A new dietary trend has been hovering over the heads of consumers for a few years, both to lose weight and to improve health prognosis through various metabolic markers. That trend is intermittent fasting.

Intermittent fasting seems simple in the initial approach but offers an endless number of versions or modalities.

Intermittent fasting may sound like keeping your mouth closed, or at least not opening it as many times as we usually do; one of the most classic resources when trying to lose weight.

The origins

Voluntary fasting has nothing to do with starvation: the latter is the involuntary absence of food not deliberate or controlled, and people subjected to starvation have no idea when they can return to eat.

On the contrary, fasting consists in the voluntary limitation of the act of eating.

The consequences of one and the other have nothing to do either.

This is the mystery involved in the toxicological concept of hormesis.

The search for the advantages of eating little, restricting food or fasting voluntarily are inherent in any culture, and in all of them there are ancestral references to their practice.

However, beyond millenary beliefs and practices, science has tried in recent years to confirm the health benefits of a certain controlled fast and, if necessary, to know the mechanisms through which they occur.

Regarding the origins of intermittent fasting as a therapeutic strategy, attention should be focused on the line of research that links caloric restriction with longevity and health prognosis.

Today there are already many accumulated publications that have proven the omnipresent and prominent role of controlled dietary restriction on aging and its associated diseases in virtually all kinds of organisms, from unicellular to humans, through invertebrates, rodents and monkeys.

After all, and in the most theoretical field of the matter, intermittent fasting would try to emulate the real conditions of our ancestors who, far from it, ate as many as five times a day.

The difficult thing is to define how to do it, effectively, and to end up eating less often than usual, especially when you live under pressure from the advice to eat until you reach 5 or 6 daily intakes.

But the issue of intermittent fasting has more crumb, especially when considering the scientific articles of the last decade that have observed the foreseeable benefits and possible harms of following this practice, especially if the fast is not controlled by professionals.

By intermittent fasting, we understand all those actions directed to stop eating for variable periods of time, but in a controlled manner.

Although there are different versions more or less personalized, these are the three best-known ways to perform an intermittent fast

The daily intermittent fast contemplates two slots every day, one in which nothing is swallowed -except foods that we will see later- and another in which “it is allowed” to eat.

Those who propose this type of routines usually recommend starting with a 12/12 strategy, in which they would fast for 12 hours in a row, usually including nighttime rest hours, and allow themselves to eat in the remaining 12 hours.

From there it is usually proposed to progress towards a 14/10 strategy; 14 hours of fasting and 10 in which you can eat to reach the most usual 16/8 or 18/6 and even a 20/4 strategy.

The weekly fast, in which a full day is fasted out of every seven consists of for example, having breakfast on a Tuesday and not eating anything until breakfast on Wednesday.

Another version of this proposes fasting two days a week separated by two and three days in which food is eaten: for example, fasting on Mondays and Thursdays.

The fast of two or three days in a row every month is more difficult, because of the long period of fasting that it implies.

The fact is that although the benefits of intermittent fasting remain controversial, most authors argue that there are no extra benefits due to fasting more than one day in a row and, yes, the risks are likely to increase if you do it for longer periods of time.

The possible benefits of intermittent fasting

Before proceeding, it is important to bear in mind that the knowledge we have of this subject is, for the moment, limited: many of the studies that we will see have not followed the same fasting pattern among those that have been described and, in addition, a good part of them are observational.

That said, these are -in general terms- the benefits that are transferred to intermittent fasting:

  • It facilitates weight loss while preserving muscle mass.
  • Improves some biochemical parameters related to inflammation.
  • Improves some parameters related to the lipid profile, cardiovascular risk or diabetes.

We already have in the scientific literature two reviews that critically address the issue of intermittent fasting.

The first of them is Health Effects of Intermittent Fasting: hormesis or harm? A Systematic Review.

Among other observations, this work concludes that despite the differences in the designs of the studies, the regimes and the results, there is a convergence in them that points towards certain health benefits when the fast is prudent.

The second, a more recent analysis is Metabolic Effects of Intermittent Fasting. It concludes that “intermittent fasting patterns are a promising approach leading to weight loss and improvement of metabolic health in those who can safely tolerate those periods of fasting without eating or eating very little during certain times of the day, at night or during some days of the week.

If its efficacy is finally consolidated, this type of regimen “could represent a promising, not pharmacological approach for the improvement of public health in various aspects “.

The risks of Intermittent Fasting

Following the immobility of the dietary issue by certain professionals, intermittent fasting is observed with suspicion.

Opposing groups promote that intermittent fasting will lead to muscle loss, slow down the metabolism – something undesirable when it comes to losing weight – and that in the long-term it promotes weight gain, can lower blood sugar to dangerous levels, generate headaches and a state of increased irritation or susceptibility, and so on.

In this sense, it should be stressed -as the above-mentioned reviews show- that it is not the same to follow a programmed and calculated pattern of intermittent fasting in well-informed persons, than to submit to the effects of starvation.

It is also not appropriate for any reader to follow any guidelines of this type unless supervised by a physician.

Intermittent fasting is not a diet that you can use to “take off and put” a few pounds, to follow for a few weeks and then forget about the matter.

If intermittent fasting is valid for someone, it must be monitored by a professional – at least in its initial stages – and should be assumed more as a new lifestyle, as for someone at a given time who decides to be a vegetarian.

What to eat when you eat almost nothing

The classic approach during periods of fasting involves not eating or drinking anything except water, coffee, teas or infusions – sugar-free, of course – that can be taken without restriction.

In other perspectives in which whole days are fasted, it is also allowed to ingest a certain amount of food, without exceeding – more or less –  500 kcal / day. This must be done without losing the north regarding the quality of the diet, what is eaten and what is not.

It is preferable to eat real food five times a day every day of your life.

By way of final reflection, it would be difficult for me to believe that in our society, given our circumstances, the question of intermittent fasting will be a collective solution to the problems arising from obesity and non-transmissible metabolic diseases.

At the same time, in those suitable and consistent candidates, it could be a truly useful tool.

Its practice has obtained promising results in concrete and -we must not forget- controlled groups, but there is still a long way to go, as all the publications on the subject point out.

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