Fasting misconceptions II

Fasting misconceptions II

II)Fasting makes you lose muscle

Since this is one of the most frequent doubts about fasting , and I am sure you came here for this, lets start with the answer:

Fasting doesn’t burn muscle


Why would we believe that fasting burns muscle?

To explain why the spead of this notion we have to start by understanding a pivotal concept, which is “Gluconeogenesis“.  Gluconeogenesis is the process through which with the use of molecules such as fats or aminoacids you obtain glucose. The importance of this process comes from the fact that glucose is one of the main molecules used for energy, specially taking into account the modern high carb diet.

The importance of this concept for us is due to the fact that in the initial stages of fasting, specifically between the 2 and 4 days timeframe since the start of the fast, you see a rise in the use of aminoacids for the obtention of glucose. This is because high carb diets make it so that our body is used to consuming glucose as its main source of energy and this induces the use of other molecules to make up for the lack of glucose resulting from fasting, which is specially accentuated by the deplition of the stores of glycogen, the way in which we store glucose, in our livers and as such a drop in the levels of glucose in blood which is what induces gluconeogenesis.

Answering the question

1)Why burning the furniture is a bad idea?

Now we know where this idea of burning muscle as a fuel comes from, the next step is to understand why it doesn’t make much sense. To begin we have to agree on the fact that muscles are what let you move and go about all the daily activities you have to do, meaning that muscles let you search and obtain the food necessary to keep you alive.

So now that we agree on this fact lets use an example to explain why it would be a pretty bad idea to use muscle as a source of energy. Lets say you are a woodworker and live in a log cabin close to forest and that every week you go to the forest and cut some trees.

Of the trees you cut a part would be used to produce goods you could sell in order to obtain money and live, another part would go to making the furniture for your house and to repair anything borken, and as for the excess you just store to use as firewoood.

Now let’s say one day you are trapped in your house due to a snowstorm and you can’t get out or ask for help and are forced to stay inside. Of course, you already sold all the parts that you could sell for that week and have enough food to keep you going so the only problem is the cold.

Due to the cold, you feel a need to start a fire to warm the house and so you face a choice,

1)You use the furniture you worked on to start the fire or

2) you use the firewood you stored.

So if your answer is to use the firewood, then congratulations, you chose the same as our body does when fasting. In the same way as you wouldn’t use the furniture you dedicated your time and effort to produce, the body wouldn’t rely on the muscle or the so called furniture of the body, but would rather use the fat stored inside since the whole point of storing fat is to use it as a source of energy when there is no food intake and you need energy to keep you going, or in this case to keep the cold at bay.

This simple metaphor can illustrate how using muscle as a source wouldn’t be a good idea, specially since the proteins are not only the furniture but also the house.

Now that we have an answer lets reinforce it with another perspective based on a more biological point of view.


 Ancestor and choices

Photo by Mario Álvarez on Unsplash

To explain the intuitive answer lets use an example, lets say you are one of our ancestors and that you live mostly as a hunter/gatherer. It has been a few days since you last ate and your glycogen stores are running really low and you have to start using a source of energy apart from glucose.

In this situation you have 2 choices, 1) You proceed to use the proteins in your body or 2) You start using the fats you have stored. Of course after having seen the first metaphor you choose the second option, but here lets explain another reason as to why the second option would make sense from a more evolutive standpoint.

Choosing to use proteins as a source of energy is something we actually do all the time as we do use fats all the time and glucose all the time.

That is because the body is always using all three kind of molecules in a sort of equilibrium, being the primary source of energy the glucose if you follow a standard diet and being the fats your principal source if you follow a keto diet or when you fast for long enough.

The only situation in which you would use proteins as your primary source of energy would be in the latter stages of starvation. When you have used all the fat stores and have no other way to provide your body with energy and as such you have to destroy proteins that make you up, remember that proteinsaren’tt only part of muscle but are rather part of all your cells and necessary for the plethora of processes they need to stay alive.

This means that using the proteins in your body would be akin to burnning your house to keep you warm, it could work in the very short term, not really but well, but will cause irreparable damage in the long run. It would certainly debilitate our ancestor and make him unable to search for food and hasten his death.

Data and facts

Many studies have shown that prolonged fasting produces no adverse effects on lean body mass, muscle and bone, and that the only parameter that suffers noticeable changes is the body fat percentage.

Fasting has also been shown to not only not affect the quantity  of protein consumed on a non fasting situation, but to even reduce the protein consumption and to induce a ”conservation” of proteins as we can observe in the graph. This facts back the claim that we don’t burn more proteins during a fasting period.

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Jason Fung, Jimmy Moore ”The  Complete Guide To Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting”.2016. Victory Belt Pub.

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