What Happens in Your Body When You Fast – Science-based benefits, risks

There are positives and negatives to fasting, encompassing physical and mental health. This is why we should know everything we need to know, both benefits, risks, and potential consequences when it comes to fasting.

person thinking about fasting which holding dessert
Fasting is not for everyone – source

Here is everything you need to know, from benefits, risks, and more. There are people who should not fast no matter what while others may gain amazing health benefits almost instantly. Health is not a one size fits all model.

What is Fasting

Fasting is the period of time when you do not eat. Technically, from dinner to your next meal the following morning, you are fasting. Just look at the word breakfast (aka breaking a fast).

Popular fasting methods include intermittent fasting, in which you have an eating window and a fasting window, such as 12 pm to 8 pm eating, the rest being a fasting window.

What Happens in Your Body During a Fast 

Without further ado, here is what happens in the body when you fast. This will show the biological processes from 5 hours after your last meal, to up to 48 hrs of not eating. Do not attempt an extended fast without medical advice and supervision, and be sure to read the risks associated with fasting later in the article. Fasting is not for everyone and that’s ok.

6-10 hours in

At this point, the carbohydrates from your last meal should have been used as fuel in the body. Glucagon will be released, signaling to the body to release sugar stored in the liver to continue to fuel the body with glucose. Ghrelin hormone may increase at this time, a chemical that signals hunger.

12-16 hours in

At this time, your pituitary gland, a region of the brain, starts to release growth hormones. This delays muscle loss and is responsible for rebuilding and repairing cells. Your body temperature drops around this time as well, so you may feel cold.

About 14 hours in, your liver should have run out of any glucose stored up, and your body will start to use fat as fuel. At the 16 hour mark, your body is reliant on stored fat to fuel it, and the process of autophagy begins. This is when your body gets rid of and recycles junk in the body, including dysfunctional cells, damaged protein, and bacteria.

24-30 hours in

Your body should completely run out of any glycogen and solely be using fat for fuel. Protein breakdown is reduced to also zero in order for the body to project muscle fibers for as long as possible. A state in which fat is used by the body as fuel is called ketosis.

48 hrs in

At this point, observational studies have found improvements in mood, tranquility, alertness, and energy stability.

Above 49 hrs

Above 2 days, going on to 3 or more days, there may be an issue with nutrient deficiency slowly stars, muscle atrophy may occur, and you will start to lose too much fat to support the body. 

Of course, this depends on how much fat you have stored in the first place. Someone who is underweight should not fast at all while someone with more fat storage may feel fine. Regardless, a long fast should not be done without medical supervision no matter what. 

What are the Benefits of Fasting

David Sinclair, a Professor in the Department of Genetics and co-Director of the Center for Biology of Aging Research at Harvard Medical School, speaks highly of the benefits of fasting, skipping meals, etc. Many studies, done on both animals and humans have found many benefits. Fasting, even intermittent fasting or occasional dietary restriction, improves health and reduces the risk of diabetes and heart disease.

Fasting may even increase something called the BDFN protein in the brain, supporting the evidence that fasting increases concentration, mental clarity, and mood.

Researchers from the University of Alabama looked at the effect of fasting on pre-diabetes risk. One group ate from 8 am to 3 pm, the other ate from 7 am to 7 pm. There were no differences in terms of weight, but the group that ate from 8 am to 3 pm had lower blood pressure, a drop in insulin, and a decrease in appetite.

Another study found that a one-day fast a week did induce weight loss, but people were hungry! This means it might be better to eat one meal a day on a fasting day instead of skipping altogether. 

What are the Risks of Fasting

The risks of fasting vary from person to person. A long fast may lead to muscle loss and nutrient deficiency. Some individuals should not fast at all, for example, someone with an eating disorder or a child. A full list of people who should not fast is right below.

Short-term risks include headaches, bad mood, reduced energy, and insomnia. This does not happen to everyone, so just listen to your body and troubleshoot problems.

Tips to Feel Better During a Fast

POV: you are fasting for 24 hrs because of a trend you saw online but give up halfway through due to feeling bad, nauseous, dizzy, etc. 

This is why you should start with intermittent fastings, such as having an 8-hour eating window and a 16-hour fast first before trying something for longer. Additionally, using these tips can help you avoid some of the symptoms of a longer fast. These tips target the keto flu symptoms, which include headaches, irritability, and decreased energy.

  • Hydrate properly
  • Add electrolytes to drinks
  • Add a pinch of sea salt to drinks
  • Lessen workouts intensity
  • Sleep properly

Regardless, fasting can be tough so headaches and decreased moods may occur. These are valid responses that can be troubleshot but not ignored. If you try the fixes below and still feel off, listen to your body, break the fast, and eat something light and nurishing.

Who Should Not Fast

There are people who should not fast at all. Do not fast if you are:

  • Pregnant 
  • Some who is breastfeeding
  • A child
  • Someone that is malnourished
  • Nutrient deficient
  • Have a history of eating disorders

The Takeaway

Fasting, while beneficial, is not for everyone. Learn exactly what happens in the body during a fast before trying to attempt one. If anything, try intermittent fasting to avoid skipping meals while still gaining health benefits.

Remember that health starts from within. Regardless of whether to choose to fast or not, it is important to fuel the body with nutrient-dense meals so it has the best building blocks to repair and grow. Exercise regularly to improve both physical and mental health, practice self-care, and watch how wellbeing flourishes. Fitness is a journey that is all bout progress.

Take care of gut microbiota health as well! A balanced gut improves digestion, nutrient absorption, mental health, muscle growth, and immune health! It can even boost metabolism and clear the skin. Get all your gut health resources here for free today!

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