Intermittent fasting: what is this strategy to lose weight and what the science says about it

Intermittent fasting: what is this strategy to lose weight and what the science says about it

According to the latest and most important meta-analyzes, fasting is a very useful tool in nutrition. Under this premise appear dietary strategies such as intermittent fasting . Let’s see what it is and what science says about it.

Fasting has scientific endorsement

The myth that it is healthier to eat five times a day is widespread. This is based on a misconception that not starving is healthier, since it does not force the body to "save reserves". However, nothing supports this concept. Quite the contrary. A recent meta-analysis , which analyzes much of the scientific literature published on the subject to date, indicated that the number of intakes has no benefit.

However, cutting back on meals and allowing several hours between meals (in other words, fasting) does. This review looks at various fasting systems and the evidence that supports them. His conclusions are that temporary caloric restriction helps reduce risk factors for various diseases , including metabolic syndrome, cardiovascular disease, cancer, and even neurodegenerative diseases.

Other studies also suggest that reducing the time of intake, and spacing between meals, helps reduce body fat , increase the amount of lean mass (muscle), reduce metabolic age and even help neuroplasticity . All these results are consistent with the conclusions of the meta-analysis that we mentioned, although this one focuses more on vascular and metabolic diseases in adults. Despite the growing body of information on fasting, almost all studies agree that more information is needed.

Many of the metabolic mechanisms are not yet known, although their relationship has been proven. Although there is increasing clinical information, many studies are still based solely on studies with animal models . All these reasons, although they do not undermine the existing evidence, are an indication that it is necessary to continue to better understand fasting and the reasons for its benefits, at a physiological level.

How does intermittent fasting work?

Based on the evidence on fasting, some experts in nutrition and sports preparation design strategies to take advantage of its benefits. Intermittent fasting, or Intermittent Fasting (IF), consists of alternating periods without eating with periods of ingestion at specific times. The best known are fasting 16/8, 24 and 48, but they are not the only ones.

These figures refer to the time between intakes. Thus, the 16/8 fast consists of fasting periods of 16 hours, followed by periods in which we can eat normally for eight hours. If, for example, we have the first meal at 2:00 p.m., we can eat until 10:00 p.m., for 8 hours. Thereafter, we would fast until 2:00 p.m. the next day, 16 hours later. You can eat normally and as many times as you want during these eight hours of intake, although this increases the risk of eating more calories than we would eat in a single meal.

It is necessary to clarify that the intake period is not synonymous with having carte blanche to eat anything and in any way . If we want to lose weight, we will have to maintain a hypocaloric diet. This must be well structured nutritionally speaking, to avoid malnutrition problems. The ideal is to base our diet on healthy foods and not on ultra-processed products, which contain poor nutritional value.

For daily fasts, the strategy is to eat for 24 hours, fast for another 24 , and so on. In short, according to the results of the meta-analysis we mentioned, the important thing is to consume almost the entire diet in a short period of the day, between 4 and 12 hours. It is not necessary to reduce the amount of calories we eat, although it is essential to eat healthy, of course.

This means fasting for 12 or 20 hours in a row , which is the period analyzed that represents the most benefits, according to studies. For example, we could eat for 12 hours and fast for another 12 by bringing dinner earlier and delaying breakfast. Researchers conclude that stopping eating between these 12 and 20 hours can help improve body weight, fat and muscle composition, as well as reduce several processes associated with the disease.

The importance of the circadian rhythm

When we speak of "intermittent fasting" it seems that we are unintentionally pigeonholing this strategy as just another dietary fad. However, the truth is that there is another useful interpretation of its validity. This is related to our circadian rhythm. The circadian rhythm is that kind of internal clock that controls your biological rhythm.

Circadian rhythms control our metabolism through the secretion of melatonin and a cascade of physiological signals. In turn, these rhythms are controlled by light, mainly, although other factors also influence, such as diet. Evolutionarily speaking, the human being has not had availability to eat at all hours until relatively recently.


Our circadian rhythms, in a way, are conditioned by ancient hunting and gathering patterns (or the other way around, probably). The point is that, today, these rhythms are better adapted to a dietary pattern of intermittent fasting, in which you only eat once or twice a day , with a long period of no intake, of activity, than to be eating all day.

This is one more reason why fasting fits into a healthy lifestyle habit. Does this mean that you have to fast? Of course not. The important thing, as any nutrition expert recommends today, is to maintain a series of healthy habits that consider a healthier diet, physical activity and moderation.

Image | Unsplash