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Fasting Benefits by Hour: Complete Guide

When people consider starting intermittent fasting, one of the first questions they ask themselves, and the internet, is “How long should my fast be?”

Some feel quite intimidated by the fact that they would have to, essentially, starve themselves for various health benefits, such as weight loss, mental clarity, improved mood, increased energy, and an improved immune system. Read this article to get the biggest benefits from fasting.

Having a good understanding of how fasting works and the ways that it brings those benefits makes it easier to commit – and there’s no safer and more efficient way to fast than with a plan that is personally tailored to you, based on your needs and goals. However, people with a history of eating disorders should only proceed with intermittent fasting under the guidance of a medical professional.

In this article, we will be talking about how fasting for specific amounts of time affects your body and aids your weight loss efforts.

4 Hours

After not eating for a few hours, the body starts moving from a fed state into the early fasting state. This state is also called the postabsorptive state.

As the body is moving food through the digestive system, the blood sugars that were released into your bloodstream from the early stages of digestion begin to decline. Insulin levels, which have been increased by the pancreas to transport blood sugars into the cells throughout the body, start declining in the bloodstream.

As the body continues to require energy to function, due to the lack of continuous calorie intake, it turns to the excess carbohydrates stored in the muscles and liver for up to half a day’s worth of fuel. These stores, called glycogen, are converted into glucose, which circulates across the body, giving it energy.

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12 Hours

As the early fasting stage is nearing its end, the body starts running out of glycogen in the muscles and liver to rely on for energy. This is when the metabolic switch happens.

Around the 12–18 hour mark after eating, the body needs a new source of energy to keep going. This source is the fat cells in the body.

The process of fat burning to release energy is called ketosis. By using water, the body breaks down fat into glycerol and fatty acids, the first of which then travels into the liver and is converted into ketones to supply the body with energy. Due to fat loss, the body continues to lose weight. Read this article for more information about 12-hour fasts.

24 Hours

After a 24-hour fast, the body is continuously tapping into its fat stores for an energy supply through the process of ketosis.

Also, slowing the process of digestion allows the body to focus on important repair tasks and reduce oxidative stress. As the body is using ketosis to fuel the fat-to-energy pipeline, another process starts happening – autophagy.

Autophagy is a process where the cells in the body clean themselves out. This means getting rid of parts of the cell that aren’t working properly or are simply waste. It helps cells deal with the lack of nutrients by making them use energy more efficiently.

Autophagy and the removal of damaged cells and waste carry many benefits for the body and can potentially remove cancerous cells, reduce inflammation and improve the function of stem cells.

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48 Hours

At the 48-hour mark of intermittent fasting, ketosis is still taking place, and the body is still running its housekeeping by using autophagy, maintaining energy levels through fat burning, helping the subject lose weight, and can reduce inflammation. Hunger levels plummet, and the body experiences increased energy. Read this to find out more about curbing hunger.

One of the most noticeable effects of fasting for 48 hours is increased human growth hormone. Human growth hormone health benefits include a positive effect on metabolism, regulation of immune function, mental well-being, and the aging process.

Another change at the 48-hour mark is the increase in the brain-derived neurotrophic factor gene activity, research suggests. This gene produces a protein, which helps the synapses in the brain improve connections, boosting learning and memory. BDNF might increase up to 3.5 times in 48 hours.

54 Hours

At the 54-hour mark of the fast, the insulin levels in the body have reached their lowest since the start of the fast. Research suggests this helps the body increase insulin sensitivity. By decreasing insulin resistance, the body uses blood glucose more effectively and reduces blood sugar levels with regular intermittent fasting. Read this article to find out more about lowering blood sugar at home. 

At the same time, the body is still working hard at cleaning itself and using the excess fat stores to fuel itself and continue running. Human growth hormone is also steadily climbing.

72 Hours

At the 72-hour mark, the body is working really hard to rejuvenate itself. By the time 3 days of the fast have passed, the body sees significant health benefits such as decreases in glucose level, body weight, and an increase in ketone bodies.

Human growth hormone gradually climbs as the fast continues, going up to 300% three days into the fast. Due to human growth hormone and autophagy, the body is at its highest capacity for cell regeneration and immune cell rejuvenation.

Improving immune cell count and shifting to a “younger” cell profile, essentially exchanging old cells for new ones. The ability of cells to regenerate after 3 days is so strong that intermittent fasting can be prescribed by a medical professional to combat the damage caused by chemotherapy. Cellular resistance to toxin damage in stem cells is increased.

What Is Prolonged Fasting?

Prolonged fasting is a form of fasting which usually takes at least 24 hours and may last multiple consecutive days.

How to Complete a Prolonged Fast?

To complete an extended fast, you have to prepare in advance. There is no better way to prepare than to have a plan that is personal to you based on your needs and goals. A good way to get all the information and help you need for your fast is using an app – and DoFasting is the one. By figuring out your current condition and goals, the DoFasting app offers a personalized, one-of-a-kind way for you to fast safely and efficiently.

This app will help you in preparation for, during, and after your fast so you can continue doing it sustainably and reap all the benefits.

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Fasting for a prolonged period of time has its health benefits: fat loss, more efficient use of energy in the body, cell regeneration, immune system improvement, and better insulin management.

While the longer you fast, the more intense the benefits become, you can achieve many of the same benefits on overall health at a smaller scale through intermittent fasting regularly. You should not attempt a prolonged fast without medical supervision if you have no experience with it. For fasting safely and effectively, choose the DoFasting app.


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This is an evidence-based article that includes scientific citations. DoFasting’s professional writers and editors prepared the content, which a team of medical experts verified to be accurate.

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