Can A Late Dinner Cause Weight Gain? A Look At The Latest Study.
It has always been one of the most common questions I get from people: do you gain more weight if you eat at night? Should we avoid eating after a certain hour if we want to lose or maintain our weight? Does eating after 8pm cause weight gain? Let’s dive into the research to see if eating at night make you gain weight.
Is It Ok To Eat At Night?
While no research has ever definitively tied obesity strictly to the timing of meals, we’ve always been sort of suspicious of how or if our circadian rhythm affects how we metabolize food at different times of the day. We do have a drop in metabolic rate during the night, but I haven’t ever seen this be a proven cause of weight gain. Most often, we see that people who eat late at night eat more overall, eating ultra-processed snack foods, or eating out of boredom or stress and not hunger. Both of these things can cause overeating and subsequent weight gain, irrespective of metabolic rate dips as they sleep.
In other words, the reason why Oprah told people not to eat after 6pm is because that habit cuts total calorie intake overall. Not because you get fatter if you eat late at night. In Spain, people don’t eat dinner until 10pm. Last time I checked, there wasn’t a high rate of obesity in that country, or in any of the European countries where people habitually eat a late dinner.
But I work off of science, not assumptions, and the research just hasn’t been super compelling in terms of proving that eating according to your body clock really makes that much of a difference in a person’s weight, at least not chemically (and here). Sure, we know that people who work shifts are more likely to be overweight, but is that behavioural or chemical?
Burning Fat While Sleeping?
A recent study in the Journal of Clinical Endocrinology and Metabolism, published this month, set out to see if eating a late dinner affects our ability to burn fat while we sleep, potentially increasing the risk of obesity.
The media, predictably, is all over this story. “Eating Before Bedtime Might Pack on the Pounds!” one headline read. ‘For Weight Loss, Don’t Eat Late In The Day,’ said another. Really?
I don’t want to write any spoilers, but both headlines are absurd.
Seriously, any research involving weight and food causes an immediate rise in bullshit media clickbait.
So instead of depending on sensationalist articles, let’s see what the study said.
The Research Behind Weight Gain and Eating Late at Night
Researchers recruited 20 volunteers – 10 men, 10 women, average age 26, average BMI 23. These volunteers typically went to bed at between 11pm – 1pm in their normal lives.
Participants took an MEQ test, which determines if they’re morning or evening people. Seriously, yes. There is a test that figures that out.
Researchers placed participants into two groups. LD (late dinner – 10pm) and RD (routine dinner – 6pm).
Each group went to the lab twice, for two consecutive nights at a time. Their first night was used for acclimation, so no meal was eaten on that night. On the second night, they ate a meal and slept. The late dinner group got dinner at 10pm, and the routine dinner group got their meal at 6pm.
All meals had the same nutritional value.
In their second round lab visit, the groups swapped mealtimes.
The results of the study were interesting. Researchers found:
The late dinner group had elevated glucose and insulin levels for longer, and after 20 hours, it remained a bit higher than the RD group – by 6mg/dl. That’s not very much, FYI.
Post-dinner triglyceride levels were lower, but peaked for longer in the LD group. Funny enough, triglyceride levels for the LD group were lower the next morning. Hint: low triglycerides are a good thing.
Cortisol (a stress hormone) levels after the LD were higher than after the RD, but not significantly.
Fatty acid oxidation (aka ‘fat burning for energy’) was lower in the LD group versus the RD, but not significantly ((74.5 ± 5.7% vs 84.5 ± 5.2%). We do burn fat while we sleep, although the amount isn’t remarkable or large enough to actually lose weight from just, well, sleeping. And these findings echo that.
Free fatty acids – meaning, the amount of fatty acids hanging around in the blood, waiting to be used as energy – were lower in the LD group, but in the end, both groups had comparable levels and the difference was not significant. FYI: High levels of FFA in general are associated with negative health outcomes, such as heart attacks.
What appeared to have a large effect on glucose levels was a person’s MEQ score. ‘Early sleepers,’ who had to go to sleep in the lab at a later hour than normal for them, seemed to have higher glucose levels during the LD phase.
So in short, a late dinner seems to affect us metabolically – glucose and insulin levels may go higher for longer, and we may burn a bit less fat while we sleep. These things may be more pronounced if you typically go to bed early, but are forced to stay up to eat dinner and then go to bed later than normal.
(Can probiotics help with weight loss? Read my Provitalize review here)
But on the flip side, there are other things to consider:
The study was very small and very short. What would be the outcome of the late dinner over the course of years? What were the usual diets and eating times of the volunteers?
It looks as though after 20 hours post-meal, both groups had more or less the same levels of all of the indicators. So while there were differences in the first four hours or so, eventually everyone ended up at the same place.
Each group had one single night of either LD or RD. Is that really enough to base a conclusion on? What else could have happened that may have skewed the results? Remember, these two nights were mere snapshots in time.
65% – 11 vs 7 – of the people in the study, were either morning, unknown, or moderate on their MEQ scores, meaning that these people tended to have earlier bedtimes in their normal lives. And we know that the people who were early sleepers did worse on the metabolic testing than their night-owl counterparts.
So, participants were weighted heavily towards people who a later bedtime may have a greater effect on their glucose and therefore on the study outcome.
And lastly, as far as countries where dinner is typically eaten late, why aren’t more of the residents there, fatter and sicker? It doesn’t make sense, unless there’s a genetic component (Hint: I think there might be.) But still, does eating late – especially if you’re accustomed to it – cause significant metabolic disturbance, leading to weight gain?
Does this mean you gain more weight if you eat at night?
I think we need to consider both the conclusions and the limitations of this study.
Is it possible that eating dinner at 10pm affects our ability to metabolize our meal? Sure. Especially for people who aren’t used to eating and sleeping late. It’s completely plausible that messing with your circadian rhythm and usual schedule that your body is used to, can cause a reaction like we saw with this study.
Overall, the effects of eating late on participants was small and transient, meaning everyone woke up the next day, pretty much the same. That’s all we know right now.
Does this translate into actual, tangible weight gain for the average person?
It might be a reason to think about making crazy changes to your eating and sleeping schedule without acknowledging the possible effects.
But right now, there is absolutely no evidence that a late dinner will ‘pack on the pounds,’ or whatever the media is saying.
Is the sugar in fruit bad for our health? Read this post here.