Intermittent Fasting

The new magic pill for health and performance?

The 2016 Nobel Prize in Physiology or Medicine was awarded to Yoshinori Ohsumi for his research on autophagy. Since then intermittent fasting has received increased overall attention as it is related to autophagy with potential health benefits. If you have been in the fitness game for quite a long time, this is nothing new. Many people have succesfully lost weight with this strategy, but is intermittent fasting the ultimate panacea for health, fat loss and/or muscle growth?


Intermittent fasting alternates longer periods of fasting with time restricted periods of eating. There are several “protocols” out there which can roughly be divided in three categories:

  1. alternate day fasting: 24h fasting window, 24h eating window
  2. whole day fasting or periodic fasting: more than 24h fasting window, for example fasting 2 days a week (5:2 diet)
  3. time-restricted fasting: eating window restricted to a definite amount of hours, for example fasting for 16 hours and eating in an 8 hours window (16:8 diet)

Fat loss

Currently, some people are claiming that intermittemt fasting is THE magical strategy to effortless fat loss. As always reality is more nuanced. For a bunch of people keeping their meals restricted to a defined time window can help restrict their caloric intake making it easier staying in a caloric deficit. Because at the end of the day what matters for fat loss is still “calories in, calories out”. How you achieve this energy deficit is your choice and the best one is the one which is sustainable for you, especially in the long term.

Personally, fasting is nothing for me: I have an average step count of 13000/day, my workouts are very demanding and I always drive by bicycle to work and back home. I feel better by fueling myself at least three times a day, sometimes even four or five. Nonetheless, there is a good study by my colleagues from Graz where alternate day fasting in an ad libitum setup in non-obese people performed very well for fat loss compared to the control group. The two groups were not equated for calories but it confirms that it may be a very valid strategy for a lot of people to control their energy intake without tracking calories.

muscle growth and performance

Even if some dubious influencers claim that fasting increases muscle mass, there is no reason for the body to build such an energy demanding tissue like muscles in a caloric deficit (even if there are some exceptions to this statement)! The appropriate building blocks (=amino acids) are rather used for preventing more delicate tisssues like brain and other organs to starve. In a fasting state the hormon signaling is also rather catabolic, which means breaking macromolecules in order to produce energy, which is the opposite to anabolic, which stores energy and builds tissues.

Therefore it is quite clear that intermittent fasting is not the way to go if:

  • you are an athlete relying on performance: for best performace, you need to fuel your training sessions. Fasting also may increase the risk of injury as well as the cortisol (=stress hormon) levels, impairing recovery. Our body doesn’t enjoy being deprived of nutrients, no surprise that recovery takes a beating.
  • you want to build muscles: fasting is by its nature not anabolic. By what we currently know through research, muscle protein synthesis (MPS) is maximised by eating 3-4 meals a day with protein spread evenly throughout the day. Fasting reduces the opportunities to stimulate MPS, rendering it inferior to non-fasting.
  • you want to prevent muscle loss as much as possible, for example in a contest preparation/dieting setting or while being sick/injured/otherwise unable to train: see above


For the media the equation is quite simple: autophaghy = health, therefore everyone should implement some kind of fasting. While there is evidence that impaired autophagy is related with some types of neurodegenerative diseases and cancer, it is still not clear if fasting really improves health. A lot of the studies in which the health markers of the participants improved through a fasting protocol where done in overweight people , which is a big confounder. As soon as they start fasting, they reduce their calories and drop body fat. Less body fat is clearly associated with better overall health and less risk of cancer and cardiovascular diseases. As said before, for some people it could definitely be a very valid strategy to lose weight and therefore improve their health. In contrast to fruit flies, where the calories of a 24 hours fast are completely compensated on the day after, this does not seem to happen in most humans.

A down-side of fasting is that you have lesser occasions to implement a healthy meal where you include different micronutrient-dense foods. The vast majority of the population does not even manage to get their recommended five-a-days of veggies and fruits (which is already a low bar). If you have only one or two occasions to get your fruit or veggies in, the chance that you’ll get all your micronutrients in it’s quite low. Veggies and fruits are often rich in fibre and eating 500 grams of it in one meal could be challenging, especially for those prone to gut distress.

Yes, there are some (rare) diseases where intermittent fasting is used to combat symptoms, but as long as you are healthy, there likely is no additional benefit for intermittent fasting other than creating an energy deficit and dropping body fat to normal levels. More is not always more!

Stefan’s Personal View:

I never understood how intermittent fasting should be beneficial for health. As long as we make sure that our body fat levels stay in a healthy range, it just doesn’t make any sense for me how depriving our bodies from nutrients should improve health. Life has evolved through evolution and in the “evolution game”, calories are king. Maximising calorie intake and minimising calorie expenditure is the key for success: it improves the health and survival chances for the individual, which is then able to produce more offsprings, creating a evolutionary advantage. Literally survival of the fittest.

Why should there be any mechanism in our bodies that make us healthier for starving? Starving is not something that our body should reward us in a context of our species survival. Starving means less calories to play the game of evolution. Starving means hunger and hunger is, as probably anybody has experienced, a very powerful tool of our body to keep us looking for something to eat. Eating is calories, eating is life, eating is evolution. Maybe I don’t see the whole picture, but still those thoughts make it difficult for me to see anything “special” in intermittent fasting other than it being a strategy for warding off unhealthy body fat levels (that are only obtainable in our modern environment).

Related to this, Chantal and I don’t see the point of trying to “heal” a lifestyle with lots of processed food, alcohol, smoking and lack of sleep by fasting. Do you really think that fasting makes up for all this crap?


Intermittent fasting is for sure a valid strategy for some people to lose fat and mantain a healthy body composition. To our current knowledge it is not the ultimate panacea for health that some self-proclaimed gurus propagate and for performance-based athletes it seems to have more unwanted side effects than benefits. If it is a sustainable way for you to reach your goals, implement it, but for a lot of us it may be far better to eat more veggies and lean protein as well as building a healthy relationship with food.

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