Intermittent fasting: what is its real effect on the body and how should you do it? The floor to the expert

• Intermittent fasting has become exceptionally popular among celebrities and on social media as a sure-fire way to lose weight.
• You can follow this diet in multiple ways, either choosing to fast through most of the day each day, or choosing to alternate fasting days with regular days, or drastically limiting caloric intake for two days in a row.
• Scientific studies seem to prove the effectiveness of intermittent fasting as a weight loss method over the medium and long term, without changes to one’s own diet.
• Athletic performance does not seem to be hampered by the adoption of this diet and there is some scientific evidence supporting this theory, though academic literature in this field is still really new and uncertain.

Intermittent fasting has become one of the most popular trends in diets and weight loss methods. It promises to make you lose weight and to do it fast. It has also been associated to training workout meant to make your mass leaner and your muscles more defined, without losing their explosive power.

Fitness celebrities around the world, Hugh Jackman, Terry Crews and Beyoncé only to name a few, have all praised its effects and claimed to be staunch users of the diet. Judging by how fit these people are, it might be natural to just believe them and go blindly into a prolonged fast with no rhyme or reason.

What is intermittent fasting?

Intermittent fasting is defined as eating only during certain times of the day or fasting for an entire day. There are numerous kinds of intermittent fasting: the more traditional is the “16/8 intermittent fasting”, or a diet consisting of 16 hours of fasting and 8 hours of eating (Hugh Jackman is a strong advocate of this kind of diet) ad libitum.

It goes without saying that the food you are supposed to eat needs to be healthy: so if your immediate thought was to scavenge for a spoon and the jar of Nutella during your eating time, forget about it. Furthermore, one of the results of fasting may be dehydration, so it is recommended to drink plenty of water (maybe with a bit of lemon juice to add some flavour) and unsweetened hot beverages like coffee or tea during the fasting periods.

Another widely known intermittent fasting diet method is the alternate day fasting. With alternate day fasting, you could eat for 3 days, fast for a whole day, resume eating for two more days and fast for the last day of the week cycle.

Alternate day fasting methods do not necessarily require the complete shutdown of caloric intake: for example, you could drink a lot of juice or rely on low caloric food two consequential days a week. To that extent, Beyoncé’s Master Cleanse and the “5:2 intermittent fasting diet” are the most popular forms of partial alternate day fasting methods.

What are the real effects of intermittent fasting? The floor to the expert

Now that we have clarified what intermittent fasting is in all its forms, it may be interesting to understand the actual effects on the body in terms of weight loss, body mass changes and most importantly on the changes in athletic performance.

To that end, a paper published by Stella Lucia Volpe in ACSM’s Health and Fitness Journal provides an adequate literature review to scientifically prove some of the most direct effects of intermittent fasting on the body.

Intermittent fasting and weight loss

In her paper, Dr Volpe describes the effects of a study conducted by Dr Kelsey Gabel and others, in which he tested the effects of intermittent fasting on 23 obese patients, using the 16/8 method for 3 months. The patients were not following a specific diet and thus the food eaten was they would have eaten on an average day.

The results of his experiment reported that the patients undergoing the intermittent fasting diet witnessed an average net weight loss of 2.6% over the 12 weeks period and a reduction of about 340 kcal per day in their food consumption.

Another study from Dr Volpe’s paper tested the effect of intermittent fasting over a longer period. In this study, conducted by Dr Sundfør and others, 61 people underwent an alternate days fasting diet using the 5:2 method. The result concluded the group reduced their caloric intake by 26% on average and lost 8 kg on average per person.

The results of Volpe’s paper prove that intermittent fasting in all its forms is, keeping the same diet, a sure way to lose weight. However, what is its effect on sport performance?

Intermittent fasting and sport performance

There is a serious concern that athletic performance, both at the gym and outdoor, may be hindered by the use of this kind of diet. This fear is partly due to a partial lack of scientific evidence disproving it, and by the fact that, generally speaking, athletes seem to perform poorly while fasting.

The issue is quite relevant, because some athletes may be choosing to fast, whereas others, due to religious periods such as the month of Ramadan, may be forced to. In a study conducted on a group of Muslim athletes, Zarouk and others gathered biometrics on body composition 1 week before the beginning of Ramadan and during its first and fourth weeks. Furthermore, a series of physical exercises were performed during the study period, to assess changes in athletic performance.

The results of the study showed that, under fasting conditions and keeping the same training routine equal, none of the athletes changed his body mass or diminished his athletic performance, meaning that intermittent fasting does not hinder athletic performance; rather bad timing between fasting periods and training sessions does.