Does Eating Late at Night Really Make You Fat? (chrono-nutrition)


  1. It is natural to gain weight from eating at night
  2. When late night eating habits lead to weight gain
  3. It's impossible to explain weight gain with BMAL1
  4. Thin people would rather lose weight
    The bottom line

In Japan, many people (especially women) tend to avoid eating dinner, a dessert or sweets late at night (after nine p.m.) because they do not want to gain weight.

But does that really make sense? Actually, some people say that they have started eating dinner late at night and gained more weight than before, but I believe that is a misconception.

1. In a sense, it is natural to gain weight from eating at night

While we sleep at night, our bodies are not resting. They are doing something very important for us. Although the mechanism may not be entirely understood, sleep is an important time for not only organizing and consolidating memories in the brain, but also for repairing and regenerating damaged tissues to prepare for the next day's activities. 

In particular, after sleep, the body secretes more growth hormone, which stimulate metabolism, thereby repairing damaged cells throughout the body, recovering from fatigue, and enhancing immune function. And, the synthesis of protein and fats is promoted.

Thus, in a sense, isn't it natural that eating at night tends to make everyone gain weight than in the morning or afternoon?

If you are on a diet regularly or a person who is trying to cut back on calories, you may gain a few kilograms overnight if you eat more calories than you need and go to bed.

However, that is the case when your present weight goes back to your base weight (see Figure-1), and regarding this, it doesn’t matter whether the meal was eaten at seven or ten p.m.

base weight


2. When late night eating habits lead to weight gain

On the other hand, I sometimes hear that people did not gain weight when they were eating dinner around seven p.m., but gradually gained weight over time after working overtime and eating late at night.  But that is a separate issue from [1] above, and it can be explained by the fact of one’s base weight itself going up in my intestinal starvation theory. 

First of all, many people tend to skip breakfast if dinner is served late at night. This means, in most cases, they only have two meals a day, lunch and dinner.

unbalanced lunch

If you eat an unbalanced meal leaning toward carbohydrates and some protein such as ramen, curry rice, or hamburgers for lunch (quantity is not the issue), that is the only meal you have in your stomach since you have not eaten breakfast.

If you don't eat anything until nine or ten p.m., there is a possibility that intestinal starvation will be induced little by little.

And in this case, eating late at night is not a "cause" of weight gain, but a "consequence." The cause for this is an unbalanced diet skewed towards carbohydrates and digestible protein, and putting up with hunger over many  hours between meals.

One way to prevent this is to eat a well-balanced meal both at lunch and dinner. And if dinner is going to be late, you can diversify meals by snacking on sandwiches, cookies, milk, etc. around five p.m.

(Balanced lunch box)

3. It is impossible to explain weight gain with BMAL1

In Japan, many experts confuse the two meanings of [1] and [2], and explain them as if the secretion volume of BMAL1(Brain and muscle Arnt-like protein-1 ) and weight gain are correlated.

BMAL1 is a protein involved in the body's circadian rhythms, and is said to be related to adipogenesis.
Its secretion begins to increase around six p.m. and peaks between ten p.m. and two a.m., which seems to be thought as a rationale behind the fact that people are several times more likely to gain weight if they eat late at night(e.g. ten p.m.) than eating at six p.m. for the same number of calories. 

However, I think that explanation is a bit of a stretch. The reason is that the "digestion time" is missing. 

For example, if they eat a meal at ten p.m., it will take four to six hours for it to be digested and absorbed, depending on the person and how foods are combined, etc . Fats/oils are particularly indigestible, so they may find that even in the morning after seven to eight hours, their food is still undigested and their stomach is upset.

In other words, if it is not digested, it cannot be absorbed, so there is no way to correlate the meal time with the BMAL1 value.

The reason why BMAL1 peaks between ten p.m. and two a.m. is that if we humans have been eating dinner around six p.m. since ancient times, I suspect that BMAL1 levels are also higher so that lipids can be successfully synthesized just as the food is digested and absorbed and fatty acids are transported to all cells in the body.

4. Thin people would rather lose weight

If people eat breakfast, lunch, and dinner properly, I believe, for most of them, eating before bed does not cause much weight gain.

As I said earlier, if a person who normally moderates their caloric intake eats sweets or ramen late at night, they may gain a few kilograms, but it means their present weight goes back to their base weight and should stop at a certain weight. (This should be easily proven by research.)

Also, In Japan, it is said that there are many thin people who have weak stomachs or droopy stomachs (gastroptosis), and even if they eat dessert, sweets or a light meal before bedtime in addition to their three meals in order to gain weight, it is more likely that they will not gain weight. In fact, I suppose that they may even lose weight (at least to me, this is one hundred percent true).

The reason being that, by nature, it is good to rest your body and your stomach while you sleep, but if you eat before going to bed, your gastrointestinal tract has to continue to work throughout the night.
I suspect that this may result in decreased cellular regeneration and the decreased synthesis of protein and lipids. 

The bottome line

(1) In relation to hormones secreted, protein and lipid synthesis may occur more during sleep, so in a sense, everyone should be more likely to gain weight with dinner than in the daytime. Especially those who usually eat fewer calories because of dieting will gain a few kilos if they eat more calories than necessary at night. But in this case it doesn't matter whether they eat at seven p.m. or ten p.m.

(2) In terms of my intestinal starvation theory, late-night eating habits can lead to an increase in weight. Those people tend to skip breakfast and eat two meals a day. If they eat a carbohydrate-rich, unbalanced meal for lunch and hold off until a late dinner, it can lead to inducing intestinal starvation and an increase in base weight over time.

(3) I believe it is unreasonable to correlate the secretion volume of BMAL1-a protein involved in the body's circadian rhythms-which is related to adipogenesis, with meal time, and that say that, “late night eating makes people gain weight.” This is because the time required for digestion and absorption is not taken into account.

(4) For some thin people who want to gain weight, eating a high-calorie meal or a sweet before bed in addition to their three meals a day would probably work in the direction of losing weight. Even while sleeping, energy is used more towards digestion and absorption, which may result in decreased cellular regeneration and the synthesis of protein and lipids.