Intermittent fasting at a glance … what you need to know

The Endocrinologist
3 min readFeb 11, 2021


Recently, everyone is talking about intermittent fasting. Influencers, trainers, nutritionists and doctors. Given there is so much information, what is the idea that you should take home?

This is my summary I wanted to do as an Endocrinologist, if you are interested, continue reading.

What is intermittent fasting?

It is an alternative to the traditional way of dieting, called daily caloric restriction, because this strategy is difficult to maintain for long periods of time. What is called intermittent fasting has been proposed as an emerging alternative and a new method to decrease energy consumption.

Is there only one way to do intermittent fasting?

No, there are several ways to do it, there are the following modalities: alternate day fasting, time-restricted fasting and periodic fasting.

What is the best way to do it?

There is no better way to do it, but we can say that alternate day fasting is the most studied form of intermittent fasting in humans and the modality that has been studied the most.

What are the risks and adverse events that may occur if a person does intermittent fasting?

Current evidence allows us to say that intermittent fasting is safe for up to 12 months, although there are few studies that have studied this aspect. It cannot be said that it is safer than daily calorie restriction.

Adverse effects are hunger, lack of energy, headache, lightheadedness, constipation, strong breath, cold feeling and poor concentration. In the case of poorly controlled diabetic patients, it is recommended to suspend some medications on fasting days.

At what time should fasting begin?

The optimal time to initiate is unknown since there are few studies in this regard that allow us to make a recommendation. Some researchers suggest aligning intermittent fasting with the circadian rhythm, but further study is required to make a recommendation.

How long should it be done and how often?

There are no studies that have compared how many days of fasting per week are necessary to improve health. More frequent fasting would likely result in greater energy deficit and weight loss.

What is the effect of intermittent fasting on weight and what has been shown when it is compared to daily calorie restriction?

Intermittent fasting has been shown to effectively lower body mass index, body weight, fat percentage, and total cholesterol in patients who are overweight within 6 months. It is possible that intermittent fasting produces a greater decrease in abdominal circumference compared to daily caloric restriction in obese patients over 40 years of age. Apparently there is no difference between these two methods with respect to lean muscle mass, which means that in both, there must be a minimum contribution of protein to avoid muscle loss.

How much weight loss can you expect with intermittent fasting?

It depends on each patient, but it is around 2.5–10% at 6 months.

Finally, we could say that according to current studies, there is no robust evidence for intermittent fasting to be a recommendation in standard practice by health professionals.

I. Guzmán MD



The Endocrinologist