By Michael Ormsbee, PhD, Florida State University

Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily

You’ve probably heard that eating at night is bad for you, but what is the scientific basis for this commonly dispensed advice? Professor Ormsbee explains.

Nighttime Eating Enigmas

If you’re like most people, then you get hungry again before you go to bed at night. For a long time, it was believed that eating late at night before going to sleep was bad for your health and would automatically make you gain body fat.

However, we need to consider several things when the topic of nighttime eating is brought up. According to Professor Ormsbee, you should ask yourself where the recommendations are coming from and what the scientific evidence is. 

Additionally, how is nighttime eating defined? Does this mean you should be monitoring what time you eat dinner? How does the nighttime meal size and composition influence your health? 

“Nighttime feeding has been a major research focus in my lab at Florida State University,” Professor Ormsbee said. “The original premise for starting this line of research stemmed from my glory days as a collegiate ice hockey player. I remember reading about the need to stop eating late at night to avoid gaining fat or feeling lousy.”

Various media experts began to speak up about it, emphasizing that if you want to have a great body composition, you should avoid eating late at night—after dinner—at all costs. 

“The trouble was that I always ate before going to bed,” Professor Ormsbee said. “I thought it would be good to help my body recover from practice and workouts so that I could become a better player. And just about everybody I knew who had low body fat and good muscle mass would not only eat at all times of the day, but would purposefully eat before bed and drink a protein shake or have some kind of protein before going to sleep.”

How could people who ate before bed still have excellent body composition and perform well, when many in the media were telling us the opposite message? As it turns out, several factors influenced this public health message. 

Your Circadian Clock

To understand why most people think that eating at night is bad, we need to dive into some research and physiology. An easy place to start would be with your circadian clock or circadian timing system.

We all have an internal clock that regulates our physiology with our daily behaviors and surrounding environment. For many of us, our typical circadian clock keeps us awake and active during the daytime hours and less active during the evening and night hours. 

Because many of us are less active in the evening and late night hours, our clock is programmed to slow our internal system down at those times, too. However, does a less active system at night translate to fat gained if you eat at night? It depends.

Food we consume has two fates: iIt is either stored for later use or burned for energy. Since our biological clock slows things down at night, it seems obvious that food we eat at night will more likely be stored rather than burned during this time. 

When you eat carbohydrates, the carbohydrates are broken down into smaller components like glucose that enter your blood. In response to the glucose, insulin is secreted from your pancreas to get the glucose into the cells. This effectively lowers blood glucose back to normal.

Glucose and Bedtime Eating

Research shows that for the same amount of glucose, greater amounts of insulin are required to remove it from the blood during the night as compared to the day. More insulin produced equals more storage at night. 

If nighttime eating is not done often, there is likely no problem. However, if it’s repeated over time, chronically high insulin can lead to a desensitization of the insulin receptors and possibly lead to future problems with your glucose control. 

Research has also shown that the energy cost of digesting and processing your food—that is, the thermic effect of food—goes down at night. That means that if you eat the same exact meal for breakfast as you do for dinner, you’ll have a lower energy expenditure in the evening.

We also know that we do not feel as full when we eat foods toward the later part of the day, so there’s a chance we’ll eat more food. Nighttime digestion also takes longer for food eaten later in the day to be emptied from the stomach and into the intestines during this time. 

In summary, when we eat at night, more insulin is needed; we feel less full, so we eat more; and we have a slower digestion and less energy is used to digest and process food. This suggests that our physiology at night favors storage when we eat towards the later part of the day.

This may not be ideal for body composition. Therefore, it is easy to see how the message quickly spread to avoid eating in the evening.

Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.

This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.