week study. Half of the group ate three meals a day within a six-hour period starting around 6:30 am and ending by 3 pm (in effect, they fasted for 18 hours a day). The other half ate three meals during a typical 12-hour day. The groups swapped eating regimens at the end of the first five weeks.
By the end of the study, it was clear that eating within a six-hour window versus a 12-hour window produced three big benefits. First, the participants’ insulin sensitivity increased, resulting in better blood sugar control (insulin is the hormone that keeps blood sugar in check; reduced sensitivity to insulin is a hallmark of prediabetes and diabetes). Their blood pressure also improved as much as if they’d been taking an average dose of blood pressure medication. And their appetite was reduced (a paradoxical outcome considering how many hours a day they weren’t eating, but predictable because their blood sugar had leveled out).
The researchers think that the results come from aligning eating times with natural circadian rhythms.
“If you eat late at night, it’s bad for your metabolism,” said lead study author Courtney Petersen, assistant professor in the UAB Department of Nutrition Sciences. “Our bodies are optimized to do certain things at certain times of the day, and eating in sync with our circadian rhythms seem to improve our health in multiple ways.”
Importantly, the benefits didn’t come from weight loss, because all of the participants ate enough calories to maintain their bodyweight. Rather, the results seemed to come directly from changing when they consumed the same amount of calories.
“Our body’s ability to keep our blood sugar under control is better in the morning than it is in the afternoon and evening,” added Petersen, “so it makes sense to eat most of our food in the morning and early afternoon.”
This was a small study of just eight participants and far from the last word on this topic, but as an initial proof-of-concept, the results are important. As diabetes continues to explode across an increasingly obese population, strategies like shifting eating times to stabilize blood sugar could make a big difference. Same for blood pressure – reducing the amount of medication patients take by changing when they eat is an approach that makes sense.
Having said that, time-restricted diets aren’t easy to follow. Compressing every meal between 6:30 am and 3 pm takes commitment and more than a little willingness to endure stomach grumbles, at least initially before blood sugar spikes level out. We’re accustomed to eating dinner in the 5 – 7 pm window, often followed by a snack or two later at night. Changing that mindset takes work.
Further complicating matters is the growing popularity of fasting diets, mostly unsupported by evidence-based science, but fueled, as all diet fads are, by public demand to conquer our bodies’ worst tendencies. The latest study uses a fasting method (since the participants didn’t eat for 18 hours instead of a typical 10 or 12), but the focus wasn’t on restricting calories via fasting, but rather shifting when they’re eaten.
More research with more participants is needed, no doubt, but these preliminary findings are worth some attention. Food choices matter, but when we consume the food we choose may matter just as much.
The study was published in the journal Cell Metabolism.