The Pros and Cons of Fasting

People fast for many different reasons. Sometimes the fasting is a religious thing and often a way to demonstrate your devotion or to make a sacrifice. In other situations it is used as a way to make a peaceful protest or a statement and fasting is often used to fight for certain causes. In the final camp are those who use fasting for what they believe to be the health benefits that it can provide – as a way to burn calories or to detox their system.

However this isn’t a clear cut thing and there is some debate ongoing as to whether fasting can indeed be good for you or whether it can actually have more negative impacts on your health. For those who fast for health reasons it is important to know whether they are in fact benefiting themselves or just doing more harm than good. At the same time though it’s also important to make sure that people who are fasting for their beliefs understand the implications it has for their body and how to best counter any negative consequences it may have.

Here we will look in detail at whether fasting is a positive behavior that can help us to lose weight quickly and detox our body, or whether it actually causes harm and how you should avoid this.

How You Fast-Twitch

Remember that different groups fast differently. It is an integral part of many religions from Christianity to Judaism and Islam. At the same time it is used by many dieters and even bodybuilders are now looking at the benefits of fasting one day every week as a way to improve ‘cuts’. What’s important to note here is that different groups will fast in different ways and that fasting for a day is very different to fasting for two or more which starts to have more serious physiological effects on the body. Christians for instance might eat only after a certain time, or might fast while removing only certain aspects of the diet. Meanwhile more extreme weight loss uses might advocate using laxatives to remove the contents of the body and this of course can be more harmful when compared to more mild strategies. In an ‘absolute fast’ the individual abstains from all liquids including fluids and again this is likely to create much more damage.

The most common form of fasting lasts for 24 hours (it has to last at least 24 hours to be classed technically as fasting) and is called ‘water fasting’ meaning you are still hydrating yourself. Here we will look at the various different types of fasting so remember that the specific fasting methods used can change the impact it has on the body.

What Is the Impact on the Body?

When you fast this means that your body will have no new supplies of carbs, protein and minerals/vitamins (apart from the vitamins you might get from your water). The fasting technically begins chemically when the body has used up all the available energy in the food and begins turning to the carbohydrate stores in the body (the fat stores).

However what it’s important to recognize is that your body will eventually run out of these stores too, and that means it needs to look elsewhere for energy to perform just the most basic tasks like breathing and walking. After the carbohydrate stores have been used up the body will then move onto protein stores – meaning the muscles and eventually organs. At this point the fast has ended and the person is technically starving.

Pros of Fasting

In other words then the body will be burning fat stores when you fast and that is seen as a positive for many people. The first benefit of that is of course that the body is losing fat and that in turn has various health benefits as well as aesthetic advantages resulting in a more slim and athletic physique.

This has another benefit too and that’s that it allows the body to detox itself. This is because the fat stores don’t just contain carbohydrates, but also chemicals absorbed from the environment. This might include things like DDT – a synthetic pesticide that can get its way into the environment. When the fat is burned these chemicals are released and eliminated by the body via the urine.

At the same time it is suggested that this can provide the body with more energy. This is because the body does not have to take care of the digestive system any longer – a system which requires a large amount of energy. That then means that the energy can be better used for other processes in the body, for metabolism and the immune system which can help the body to heal and repair wounds. At the same time the energy is more effectively used in protein synthesis and in the repair of damaged cells as less mistakes occur in the DNA/RNA. Growths and tumors will be strangled through lack of support from the body’s resources increasing the chances of autolysis. The production of growth hormone – a chemical that the body produces in order to trigger the building of tissue and healing of wounds – also increases. In the wild animals will stop eating when wounded or ill and this is suggested as a possible reason. When we use fasting we are consciously directing energy away from the digestion and recruiting it for the immune system while at the same time starving the disease and producing positive hormones. Ever heard of the term ‘starve a fever’?

Another effect is that the BMR will drop. This is the ‘basal metabolic rate’ that the body relies on to perform its basic functions such as breathing, beating the heart etc. When this drops (this normally takes around a day) the core body temperature also drops and the body becomes more efficient in using that energy.

Part of the way this works is through the improved function of the mitochondria. The mitochondria is a thin layer that surrounds the cell and which converts converts ATP (adenosine triphosphate – the energy currency of life) into useable energy. This in turn means that the body can get more energy out of the same amount of ATP and that means that it can more effectively run the body on lower amounts of energy.

At the same time the mitochondria also surround the cells and that means that they can protect them from free radicals – increasing the life span of individual cells and preventing damage from ‘free radicals’ that otherwise contribute to aging and cancer-causing mutations. It is for this reason that studies can cause increased lifespans in animals through fasting and that many people attempt to mimic these effects through ‘calorie’ restriction or by fasting one day of the week.

Cons of Fasting

However despite these potential benefits and the support of many advocates, fasting remains a controversial topic and there are also many ways that it can damage your health. Here we will look at some of the less positive health effects that fasting may have.

First of all, although some claim that your metabolism can improve during a fast, it might well be the other way around. The reason for this is that although the metabolism has more energy diverted away from the digestive system, it is nevertheless also likely to cause the body to try and conserve energy. This is a natural reaction – as soon as the body stops getting its regular intake of carbohydrates in such a sudden manner it will seem to the body as though there has been a drought of some sort and that you are unable to get food. Thus with supplies scarce the body will try harder to store the fat around the body as fat. Your body has become more efficient in its use of energy – due to the increased performance of the mitochondria – and so whatever you eat will result in more ‘left over’ calories to be stored. This will undo any good work that may have come from the fasting and that will in turn mean that you return to your previous weight soon after you stop fasting. This then will also mean that you experience a sudden change in weight and fluctuating your weight rapidly is not healthy for the heart.

At the same time there are other health concerns. For instance the body requires more than just carbs to run efficiently – it needs protein and it needs vitamins and minerals. These aren’t stored in fat so the problem is that if you aren’t getting them in your diet… well then you don’t have access to them.

This isn’t a major problem in the long run but here’s something you might not know about your body – when it comes to make a repair on your body it will look for the amino acids in order to do that. And if your body doesn’t have access to those amino acids – right then – then that job simply won’t be done. With something like working out it is crucial that you have access to the protein at the correct time – during the ‘anabolic window’ following a workout. If you don’t then that job will be done poorly with poor materials or it won’t get done at all and you will lose out on growth. In other words fasting might improve protein synthesis, but it also means that for near a whole day your body won’t have access to the proteins it needs to do jobs around the body and that can result in a range of different problems. Likewise it means that your blood levels of sugar will drop resulting in your feeling lethargic and tired, as well as blood levels of iron which can have the same effect reducing the amount of oxygen in your blood and so the amount of available energy. This will also result in a lower blood pressure which can cause dizziness and other problems such as arrhythmia (it is not recommended for those with heart problems). However for those with high blood pressure a reduction could be seen as a good thing. It also means that the effects of medication in your blood can become greater and it is highly important that you check with your doctor before going on any fast as this can have severe side effects.

For the stomach as well being completely empty can present some problems as it can mean that stomach acids are more likely to burn the lining. As mentioned the kind of fast that you perform can result in more severe side effects. For instance fasting which uses laxatives can result in extreme dehydration and further malnutrition. At the same time absolute fasting will also result in cramps, headaches and a dry throat and mouth due to dehydration and is not recommended. ‘Water fasting’ and ‘juice fasting’ are more recommended, as might be using an isotonic drink to restore blood sugar and salt levels. This is a method used to treat those with severe dangerous cases of diarrhea and could be used to limit the negative impacts of fasting.


In other words then when you fast you force your body to start looking elsewhere for fat and to begin becoming more efficient in its use of the energy you do have present. This can result in some health benefits such as improved mitochondrial function and weight loss. However at the same time it also means that your body will be without many important nutrients for at least a short amount of time and this can cause some damage. The effects on the metabolism are uncertain and it could have either positive or adverse effects on weight loss in the long term.

If you are going to fast then it is advisable to keep it under 48 hours at all times. At the same time you should make sure to use juice fasting, water fasting or an isotonic drink to maintain hydration. Fasting on a weekly basis is not highly recommended and particularly as a bodybuilding practice, though fasting occasionally in a safe manner might help to improve energy efficiency and protein synthesis. If you are on any course of medication, have heart problems, are pregnant or breastfeeding then you should not consider fasting until you are healthy again.


  1. This does not seem well researched. Mitochondria are organelles inside cells, not a layer around them. How they can surround cells to protect from free radicals eludes me.

    Also water does not have vitamins in it. Maybe traces of minerals is what was meant.

  2. Agree with the previous post. Multiple unsubstantiated blanket comments and recommendations with no studies referenced.

  3. Nice article, very balanced!

  4. Good article. Explains essence of issue well.

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