The effects of intermittent fasting on weight loss and body composition

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Obesity is a chronic condition that is known to increase the risk of other metabolic diseases such as diabetes and dyslipidemia. Still, it is one of the main risk factors for cardiovascular diseases. As discussed in some other texts on the portal, its treatment has been evolving significantly with new medications, especially with GLP-1 agonists. However, it is quite evident that the mechanism of action of all anti-obesity drugs is through the inhibition of appetite, in different ways, which means that the purpose of the use of medications in the treatment of obesity is to allow the daily caloric intake to be reduced. within the limits expected to induce weight loss.

Therefore, it is essential in the treatment of obesity to draw up a food plan. Among the proposals, one of them has been gaining prominence both in the lay media and in the scientific environment, intermittent fasting (JJI). And because it is a relatively new topic, but which already has some publications on it, a narrative review was published in the renowned magazine Nature Endocrine Reviews. The study separated the effects of JJI on obesity and body composition and also on cardiometabolic risk factors. For didactic purposes, we have separated the subjects into two topics.

intermittent fasting

Intermittent fasting goals and types

The objective evaluated in this review was the success in weight loss that has clinical significance, that is, a weight loss ≥ 5% of the initial weight (there are other studies and reviews in the literature regarding proposed mechanisms, antioxidant pathways, improvement in overall survival and cancer risk reduction, which were outside the scope of this review) and the impact on associated cardiovascular risk factors.

It is important to note that there are three types of intermittent fasting recommended:

  • Food restriction time (TRA), where the individual fasts for at least 12 h (typically 16 h) per day. The rest of the time, there is no calorie restriction*

*This was the way evaluated in the studies included in the review. It is important to note that in practice there is often a recommendation to restrict not only the time of intake but also the amount of calories consumed during the feeding period.

  • Fasting on alternate daysbeing one day without restrictions and one fasting day (limit of 500 kcal during the “fasting” day, with stimulation of water intake)
  • fast 5:2where within a week, five days are of common food, without restrictions, and two days of fasting (limit 500-1000 kcal).

The last two forms were grouped together because they are part of very similar fasting models and similar results in studies.

The effects on weight

Randomized clinical trials (RCTs) involving models 2 and 3 mostly lasted between 8 and 12 weeks. The result? In general, both produce similar effects on weight loss, leading to a reduction of about 4-8% of the initial body weight. Studies with 24-52 weeks did not observe differences when compared to a shorter follow-up of up to 12 weeks, which may suggest that the maximum weight loss in this strategy occurs around three months of diet.

When compared to diets based on calorie restriction, there was no difference in the percentage of body weight reduction.

On the other hand, studies involving the ART showed a lower success rate, with no RCT showing a loss greater than 5%, reaching an average of 3-4%. It seems disappointing, but it is worth remembering that there was no guidance on caloric restriction during the feeding period in the studies selected for this review.

There is no RCT yet. head-to-head between intermittent fasting modalities.

Body composition

Effects on body composition showed that about 75% of the weight loss induced in the JJI was in fat mass, identical to that induced by calorie restriction.

Another outstanding study highlighted that JJI when associated with resistance physical activity was able to maintain muscle mass (something that cannot be achieved with diet alone) and also significantly reduced subcutaneous fat.

Listen now: Risk of obesity and dysbiosis [podcast]

Is intermittent fasting superior to other forms of diet?

In light of current evidence, there is no such thing as a superior form of diet for weight loss. Even the weight loss in the forms of JJI that achieved significant results in the studies are probably secondary to the induction of a caloric deficit. The best diet is the one that suits the patient and is able to be maintained in the long term, since obesity is a chronic disease (like diabetes, hypertension, COPD, etc.) life.


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# Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol. 2022 May;18(5):309-321. doi: 10.1038/s41574-022-00638-x. Epub 2022 Feb 22. PMID: 35194176.

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She's our PC girl, so anything is up to her. She is also responsible for the videos of Play Crazy Game, as well as giving a leg in the news.

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