For people trying to lose weight, it's been hard to miss the tantalizing headlines about the power of consuming meals earlier in the day. It’s not just what you eat, but when you eat it that matters, recent studies seemed to show.
It turns out it’s not quite that simple after all.
The newest research, presented at the American Heart Association’s Scientific Sessions 2020 this month, found obese adults who ate most of their calories by 1 p.m. for three months didn’t lose more weight than those who followed a more typical eating pattern, including eating a big meal after 5 p.m.
The results about time-restricted eating — a form of intermittent fasting — surprised even the authors, who thought they would see a difference between the two groups.
“The bottom line is that how many calories you take in is really much more important than when you eat, and that when you eat probably doesn't impact your weight,” Dr. Nisa Maruthur, the lead author, a primary care physician and associate professor of medicine at Johns Hopkins University in Baltimore, told TODAY.
As for the advice to eat breakfast like a king, lunch like a prince and dinner like a pauper, “I think that if you keep your calories the same, it probably doesn't matter,” she added.
The reason why this study may have had different findings than others — and why it’s particularly compelling — is how controlled it was, standardizing everything except the time of meals. With previous research, it wasn’t clear if people who ate earlier just ate fewer calories, Maruthur noted.
She and her colleagues recruited 41 middle-aged obese adults with pre-diabetes or diabetes. They were then randomly assigned to follow one of two eating patterns for three months:
- Time-restricted eating pattern: Consuming 80% of the day’s calories before 1 p.m.
- Usual feeding pattern: Eating meals at usual times and consuming half of the day’s calories after 5 p.m.
All of the participants ate only the same healthy meals provided by the study’s metabolic kitchen. The calories were precisely controlled so that each person received the amount of food calculated to maintain his or her weight. The only thing that was different was the time of day the participants ate.
Their weight and blood pressure were measured before the start of the study, and then again at four, eight and 12 weeks into it.
After three months, both groups lost weight and had lower blood pressure — results expected when people know their eating habits are being observed and when they eat less salt, as was the case with the provided meals, Maruthur said.
But there was no difference in weight loss or blood pressure between the participants who ate their meals earlier and those who ate on a standard schedule.
Maintain energy balance to maintain weight
With more than 40% of Americans obese, researchers have been interested in time-restricted eating as one strategy to help people control weight. The theory is that the timing of meals matters because the body’s internal clock — the circadian rhythm — does certain things better at different times of the day, better controlling blood sugar and more efficiently digesting food in the morning, for example.
So instead of focusing on what you eat or how much you eat, you channel your focus into the time you eat — keeping it to a small window, said Alexis Wood, an assistant professor at Children's Nutrition Research Center at the Baylor College of Medicine in Houston.
But that doesn't seem to help people in slimming down.
“The overall body of science supports this literature that restricting your feeding window does not affect weight loss or cardiometabolic parameters unless — and here's the caveat — restricting your eating window happens to also change the amount you eat or potentially the type of food you eat,” said Wood, who is also chair of the writing group for the American Heart Association Scientific Statement.
“The biggest thing you can do to help maintain a healthy weight status for yourself… is to maintain energy balance. That is to consume the same calories in as you burn.”
Though time-restricted eating didn’t have an impact on weight loss in this study, Maruthur and her colleagues are still waiting for lab results to see whether it affected how the body handles blood sugar and other hormones. It’s possible there could be some benefits.
Other feeding windows could show different results, she said. Most of the participants in this study, 90%, were female and black, with an average age of 59, but the results would likely also apply to men, and to other races and ages, Maruthur said.
“The number of calories that you take in seems more important than when you eat your calories,” she repeated.