Why "When to Eat" Is Important in Weight Management (The Concept of Chrono-Nutrition)


  1. What is chrono-nutrition?
  2. My opinion toward the overall argument

In this article, I would like to introduce the basic concepts of a "biological clock" and "chrono-nutrition" in Japan and consider the importance of eating breakfast.  I will write about “late dinners” in another blog.

Long story short, I recognize the importance of "when to eat, what to eat, and how to eat," and I have no objection to the statement that eating a balanced breakfast is important not only for your health but also for prevention of weight gain.

However, I am uncomfortable with the use of "metabolism" as a catch-all term to explain whether you gain weight or not. Is “metabolism” such a panacea? I believe it should be better explained using my intestinal starvation theory.

1. What is "chrono-nutrition?"

First of all, I would like to introduce the concept of chrono-nutrition from the book, “Clock Gene Diet" by Professor Yasuo Kagawa. Please note that this is only the content from the book and may differ from my own ideas.


(I) The current state of obesity in Japan 

"As of 2012, the number of diabetic patients in Japan is about eight-point-nine million (or twenty-two-point-one million including prediabetics). Diabetes started increasing in the 1970’s.

Then, you might think, “it is because Japan became rich and Japanese people started eating delicious food,” but the average daily energy intake dropped from twenty-two-hundred kcal (in 1970) to eighteen-hundred and fifty kcal (in 2010). 

Nevertheless, the number of diabetics has increased nine fold. Similarly, obesity has increased by forty percent among middle-aged and older adults between 1975 and 2010, even though the energy intake of Japanese people decreased by sixteen percent.

Today, people gain weight not because they eat much. Rather, they gain weight although they eat less."[1]

(2) Discovery of a "clock gene"

"Recent research has unraveled this mysterious phenomenon. It was a discovery of a clock gene of humans in 1997. Not only humans, but also all animals and plants have a “circadian rhythm” in which one day is twenty-five hours.

When we wake up in the morning and the sunlight (blue wavelength) is transmitted to the “central clock gene” in our brain, the twenty-five-hour circadian rhythm is reset to twenty-four hours and the day starts.

However, our internal organs do not receive the sunlight.
By eating breakfast, nutrients spread to every corner of the body, and they inform the “peripheral nerve gene” in each cell of the arrival of the morning, and that resets the twenty-five-hour circadian rhythm to twenty-four hours."

(3) The effect of nutrients differs depending on when they are taken

"In Japan, the term “chrono-nutrition” was used for the first time in 2008 by the Japan Society of Nutrition and Food Science. The more people try to lose weight, the harder they try to decrease the amount they eat from morning until night, but the effect and influence differ significantly depending on the time of day when food is consumed.

From early morning until about four p.m., the body is less likely to store body fat, and after nine p.m., calories are more likely to be stored as body fat.

It is said that the following three are important: ①When to eat (the timing of the meal), ②What to eat (dietary balance), and ③How to eat (the order of eating, the number of meals, etc.)."[3]

(4) Skipping breakfast makes it easier to gain weight

"Breakfast signals the "peripheral nerve genes" in each cell that the morning has come, resetting the biological clock. As a result, body temperature and metabolism rise, and the extra calories taken at breakfast are burned off, so that even if you eat a lot, you are less likely to gain weight.
Moreover, the calories taken in at lunch are also used metabolically, and do not turn into body fat easily, even if you eat a hearty meal.

On the other hand, if breakfast is skipped, the metabolic rate remains slow and the body is prone to weight gain. A calorie-dense meal comes in all at once at noon, and it cannot be converted into energy rapidly, making it easier to accumulate body fat."[4]

(5) What and how to eat

"Eating vegetables first, followed by main dishes such as meat/fish, and then carbohydrates last, prevents a rapid rise in blood glucose levels, making the same menu less fattening.

Eating two meals a day, for example, is prone to storing fat in the body over time. It is better to divide it into multiple portions and eat one small portion at a time, even though it is the same total amount of food.

If you have to eat dinner late at night (e.g. at nine p.m.), it is better to divide your meal and eat carbohydrates by six p.m. and the other side dishes at nine p.m."[5]

2. My opinion toward the overall argument

While the total daily caloric intake remains important, I think it is great progress that people came to understand that even with the same caloric intake, " when you eat, what you eat, and how you eat it" can affect obesity prevention and dieting. And I understand that the time of day we eat can make a difference in the production of hormones.

slim and fat

However, I feel uncomfortable with the use of "metabolism" as a catch-all term to explain the difference between lean people eating breakfast vs those who don’t and being overweight.

Of course, it cannot be completely ruled out, but isn't this simply based on an observational study that examined the degree of overweight between groups of "people who usually eat breakfast" and "those who don't" and just linked that to "metabolic" figures in a correlation?

If eating breakfast boosts the metabolism and consumes all the calories taken in that morning and at noon, then overweight people should be able to lose weight if they eat breakfast. 

According to an intervention study conducted in the U.S. in 2014, overweight or obese subjects were randomly divided into "eat breakfast" and "skip breakfast" groups to see if there was an effect on weight loss, but it seemed that no visible impact was found.[6]

As I mentioned at the beginning, my intestinal starvation theory should be more fitting to explain the benefit of eating breakfast. In the following article, I will explain, “why eating a balanced breakfast leads to the prevention of weight gain” based on my theory.

[Related article]  The Reason Why a Well-Balanced Breakfast Helps Prevent Weight Gain


[1] Prof. Yasuo Kagawa(香川靖雄) , Clock Gene Diet (時計遺伝子ダイエット), 2012, Pages 15-6.
[2]Pages 17-24.  [3]Pages 28-30.
[4]Pages 64-67.  [5]Pages 54-57.
[6] The effectiveness of breakfast recommendations on weight loss: a randomized controlled trial,2014