Fasting Timeline: Here’s What Happens Inside You During a Day of Fasting
Video | 4-6 Hours | 6-12 Hours | 12-24 Hours
When you fast, your body uses stored energy to run your metabolism, repair tissues, and clean up damaged cells and debris. In this blog post, I walk you through what is happening inside of your body during a day of fasting. You can also download a graphic that summarizes the fasting timeline on one sheet. I think that you’ll find it acts as a great motivator as you progress with your fasting lifestyle.
Fasting Effects Timeline Download
Fasting Effects Timeline
Fasting Timeline: Here’s What Happens Inside You During a Day of Fasting [Video]
In this video, you’ll learn…
- What happens to your body during different stages of fasting.
- Further information on the specific bodily functions that occur during fasting.
- Understanding what our body is designed to withstand!
4-6 Hours of Fasting
Even if you’ve never intentionally fasted before, you have gone through periods of not eating, with the hours that you sleep being the perfect example.
Starting at about 4 to 6 hours, your body begins to react to the lack of food. After these first hours have passed, your stomach has emptied the contents from your last meal, and the hunger hormone called ghrelin is waking up.
Ghrelin is produced by your empty stomach, creating the first subtle wave of hunger. However, ghrelin secretions will ebb and flow, so after that initial wave, ghrelin decreases, and hunger is reduced. Because of this rise and fall pattern, many people find that with a little bit of experience that they can ride out hunger and reach their fasting goal in relative comfort.
6-12 Hours of Fasting
The next phase of events begins to take place 6 to 12 hours after your last meal.
At this time, your digestive system goes into a period of rest. The nutrients from your last meal have been digested and absorbed into your bloodstream where they were met by insulin, which helped to move them to your cells for use or storage. With insulin’s job completed, your pancreas no longer needs to produce as much, leading to low insulin levels.
Your Body Runs on Stored Energy: Glycogen & Fat
Your body can now shift from running on the nutrients from food to running on stored energy, starting with glycogen, which is stored glucose. This first step is orchestrated by your liver to maintain a stable blood sugar level.
However, there is relatively little energy stored in glycogen, so your stockpile of glucose diminishes quickly, and within this first 12-hour window, your body shifts from running on glucose to running on fat.
12-24 Hours of Fasting
This next phase of your fasting experience, which occurs for those who perform 16:8, 20:4, and even one meal a day style fasts is where we see many of the metabolic changes occurring.
Body Fat Burning Creates Free Fatty Acids & Ketones
Within this 12 to 24 hour period, your body is running on stored fat. Some of those released fatty acids can be burned and used directly, while others are converted into ketones by your liver.
Ketones can be used by body tissues, but it is your brain that really thrives on them. This may help explain why some people experience enhanced mental clarity during a fast.
Autophagy Begins & Inflammation Decreases
With the chore of digestion behind us, resources are diverted toward clean-up processes like autophagy, which removes damaged cells and debris.
There is also a reduction in inflammation that occurs throughout the body as well as an increase in the secretion of metabolic hormones, including growth hormone and norepinephrine, which helps to support your metabolism as your day of fasting comes to a close.
The important thing to note is that your body is designed to withstand periods of fasting. In fact, we all fast overnight as we sleep, and our bodies adjust to keep us going until the morning.
By extending that overnight fast, you can encourage your body to run on stored fat, reduce inflammation, and stabilize your blood sugar levels.
Thank you for reading and have a wonderful week!
About the Author
Becky Gillaspy, DC, is the author of The Intermittent Fasting Guide and Cookbook. She graduated Summa Cum Laude with research honors from Palmer College of Chiropractic in 1991.