Optimize Your Body and Mind: Unlocking the Stages of Intermittent Fasting

Ready, set, fast

Intermittent fasting is an eating pattern that alternates between periods of fasting (only consuming water, tea, or black coffee) and eating. Since it focuses on when you eat rather than what, it can be a helpful eating method for some people. 

Fasting can be done on a daily or weekly basis with various times, typically ranging from 12-hour fasts to more extreme 48-hour fasts. For example, one of the most common types is 16:8, in which you fast for 16 hours a day (including while you sleep) and eat for the other 8. Learn more about types of fasting: Intermittent Fasting: Is It Right for You?

Challenges of fasting

If you’re new to fasting, you may experience some bothersome symptoms. Hunger is common because your body may be used to getting fuel at certain times. You may also get headaches, fatigue and mood changes. This is in part because when we don’t eat for a period of time, we get low blood sugar (1). 

It can be helpful to start with an easier fast, such as fasting for 12 hours a day, for a couple weeks. Remember to drink lots of water throughout the day, and self care including getting a good night’s rest and incorporating gentle exercise (preferably within your eating window). Keep in mind that if you have a health condition, it's important to check with your healthcare provider before trying any new way of eating, such as intermittent fasting.

Phases of fasting

When we fast, our body goes through different stages, each with its own unique benefits. Remember that your body is unique and these phase times may differ depending on your health, activity, and environment. 

After eating: 0-3 hours

Our body gets to work right after eating a meal to break down the food and get those precious nutrients to where it's needed most. The carbohydrates we eat are getting broken down and released into our bloodstream as glucose, or sugar. As our blood sugar rises, appetite hormones also change in order to let our brain register that we are full. 

The hormone insulin also promotes the absorption of sugar for energy and stores the energy we don’t use, as glycogen. Glycogen is stocked in our liver and muscles for times we need it, like exercising. If those stores are full, the leftovers will be stored as fat. 

Start of fasting: 3-8 hours

About three to four hours after we eat, our body is still working hard to digest, use, and absorb nutrients. During this time the fat storing and blood sugar regulating hormone insulin starts to dip (2). Since glucose has been transported throughout our body and stored by insulin, our blood sugar levels begin to decrease again. Our body switches to using the stored glycogen for energy. 

Fasting state: 9-11 hours

After digestion has finished and our hormones like insulin have settled, we’ll have a short period of rest. Then comes the hormone glucagon. This helps promote the breakdown of that glycogen (the stored glucose or sugar) and turns it back into glucose. This helps maintain the supply of energy for our bodies and brains. 

As this period progresses, this is where the fasting magic happens. When that glycogen is used up, our body switches to burning fat! Our body produces fat burning hormones, breaking down fats into a more simple form so it can be used by our cells to help us function. 

Ketosis: 12-14 hours

It’s keto time! After those fat-metabolizing hormones provided our body with a new type of energy, ketones are being produced. Ketones are formed when fat is broken down. They provide an alternative source of energy to our heart, brain and vital organs. For some people, being in a state of ketosis can help with fat loss, appetite management, and focus (3). 

Autophagy: 16 hours on

This is one of the most well known benefits of fasting, called autophagy. This interesting phase means, “to consume oneself”. It may sound scary but some suggest it might provide health benefits. Old cells get recycled and renewed with this clean up process. It keeps your cells working more efficiently and healthier. Keeping on with this phase can increase the autophagy benefits, but since it's such a long time without food, it’s best to ease into this and consider an ok from a physician. Although more research around this area is needed to see the exact potential benefits and risks. 

Interested in trying a fasting plan and testing the benefits of each stage? Try an intermittent fasting app like Lifesum!

All of the content and media on Lifesum is created and published for information purposes only. It is not intended to be used as a substitute for medical advice or treatment. Users should always consult with a doctor or other health care professional for medical advice.