Conventional wisdom is that a calorie is a calorie, no matter when you eat it, and that weight gain is caused by eating more calories than you use. Nutritionists call this the calories in, calories out theory of weight control.
But it might not be as simple as that. New research discovers that what time you eat may play a significant role in gaining weight.
Eating late associated with weight gain
Jun explained that the research team wanted to understand whether late eating actually changes metabolism in a way that promotes obesity.
“So that’s why we set out to do this randomized clinically controlled trial, taking healthy people and make them eat at two different times, control their food, control their diet, and control their sleep times as well,” he said.
Same meals, same sleep time
Jun and team studied 20 healthy volunteers (10 men and 10 women) to find out how their bodies metabolized dinner eaten at 10 p.m. instead of 6 p.m.
All study participants went to sleep at the same time: 11 p.m.
Study findings show that blood sugar levels are higher, and the amount of fat burned lower, when eating a late dinner, even when people ate the same meal.
“We weren’t surprised. Other researchers have done similar work looking at circadian rhythms and diet, and other labs have shown that if you eat out of phase with your body’s normal circadian rhythm, you don’t metabolize glucose the same way,” Jun said.
Not one size fits all
The most interesting part of this study is that researchers found not everyone reacts to eating late meals the same way.
“What surprised me the most was that not everyone was vulnerable in the same way,” said Jun. “There was a group, you know if you looked at the pattern of activity in the preceding 2 weeks, people who were accustomed to sleeping earlier did the worst when we gave them a late meal.”
According to Jun, people that are night owls that ate as late as 2 or 3 a.m. seemed to be unaffected by the change in their meal. “It’s not a one size fits all; there are differences in people’s metabolism that either makes them more vulnerable to late eating or it doesn’t faze them.”
One of the most detailed studies of its kind
Jun pointed out that this study was much more detailed than previous research on the subject. Participants wore activity trackers, had their blood sampled, underwent sleep studies and body fat scans, and ate food containing nonradioactive markers to measure fat metabolism.
“The people got very intensive monitoring performed when they were in the lab. We drew blood every hour, we had their activities and sleep monitored for 2 weeks before they came to the lab,” said Jun. “We gave what’s called a stable isotope tracer, so when they consumed their food we could measure how much of the fat they ate was burned or oxidized.”
Asked if this study provides conclusive proof that it’s when and not necessarily what you eat that can cause weight gain, Jun was confident.
“Yes, I think this at least shows that there’s biological plausibility or biological explanations for how food timing can affect the way your body handles those calories,” he said.
Findings may help guide eating habits
“Although the study was conducted with young adult, healthy weight volunteers, it provides us with some helpful information to guide eating habits,” said Lisa K. Diewald, MS, RD, LDN, program manager, MacDonald Center for Obesity Prevention and Education at Villanova University M. Louise Fitzpatrick College of Nursing.
Diewald adds that the findings are significant for disease prevention.
“This study provides a reminder that cultivating eating habits addressing not only traditional factors such as meal content and size, but also meal timing, may influence the risk of chronic diseases such as diabetes and heart disease down the road.”
According to Diewald, dinner is, by far, the largest meal of the day for most adults in terms of calories.
She explained that busy people typically rush through breakfast and lunch, which often means eating later, and more, than they should. “[This] can leave you yearning for a large meal late at night, which as this study highlights can result in some difficulties with glucose or fat metabolism, even in young individuals with a healthy weight.”
What to do?
Diewald recommended having a small, high protein snack such as Greek yogurt sprinkled with nuts in the late afternoon if you know you’ll be home late.
“Curbing appetite a bit so that if you have to eat later than anticipated, it can be a snack-size meal,” she said.
Choices could include eating a small salad with grilled chicken, half a sandwich and fruit, or a cup of vegetable soup and a glass of low fat milk.
“Aim to eat your largest meal at breakfast or lunch if possible,” said Diewald.
The bottom line
A recent study finds eating a late dinner can cause weight gain and high blood sugar levels regardless of calories.
Researchers found that not everyone reacts the same way, and people who were accustomed to earlier bedtimes had the most weight gain from a late dinner. Night owls were the least affected by a change in mealtime.
According to researchers, this is strong evidence that eating a late meal causes weight gain even if you don’t increase the calories consumed.
Experts say, when working long days it’s a good idea to eat a healthy snack in the afternoon to curb your appetite for a late dinner.
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