What Happens In Your Body When You Fast For Days

Are you looking for a way to jumpstart your weight loss program?  Fasting for several days will put you on the track to success. However, fasting does so much more than that. Just to be clear, fasting entails only drinking water or, in some cases, vegetable or fruit juices for a chosen period of time. For the purpose of this article, fasting is referred to as drinking water only, and not eating any food. Have you ever wondered what happens to your body when you stop eating?  This article examines the many physical changes that happen when you fast for days.

During The First 24 Hours

intermittent fasting

In the first day of your fast, your body will begin to use its stored nutrients. After your blood glucose and insulin levels decrease, your stored glycogen will start to be released into your body by your liver. When they begin to run out, your body will begin to switch from glucose to ketones. Within twelve to 24 hours, your blood glucose levels will decrease by about 20%.

Days One To Three

Next, your body switches into fat-burning mode. Your fat cells are breaking down through a process called lipolysis. Ketones are still what are keeping your body going. However, since your brain needs a little glucose to function, your body produces glucose through a process called gluconeogenesis. Your hunger hormone, called ghrelin, begins to decline at this point.

Insulin Resistance Reduces

One particularly helpful benefit of fasting is that it’s been proven to decrease blood sugar levels, thereby reducing insulin resistance. This is important because when insulin resistance declines, your body’s receptivity to it increases. As a result, glucose is transported within your bloodstream to your cells in a more efficient manner.

Brain Function Increases

Research led by Mark Mattso, a neuroscientist at the National Institute on Aging, was conducted on mice to determine what effects intermittent fasting has on the brain. Intermittent fasting involves periods of fasting and eating. The mice who were tested showed an increase in alertness and brain activity in areas involved in memory and learning. Their brains also showed a 50% increase in a brain chemical called BDNF. Low levels of this natural brain chemical are common in those who have Alzheimer’s disease.

Increasing levels of BDNF in the brain promotes the production of new neurons and a better connection within them. The bottom line is that fasting offers improved cognitive benefits.

Inflammation Levels Decrease

Inflammation in the body is responsible for the development of certain chronic conditions, such as type 2 diabetes, atherosclerosis, and Alzheimer’s disease, to name a few. Researchers at Yale School of Medicine have discovered that when you fast, your body produces a compound that actually blocks part of the immune system that’s responsible for this inflammatory response.

Heart Health Improves

According to Mayo Clinic, fasting regularly for a 24-hour period one to two days a week has the ability to better your risk factors regarding your heart health. Improved heart health is directly connected to the manner by which your body metabolizes cholesterol and sugar. Fasting on a regular basis has the ability to lower the ‘bad’ cholesterol in your blood. Regular fasting lessens your risk of gaining weight and developing diabetes, both of which are factors that contribute to overall heart health.

Metabolism Increases

One of the best aspects about fasting for several days is that it has the ability to boost your metabolism. In fact, one study conducted on 11 men in good health proved that a three-day fast increased their metabolism by 14%. However, fasting long-term has shown to have the opposite effect on metabolism.

HGH Levels Increase

Also known as human growth hormone, HGH is naturally made by the pituitary gland. HGH is responsible for promoting muscle growth and healthy metabolism, as well as giving you strength. If you don’t have enough HGH in your body, you may gain fat and be more at risk for certain diseases.

Fasting has the ability to significantly increase HGH levels in the body. One study on fasting was conducted over several days to monitor changes in HGH levels. After three days of fasting, HGH levels increased by 300%. After one week of fasting, they increased to a whopping 1,250%.


The positive benefits of fasting are crystal clear. From promoting a healthier heart to boosting your metabolism, fasting is a well-researched practice. Provided that you only fast for a few days or practice intermittent fasting, it’s a safe way to improve your overall health.

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