It has long been known that calorie restriction (in fats, sugars and proteins) has the power to increase lifespan in several species. American scientists wanted to know which form of dietary restriction between intermittent fasting and calorie restriction would be the most effective and safest to improve human health and longevity. To do this, they analyzed in detail the influence of these two strategies on lifespan, as well as on different physiological characteristics in mice with various genetic profiles. Their observation: the effects of dietary restriction are more complex than expected.
We separated 960 female mice into five groups. Each of them was subjected to a particular diet from adulthood until their death. A first group could eat as much as they wanted, a second fasted one day per week, a third fasted two consecutive days per week, a fourth received a caloric intake 20% less than the normal diet, and a fifth a caloric intake reduced by 40%.
The researchers periodically measured various physiological parameters, such as body weight, the proportion of adipose and lean tissue, energy metabolism, as well as the profile of immune and blood cells.
From a general point of view, they observed that all the food restriction scenarios studied extended the lives of the mice, but “with responses proportional to the degree of restriction”: the 40% reduction in caloric intake came first. , followed by that of 20%, then by the fast of two days, and then by that of one day.
While it has often been claimed that the beneficial effects of dietary restriction on life expectancy are attributable to reduced obesity, researchers have noticed what appears to be the opposite. Instead, weight loss was associated with a shorter lifespan. Also, in older mice, greater body fat was generally associated with increased life expectancy.
“The mice that were the most resistant to weight loss [à la suite de leur restriction alimentaire] had a longer lifespan. […] Our study shows that […] “maintaining body weight, adipose and lean tissue composition, and key immune cell populations are major biomarkers predicting greater longevity,” the researchers point out in an article published in the journal Nature.
They note that mice subjected to intermittent fasting ate more than usual when they were served their food immediately after their fasting period. This compensatory behavior allowed them on average to regain the weight they had lost while they were fasting. Also, the mice on calorie restriction consumed their food as soon as it was brought to them, which lengthened the periods when they had nothing to eat.
“This phenomenon may have a particular influence on longevity and on responses to dietary restriction,” suggests Nicholas Schork, of the Translational Genomics Research Institute, in Phoenix, in a commentary published in the same issue of Nature. Mr. Schork believes it would be interesting to compare a diet in which all the food the mouse is entitled to is served at one time, to a diet in which it is distributed in small portions over a long period of time.
Divergent effects
Also, the different forms of dietary restriction notably improved fasting blood sugar (sugar levels) and energy expenditure, two metabolic changes which are beneficial for health, but which did not translate into a notable extension of life expectancy. . The researchers point out that the effects of dietary interventions could induce divergent effects on health and longevity. “This is a surprising result compared to current knowledge and for which I have no explanation,” admits professor of the department of medicine at the University of Montreal, Pierrette Gaudreau.
What’s more, the researchers noted that “certain properties of dietary restriction that appear to contribute to lifespan extension may actually be detrimental to other aspects of physiological health.” For example, restricting calorie intake by 40% induced a decrease in the abundance of certain important cells of the immune system, which could make the mice more vulnerable to infections and “therefore compromise their survival”, underlines M . “These effects in mice raise concerns about the potential risks of extreme dietary restrictions to humans,” the study authors say. Mme Gaudreau agrees: “A calorie restriction of 40% is not at all recommended for an elderly population, it could even be dangerous for their health. »
Despite the multiple metabolic, hematological and immune effects caused by dietary restriction, it appeared that the genetic profile of the mouse had a more significant influence on lifespan than dietary interventions. “This observation suggests that the response of humans to dietary restriction would vary from one person to another depending on each person’s genetic profile,” the researchers point out.
“It will also be important to study the influence of dietary restriction on epigenetic regulation, that is to say on the level of expression of different genes, in different tissues,” adds M.me Gaudreau, who notes that the study was only carried out in female mice. “However, we do not know if the female is biologically advantaged during aging compared to the male, [et si oui]through the same biological mechanisms or not. »
This aging specialist at the CHUM Research Center does not recommend food restriction for humans, but rather suggests “moderation and dietary diversity at the level of each meal”. You should not ingest more calories per day than you expend. It may seem easy, but ingesting a surplus of calories coupled with a sedentary lifestyle is a free pass to becoming overweight, possibly obesity, cardiometabolic disease and reduced muscle capacity.”