The latest on eating late at night

Late night eating is associated with weight gain and overeating.

Much of it can be sensibly explained: If your workday begins around 9am, to get enough sleep you’ll likely need to be in bed before midnight, and sleep is a foundation of good health and weight maintenance. Also, very few people chop a salad late in the day – midnight snacks tend to be calorie bombs. 

But there might be more to meal timing than the clustering of less healthy behaviors related to late meals. We have internal clocks in every cell in our body, and those relate to the time of day and the setting of the sun. Eating at certain times might actually affect metabolism and appetite.

A new study in Cell Metabolism goes further into understanding if midnight meals, in and of themselves, increase the risk of gaining weight. In order to do that the researchers, led by Nina Vujovic, kept everything – calorie and composition of meals, light exposure, exercise, sleep schedule etc. – constant. The 16 study participants, who were all overweight or obese, each completed two routines in a laboratory setting, the only difference between the two was that the meal was 250 minutes (~4 hours) later.

The hunger effect

Hunger was assessed by participants’ responses to questions such as how hungry are you right now, how much could you eat right now, and others assessing specific desire to eat starchy, meaty, salty, dairy or veggie foods. Late eating caused increased feelings of hunger.

The researchers measured the appetite regulating hormones leptin (promotes satiety) and ghrelin (promotes hunger). Leptin was decreased in the late eating condition, compared to the early-meal one. 

The metabolic effect

To test how meal timing affects the body’s physiology, the researchers measured body temperature, energy expenditure, and also took blood samples as well as biopsies of fat tissue.

When the participants ate later they burned fewer calories, and the fat cell biopsies showed a tendency to store fat rather than to break it down for energy needs. Late eating caused physiologic and molecular conditions favoring a positive energy balance and weight gain. 

Not just a correlation?

The authors conclude: “Our results show that late eating consistently altered physiological functions and biological processes involved in regulation of energy intake, expenditure, and storage — each of these three in a direction favoring weight gain.”

This small study shows that late eating, by itself, while eating the exact same meal, may tip the scale towards gaining weight. 

In reality, people will likely act on the greater hunger experienced with late meals if they have access to food, which most of us do. 

In reality, this physiologic effect is compounded by behaviors that make late-night eating prone to caloric indiscretion. Chances are that late at night you’d rather order pizza and cookies than chop a salad.

Dr. Ayala