Late Night Eating - The Impact on Sleep and Weight Gain
There’s an old saying that “nothing good happens after midnight.” Usually, the old adage is in reference to acts of debauchery, vandalism, and scandal, but a new study notes that eating late doesn’t lead to anything good either.
Presented at ENDO 2019, the Endocrine Society’s annual meeting in New Orleans, LA, the study added to the growing body of literature that has observed a link between a later timing of eating and obesity.
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However, this new study added a new element into the fray -- the effect of late eating and sleep duration.
To assess sleep duration, researchers outfitted 31 overweight and obese test subjects (~age 36 years) with three different types of tracking mechanisms to measure their eating, physical activity, and sleep, including:
- activPAL -- electronic device strapped onto the thigh to track time spent in physical and sedentary activities
- Actiwatch -- wearable tech device that assesses sleep/wake patterns
- MealLogger -- phone app to photograph and timestamp all meals and snack consumed during the day
Researchers tracked the subjects for seven days comparing daily caloric restrictions to time-restricted feeding.
For those of you not aware, time-restricted feeding is a form of intermittent fasting, an eating protocol that only allows for the consumption of food during certain hours of the day. The rest of the day is spent in a fasted state.
At the end of the week-long trial, researchers found that on average, participants consumed food over an 11-hour timeframe during the day, and they slept for an average of seven hours per night.
Additionally, those who tended to eat later in the day fell asleep at a later time, but slept for roughly the same amount of time as those who tended to finish eating earlier in the evening.
Researchers did note that those who tended to eat later had a higher body mass index (BMI) as well as greater body fat.
Co-author of the study, Dr. Adnin Zaman said:
“We used a novel set of methods to show that individuals with overweight or obesity may be eating later into the day. These findings support our overall study, which will look at whether restricting the eating window to earlier on in the day will lower obesity risk. Given that wearable activity monitors and smartphones are now ubiquitous in our modern society, it may soon be possible to consider the timing of behaviors across 24 hours in how we approach the prevention and treatment of obesity.” 
Does Late Eating Really Cause Weight Gain?
One of the oldest nutritional myths is that eating carbs after 6 PM leads to fat gain.
Much of the fear of late night eating stems from some animal research indicating that nighttime eating does indeed result in weight gain, significantly more in fact than if they ate the same amount of calories during the day. 
This research gave rise to the notion that the body uses calories consumed differently based on what time of day they’re ingested and has led to an explosion of time-restricted feeding proponents as well as those promoting the concept of eating according to our circadian rhythm. According to circadian rhythm followers, nighttime is when our bodies are biologically programmed to rest, not process a bunch of calories.
After all, we (like rats) are diurnal creatures, and as such there are fluctuations in glucose tolerance, gastric emptying, and resting energy expenditure throughout the day. 
Some research has even found that the postprandial (after-meal) metabolic response to identical meals changes throughout the day.  Specifically the thermic effect of food is lower at nighttime feedings that if the same meal was consumed earlier in the day. 
Bolstering the anti-late night eating argument are various epidemiological (“associational”) studies noting that individuals consuming a higher proportion of calories later in the day rather than earlier gain weight. 
Remember those, these studies merely show a causal relationship between two things, not a cause and effect.And,, while these studies lend credence to the idea of time-restricted feeding being useful for weight management, not all studies demonstrate a benefit.
In fact, there a number of other associational studies disputing the notion that late night eating leads to weight gain. 
A recent 2017 systematic review concluded that intermittent calorie restrictions offers no significant advantages over restricting calorie intake each day. 
The Bottom Line on Late Night Eating and Weight Gain
Does this latest study show that eating late causes weight gain?
It’s a relatively small trial lasting only a week.
This latest study (as well as the previous epidemiological studies) show an association between late night eaters and a higher BMI.
What we can take from this is that people who tend to eat late are more likely to overeat and exceed their daily caloric needs. It is this excess of calories consumed that is driving weight gain and obesity.
Restricting an individual’s eating window may improve their ability to adhere to a set calorie limit, but there’s nothing magical about consuming your calories only during a few set hours of the day versus spreading them evenly throughout the day in terms of weight loss (provided you stay within your calorie limits).
If defining an “eating window” improves dietary compliance then use time-restricted feeding or intermittent fasting, but if you can eat throughout the day and still maintain your calorie deficit, then there’s no need to abide by some arbitrary feeding window.
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