Fact or Fiction: Is eating late at night unhealthy?

You have probably heard about the importance of eating three meals per day as a part of a healthy diet. Now-a-days, the meaning of a healthy diet varies from person to person. For many people eating three meals a day may not be realistic. Things like culture, work, school, and religion all affect how often we eat. Since the way we eat has changed, there is new research on the most healthful eating habits. A new topic of research is focused on what time you eat instead of how often. This new area of research has left many people wondering what the best time to eat is. This also brings up the question, is eating late at night unhealthy? To answer this question, we will explore the current research to understand how late-night eating affects our health, if at all.

What is “Late-Night” Eating?

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Before we get into the research, I think it is important to explain what is considered “late- night”. “Late-night” eating is any eating that happens during or after the body’s biological “nighttime”. The body’s biological “nighttime” is when our eyes detect the sun going down and signals the release of the hormone melatonin.1 Melatonin is important for the body’s sleep-wake cycle that is a part of what is known as the circadian system. The circadian system is your body’s version of an alarm clock that tells you when to wake up and when to sleep.

The Body’s Internal Clock

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The circadian system is made up of two major “clocks”. The first is the central clock that is found in the part of the brain called the hypothalamus. The second are the peripheral clocks found throughout the body. 2 Together, these “clocks” make up the circadian system. The circadian system is in charge of our sleep-wake cycle, release of hormones, heart health, blood sugar levels, body temperature, and metabolism.2 One of the main roles of the central clock is to detect changes in light which leads to a release of hormones.  On the other hand, the peripheral clocks have specific jobs based on their location. The best way to think of the peripheral clocks is to imagine the different time zones around the world. Each part of the world has its own time zone. The peripheral clocks are the same because each clock is in different organs or tissues in the body. For example, the peripheral clocks found in muscle, fat, and the liver all work to control the body’s ability to lower blood sugar levels by releasing the hormone, insulin. 3 While the central clock is set by light, the peripheral clocks can be reset by food. 4 Any changes to our internal clocks can change the way our circadian system works.  These changes can lead to potential problems in our body. 

Effects of Late-Night Eating

  1. Increased Risk of Obesity

In 2017, a study was done on college students to understand the relationship between the timing of meals and body fat.  For a week, the students were asked to track their meals on an app. The app tracked the time of their meals and measured their portion sizes before and after eating. The students also wore a wristband that tracked their usual schedule. To measure their biological “nighttime”, the students were taken to the lab for a 16-hours. The melatonin in their saliva was checked every hour and when the level stayed above 5pg/ml it was marked as the beginning of their biological “nighttime”. The results found that students with high body fat and a high BMI (body-mass index) ate most of their calories about 1.1 hours closer to their biological “nighttime” than the lean students.5

Another study found that higher intake of calories at least two hours before bed increased the likelihood of being obese by five times. 1

2. Decreased Glucose Tolerance

Recent research has found that both our circadian system and timing of meals influence our body’s ability to release the hormone insulin during high blood sugar levels.6 In 2014, healthy US adults sleep, and wake cycles were monitored for two 8-day periods. During the first three days, the participants were told to sleep from 11pm-7am.  On day four, their sleep schedules were shifted by 12 hours to see how changes to the circadian system would affect glucose tolerance. The results showed that on day one of the study, during the body’s biological “nighttime”, glucose tolerance was 17% lower than during the day.6 Similarly, the study found that the participant’s blood sugar levels two hours after a meal was 8% higher at dinner (at 8pm) than at breakfast (at 8am).6 This suggests that blood sugar control is lower both at night and at biological “nighttime”. One thing to keep in mind is that this study only had 11 participants so more research is needed in this area.

3. Increased Risk of Cardiovascular Disease

Another area of research is the association of late-night eating on the risk for cardiovascular disease. Cardiovascular disease is used to describe diseases that affect both the heart and blood vessels. 7 There are many factors that can increase the risk of heart disease including obesity, saturated fat intake, and cholesterol levels.7 The type of cholesterol that increases the risk of cardiovascular disease is LDL cholesterol which is the “bad” cholesterol. In a study on healthy Taiwanese adults over the age of 19, participant’s timing of food was studied to understand their impact on blood cholesterol levels. The results of the study found that eating 100 calories more at night was associated with a higher risk of higher LDL cholesterol by 0.94mg/dL. 8 Another key finding of the study was that high fat intake at night was associated with a higher value of LDL cholesterol by 2.98mg/dL.8 This study considered night to be anytime between the hours of 8:30pm and 4:59am.

Final Verdict

Now that you know the facts, you may still be wondering, “should I eat at night?” The answer to that question is complicated and depends on a few different things. The frequency, calorie distribution, and quality of food choices related to late-night eating can make the difference to whether it is healthy or unhealthy.  

Frequency

The first question you need to ask yourself is, “how often do I eat at night?” If you usually eat late at night, it might be worth exploring if there are any changes you can make to eat your last meal earlier.  

Calorie Distribution

Another thing to consider is the size of your meals at night. The more calories you eat closer to bedtime, the less time you have to use it in the  form of energy.  This can increase the amount of food that is converted and stored as fat.  Therefore, eating most of your calories earlier in the day can help to prevent this from happening. 

Quality of Food Choices

You should also take some time to think about what kinds of foods you eat before bed. Most of the time when we roam into the kitchen late at night, we are after foods that are sweet, salty, or maybe both. Large meals that contain a large amount of carbohydrate can give you a boost of energy that can make it hard to fall asleep. Similarly, foods that are high in added sugar can give you a “sugar” rush that can leave you tossing and turning all night. Thinking about the food you usually eat late at night may help to give you a better idea of whether your late-night eating habits are healthy or not.

Regardless of the time of day, poor food choices are still poor food choices.

Depending on your usual habits, eating late at night can either be healthy or unhealthy.  Keep in mind that nutrition is not a one size fits all. Things like genetics, environment, age, race/ethnicity can make a difference in our risk for certain conditions/diseases. While some of the research suggests that regular late-night eating may increase the risk of obesity, poor blood sugar control, and cardiovascular disease more research is needed.  

For now, all you need to know is that the choices you make matter day or night.

Tips for Late-Night Eating

1. Choose foods that are high in fiber

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To avoid eating large portions before bed, choose foods like fruits and vegetables that are high in fiber but low in calories. The fiber will help to fill you up without overdoing it on the portion sizes.

2. Pair your carbohydrates with a source of fat

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Another way to fill up without eating large portions is to pair a source of carbohydrates like fruits or vegetables with a source of fat like peanut butter. Fat just like fiber works to fill you up with less. By pairing the two together, you can have a satisfying meal or snack that will keep you from eating larger portions.

3. Drink some water before bed

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The part of our brain that signals hunger is the same part that signals thirst. The hypothalamus controls both hunger and thirst so it is common to confuse the two.  Before you make your way to the kitchen for a snack or meal, try drinking some water first. You might find that is what you really needed.

4. Avoid processed foods

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Many of the studies that mentioned negative effects of eating late at night also mentioned eating high calorie foods late at night. The most common sources of high calories are processed and refined foods like desserts, pastries, and frozen meals. Instead of these foods choose whole grains, fruits, vegetables, healthy fats, and lean protein.

References:

1. Lopez-Minguez J, Gómez-Abellán P, Garaulet M. Timing of Breakfast, Lunch, and Dinner. Effects on Obesity and Metabolic Risk. Nutrients. 2019;11(11):2624. Published 2019 Nov 1. doi:10.3390/nu11112624

2. Serin Y, Acar Tek N. Effect of Circadian Rhythm on Metabolic Processes and the Regulation of Energy Balance. Ann Nutr Metab. 2019;74(4):322-330. doi:10.1159/000500071

3. Stenvers DJ, Scheer FAJL, Schrauwen P, la Fleur SE, Kalsbeek A. Circadian clocks and insulin resistance. Nat Rev Endocrinol. 2019;15(2):75-89. doi:10.1038/s41574-018-0122-1

4. Challet E. The circadian regulation of food intake. Nat Rev Endocrinol. 2019;15(7):393-405. doi:10.1038/s41574-019-0210-x

5. McHill AW, Phillips AJ, Czeisler CA, et al. Later circadian timing of food intake is associated with increased body fat. Am J Clin Nutr. 2017;106(5):1213-1219. doi:10.3945/ajcn.117.161588

6. Morris CJ, Yang JN, Garcia JI, et al. Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans. Proc Natl Acad Sci U S A. 2015;112(17):E2225-E2234. doi:10.1073/pnas.1418955112

7. St-Onge MP, Ard J, Baskin ML, et al. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation. 2017;135(9):e96-e121. doi:10.1161/CIR.0000000000000476

8. Chen HJ, Chuang SY, Chang HY, Pan WH. Energy intake at different times of the day: Its association with elevated total and LDL cholesterol levels. Nutr Metab Cardiovasc Dis. 2019;29(4):390-397. doi:10.1016/j.numecd.2019.01.003

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