What if eating at night had more of an impact on weight?

You’ve probably heard the phrase “eating at night makes you fat”. Although this adage is not supported by evidence, new research is looking at the impact of the circadian rhythm on weight gain.


A new area of ​​research called chrononutrition is looking at circadian rhythm and its impact on weight gain. According to researchers in this field, the time we eat the food would have an impact on the way our body reacts to the food consumed.


What is the circadian rhythm?

The Earth revolves around itself in 24 hours. Living organisms that have evolved on Earth have therefore necessarily adapted to this reality in order to be able to use energy sources, in particular light, in an optimal way. For example, due to a cascade of metabolic reactions, plants photosynthesize during the day and shut down at night. The circadian rhythm refers to this 24 hour period.

Mammals, including humans, also have several metabolic reactions that follow a circadian rhythm. The main internal “clock” that initiates these reactions depending on the time of day is located in the brain. Specifically, it is found in a section called the Suprachiasmatic Core (NSC).


The cells of the retina inform the NSC of the time of day according to the brightness they perceive. In this way, the NSC can regulate several reactions since we do not have the same physiological needs during the day or at night. It is believed that almost 10% of genes follow a circadian rhythm and could be turned on or off by the main internal clock.


Food influences our clock


In addition to sunlight, other factors could affect the circadian rhythm of several metabolic reactions. Food would be as effective as light in synchronizing reactions.


Studies in rats and mice (nocturnal animals) show that the latter, when fed only during the day, when they should be sleeping, synchronize with meals rather than the night / day cycle. This means that several metabolic reactions that follow the circadian rhythm, including digestion and absorption of nutrients, can synchronize with meals rather than with sunlight, even if the NSC continues to send information. .


Likewise, fatty tissue secretes several hormones in the body to speak to other organs and inform them of the state of its reserves. It can thus control the mechanisms of storage and use of fat reserves. Between 7% and 21% of the genes in adipose tissue follow a circadian rhythm.


Leptin and ghrelin are two hormones. The first is secreted by adipose tissue and the second by certain organs of the digestive tract. These two hormones follow a circadian rhythm. Leptin is the “appetite suppressant” hormone while ghrelin stimulates the appetite. At night, leptin levels are high in the blood and they drop during the day. This therefore decreases the appetite during the night. The opposite is true for ghrelin. However, the levels of these hormones are also affected by food intake. When we eat at night, ghrelin could increase and leptin decrease, causing several metabolic reactions that usually don’t occur at night (since we are supposed to be sleeping).


In summary, many metabolic reactions are influenced by the time of day through our internal clock, but food intake also influences many of these reactions. So what?


The case of night workers


We speak of “chrono-disturbance” (free translation) when the internal circadian cycles no longer correspond to the circadian cycle of the environment (night / day). This phenomenon is defined by a loss of rhythmicity, a decrease in amplitude in the cycle (between the highest point and the lowest), or by an advanced or delayed rhythm between the organs and the NSC.


This phenomenon is observed in night workers, who no longer follow the sun’s cycle to be active and eat. In this population, overweight, obesity and metabolic syndrome are much more common. Some researchers hypothesize that it is because of this chronic “chrono-disturbance” that night workers suffer more from these problems.


In one study, nine obese men had to eat the same snack, at 9:00 a.m., 5:00 p.m. or 1:00 a.m. When digesting food, our body produces heat. The heat released was measured twice in the participants: one hour and six hours after a meal. Those who ate in the morning gave off more heat than those who ate in the afternoon or at night. This therefore makes it possible to hypothesize that we do not respond in the same way to a meal depending on when it is eaten.


It was observed in rats that the suppression of certain genes directly related to the circadian rhythm of the CNS caused not only a loss of the circadian rhythm, but also metabolic abnormalities similar to the metabolic syndrome. The “chrono-disturbance” of the circadian rhythm could therefore be linked to the high risks of developing the metabolic syndrome in night workers. This of course only remains a hypothesis!


A clinical study in 420 obese people evaluated the effect of feeding timing on weight loss in a 20-week intervention. The patients participated in a program that included group lessons and nutritional support. These were then separated into two categories: those who usually consume their meals early and those who consume them late (after 9:00 a.m. for lunch, after 3:00 p.m. for lunch and after 9:30 p.m. for dinner). Those who ate their meals early lost significantly more weight than those who ate it late. The difference was apparent after 5 th week of the intervention. However, food intake and physical activity were similar between the two groups.


Should I stop eating at night?


These results are certainly interesting. However, the field of chrononutrition is still very little developed. Most of the studies are done in animals and focus on metabolic reactions. The results presented so far allow us to make assumptions, nothing more. There is, however, a definite interest in continuing research in this field, in particular for the health of individuals whose circadian rhythm is disturbed.


It should also be remembered that the total amount of calories ingested in a day has an impact on weight. Thus, if snacks taken after dinner cause more calories to be eaten than those expended, weight gain may occur in the long term.

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