Today, intermittent fasting is growing in popularity. The word “fasting” is no longer associated with religion and has taken on a connection with a list of health benefits like improving your mood, increasing your energy, increasing ability to focus, and even clearer skin.

So, it’s not new if you might be curious about trying out fasting as well. Before you start, you need to know what fasting will do to your body and how it’ll make you feel.

Here is a detailed description of what happens when you are “fasting”, including the stages of fasting and what you should expect.


There are a lot of different types of intermittent fasting. Some will start fasting for no more than 12 hours. And on the upper limit of the timespan of fasting recommended for fasters, is the 72-hour fast, which is long enough to be considered an extended fast. As you go deeper into a fast, the effects stack.

So today, we’ll focus on what happens to you after a 72-hour fast.


The human body’s main source of energy is glycogen, which is a stored form of glucose, a type of sugar you get from those carbohydrates you eat. After your food is digested, your body breaks down carbohydrates into glucose, which it stores as glycogen in the muscles and liver. As long as you have glycogen stored up, then you have energy for your body to use.

In the few hours after eating, your insulin levels will rise, telling your body to break down glucose for energy. But after 12 hours of fasting, your insulin will drop. A hormone called leptin, which is responsible for telling you you’re full, will also fall, while ghrelin, the hormone that signals hunger, will rise.


It takes between four and 18 hours of fasting for you to burn through your glycogen stores. If that happens, your body now needs to turn to an alternative source of energy.

About four hours after you’ve stopped eating, your body will use a process called lipolysis for energy. Lipolysis breaks down the triglycerides – a type of lipid – in your fat cells and breaks down your amino acid for energy.

After about 18 hours of fasting, your body will transition into a state called ketosis, which is when it starts relying on fat as its primary form of energy. In this process, your body will release ketones that your liver produces from fatty acids to break down fat for energy.

At this stage, your insulin levels will remain low, but your glucagon – a hormone that controls blood sugar levels – will start to rise in order to prevent your blood glucose levels from dropping too low.


After about 24 hours of fasting, your body starts to do something really interesting called autophagy. This is a process, which is when your cells start to get rid of any components that are old, damaged, or functioning poorly.

Autophagy is very important for your health and has been studied to reduce inflammation, kill cancer cells, and clear out the misfolded proteins that are said to cause Alzheimer’s. As autophagy declines naturally with age, it’s thought that fasting-induced autophagy can be a way to reduce the effects of aging. And, indeed, studies have shown that fasting is connected to living a longer life.


Your insulin levels will be at their lowest point. Your ketone levels will increase further and, to prevent muscle breakdown, your body will break down branched-chain amino acids.

The advantages of having your insulin levels this low. Insulin resistance, something that can happen as a result of having prolonged high levels of insulin, can lead to diabetes. So, when you fast, you have a healthier body fat percentage, reduce inflammation, and activate further autophagy.


Once you are at the final stage of your 72-hour fast, you’ll see one more benefit. Your IGF-1 (insulin-like growth factor), a hormone involved in growth and development, will decrease. This can trigger stem cell production, create new immune cells, and reduce oxidative stress, something that is thought to help with cancer and diseases.

Don’t get too excited about all of the health benefits that you will get from fasting, it is important to know that fasting for more than 24 or 48 hours is a serious task that should be done carefully and ideally under medical supervision.


Fasting intermittently is not only benefitial to your overall health, but is something that should be practiced regularly. The entire process gives your body time to recover after heavy or greasy meals. Imagine how much better your body would perform had your incorported fasting into your routine! Why wait?


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