Sometimes called “fasting,” intermittent fasting is an increasingly popular practice that often involves skipping breakfast or dinner for the purpose of weight loss. What happens in our body during this deprivation? Is this type of fasting recommended? The answers with Professor David Jacobi, teacher, researcher and doctor specializing in nutrition at the Institut du thorax. He is giving this Thursday evening in Nantes a general public conference entitled “Intermittent fasting, when hormones sit down to eat”, on the sidelines of the 38th congress of the French society of endocrinology which is held until Saturday.
What is the link between appetite and hormones?
Let us first remember that a hormone is a product produced by the body that helps it to function and adapt to any situation to which it is subjected. Behind the sensations of being hungry or full hides a whole procession of hormones. In particular, they communicate messages from several organs, such as the digestive tract (stomach, intestine) or fatty tissue, to the brain, which will thus be able to regulate hunger and satiety in an appropriate manner. For example, appetite is stimulated by ghrelin, and inhibited by leptin.
It is the latter that tells us when to stop…
Hormones help us eat the amount we need and ideally no more. But we also eat for pleasure, because it’s good! We can also exercise voluntary control and decide to restrict ourselves, in a weight loss strategy. But this is not always very effective, because it is difficult to go the distance…
Less restrictive, intermittent fasting is an increasingly popular practice, and in which you are interested. Why ?
Intermittent fasting is gaining a certain popularity because we control the moment rather than the quantities, an approach to losing weight while depriving yourself less. It is all the more interesting that scientific knowledge seems to confirm its interest. A 6 a.m. breakfast and 10 p.m. dinner, with a very short nightly fast, is clearly not very good for your weight management and more broadly for your metabolic health (blood pressure, sugar levels , cholesterol, etc.). One way to do intermittent fasting is therefore to reduce the eating window to the best time for the body to absorb, digest and integrate nutrients. Very recent studies have also shown that calorie intake in the morning contributes to better satiation compared to the same calorie intake in the evening. It would therefore be more efficient to keep breakfast rather than dinner, even if it may be easier to do the opposite in relation to one’s personal, social or family organization.
What mechanisms come into play?
What we are trying to do is to have mealtimes in phase with our internal clock (called the circadian clock), which manages all the harmonious functioning of the body over 24 hours. The daily rhythm is divided into two major phases of sleeping and waking, and intermittent fasting is a way to stick to nighttime fasting well. One of the great problems of modern times is that life, social or professional, can disrupt our natural rhythms: we have artificial lighting, refrigerators, food available at all times…
What are the benefits if we get there?
Respecting these rhythms improves your metabolic situation. For example, you will have a better functioning of insulin and will be more sensitive to its action. A good thing because it can reduce the risk of having diabetes. One of the benefits would be a better regulation of your appetite. We also know that the disruption of rhythms will have an impact on mood, fatigue and even depression. Here again, eating well-paced is probably part of good circadian hygiene and can help improve the quality of sleep, managed by two other hormones: melatonin (which promotes falling asleep) which increases in the evening and decreases morning and cortisol (wakefulness), which does the opposite.
So you recommend intermittent fasting to your patients?
We are in a context where metabolic diseases are more and more frequent in the population: obesity, type 2 diabetes… So we have to ask ourselves the question of the new advice that we may be called upon to give. Intermittent fasting, done in a reasonable way (for example by respecting a night fast of at least 12 hours with the most regular schedules possible) with a balanced diet, can make it possible to restructure food intake for a benefit on health. On the other hand, I am much more cautious in recommending more prolonged forms of fasting, the level of scientific evidence being much lower.