What are the benefits of intermittent fasting, and when do these benefits kick in? In this article, we will take you through the intermittent fasting timeline, and we will look at how this differs for keto eaters [SPOILER ALERT: The timeline speeds up!]. Read on to find out everything you need to know about the intermittent fasting timeline on keto.
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If you’re reading this about the intermittent fasting timeline, you probably already understand intermittent fasting and the different offshoots from this, such as one meal a day, alternative day fasting, and extended fasting.
If not, check out our beginner’s guide to intermittent fasting on keto, which will take you through all of the information you need.
What Happens To Our Bodies When We Fast?
As we all know, everybody is different. We will all start fasting from a different position, starting weight, BMR, glucose stores, muscle mass etc.
Then there are factors during a fast that may be a factor, such as physical activity, gut biome, metabolic health, if any medications are being taken etc, so the results for every one of us will be different.
The keto intermittent fasting timeline is no different, we will all hit some of these milestones at different times.
Life would be boring if we were all the same!
Firstly, we will go through what happens to the body when fasting, assuming that you are not already eating a keto or low carb diet, then we will go through how these time scales can be accelerated if you are already eating a keto diet, are in ketosis and are fat adapted.
Intermittent Fasting Ketosis Timeline
| Time | Bodies Reaction |
| 4-6 hours | Blood glucose drops |
| 10-12 hours | Liver glycogen used |
| 12-14 hours | Rise in ketones |
| 18-20 hours | Fat oxidation increases |
| 22-24 hours | Liver glycogen depletion |
| 24 hours | Gluconeogenesis progresses |
| 4-36 hours | Growth hormone (HGH) spike |
| 36-48 hours | Autophagy increases |
| 48-72 hours | Ketosis deepens |
| Day 3 | Gluconeogenesis peaks |
| Day 3-5 | Ketones rise |
| Day 3-5 | Blood sugar is at its lowest |
| Day 5+ | Growth hormone flattens |
| Day 7 | Metabolic acidosis |
Let’s break these down to better understand what is happening at each stage.
Stages of Intermittent Fasting
4-6 Hours – Blood Glucose Drops
This is all part of the process of getting into ketosis. The body will burn through any glycogen stores in the body.
10-12 Hours – Liver Glycogen Used
Glycogen is mainly stored in the liver and the muscles. It provides the body with a source of energy when blood glucose levels decrease.
12-14 Hours – Rise In Ketones
Insulin helps fuel the body’s cells by converting sugar into energy. When there isn’t enough insulin, ketones build up.
18-20 Hours – Fat Oxidation Increases
Fat oxidation refers to breaking down fats into energy.
22-24 Hours – Liver Glycogen Depletion
Glycogen depletion happens when the body runs out of glycogen stores because of lack of food (due to fasting OR eating reduced carbs), or due to intense exercise which has used up the body’s glycogen supplies.
24 Hours – Gluconeogenesis Progresses
Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate metabolites. In simple terms, this is the process by which the body creates carbohydrates (glucose) from fat and protein.
24-36 Hours – Growth Hormone (HGH) Spike
Several studies have shown that fasting leads to a major increase in HGH (human growth hormone) levels.
HGH is responsible for maintaining, building, and repairing healthy tissues in the brain, as it helps regulate body composition, fluid balance, muscle, and bone development.
36-48 Hours – Autophagy Increases
Autophagy is a natural process by which our bodies clean out damaged cells so that new, healthier ones can be regenerated.
48-72 Hours – Ketosis Deepens
When your body doesn’t have any carbohydrates available to use for energy, it goes into a state called ketosis. Instead, it burns fats and produces ketones, which it uses for energy.
This has already started between 12 and 14 hours, and between 48 and 72 hours, this process intensifies with more ketones being produced.
Day 3 – Gluconeogenesis Peaks
This process started around hour 24, but intensifies, and reaches it’s peak at around 72 hours.
Day 3-5 – Ketones Rise Rapidly
Ketones continue to rise.
Day 3-5 – Blood Sugar The Lowest
All blood sugar reserves should have been burned through by this time.
Day 5+ – Growth Hormone Flattens
HGH has reached its peak and now starts to plateau.
Day 7 – Metabolic Acidosis
Fasting-induced hypoglycemia is associated with the search for an alternative energy source in the absence of glucose and glycogen.
Free fatty acids are alternate sources of energy for the body, which leads to the production of ketones. Ketones accumulate and lead to the formation of acidosis.
Check out this guide for more on intermittent fasting terms, keto terms, and keto abbreviations.
Keto Intermittent Fasting Timeline
For anybody who is eating a low carb diet, they will already be limited glucose in the body. Those who have been eating a keto diet for any period of time should already be in a state of ketosis.
This means that the fasting timeline is already accelerated. This means that some of these milestones will happen at an earlier stage.
Unfortunately, there have been no studies to date that have looked at the difference in the fasting timeline for those that already are eating a keto diet.
If a study has been conducted on this, please let me know in the comments below, I would be really interested to read it.
Although, there have been studies that highlight the benefits of combining the keto diet and intermittent fasting.
What Are The Benefits of Fasting?
There are a whole host of benefits of fasting, we have listed some of the main ones below.
Fat Loss
As your body transitions to using fat for fuel (known as becoming fat adapted), your body will be burning through your fat supplies. This reduces the amount of fat in the body and can be measured by tracking your fat percentage.
Muscle Definition
This links in with fat loss above. The more fat you lose from around your muscles, the more you will see the definition of your muscles. This is why extended fasting is often used by bodybuilders, before a competition.
Rebuild Your Immune System
Extended fasting for 72 hours has been shown to have a significant impact on the immune system. It encourages the repair and renewal of cells that support the immune system.
Deeper Ketosis
Ketosis is when your body uses fat for energy instead of glucose. Entering into ketosis is what everybody eating a keto diet is seeking to achieve. Deeper ketosis brings with it its own list of health benefits, allowing the body to repair and regrow.
Increased Autophagy
Autophagy is a process where cells degrade themselves through lysosomes. This process helps the cell recycle damaged proteins and organelles. The process of autophagy is essential for cellular homeostasis and survival.
Reducing Inflammation
Fasting helps reduce inflammation because it causes the body to release hormones such as glucagon, which reduces blood sugar levels. This leads to lower insulin levels, which decreases inflammation.
Resets Gut Microbiome
By fasting for 24 hours, or longer, our bodies begin to detoxify and cleanse themselves from toxins. When our gut microbiome is in balance, our guts will help us digest food easier, leading to less bloating and discomfort.
Mental Clarity
After your body cleanses itself of toxins, your mind has access to a cleaner bloodstream, which results in clearer thoughts, faster processing, better memory, and sharper senses as a whole.
Hormonal Balance
Extended fasting gives the body the time it needs to reset its hormonal balance. This can help with a whole host of issues such as mood, and skin condition.
Insulin and Leptin Rebalance
As with the hormones above, the ‘rest’ that extended fasting gives your body allows your body time to reset its insulin and leptin levels.
Weigh Loss
It is unsurprising that one of the outcomes of extended fasting for a period of time will lead to weight loss.
A study completed in 2019 concluded that people who underwent several periods of fasting over a year period lost significantly more weight than those that did not.
Keto Intermittent Fasting Timeline [Key Takeaways]
As above highlighted, there is no end to the health benefits that can be gained through intermittent fasting. It is probably only time health benefits can be achieved in life, by doing nothing!
It was only when I understood it in these terms that I chose to give it a go.
Intermittent fasting: Health benefits for doing nothing – my kind of self-care!
As you can see from the above, the vast majority of health benefits can be seen between hours 24 to 36. What is more, if you are already living a keto lifestyle, it is likely that you will see some of these health benefits earlier that the timescales quoted if you are eating a high, or even moderate carb diet.
Therefore, it could be argued that if you are already eating a keto diet, doing regular 24-36 hour fasts may be more beneficial for your body, rather than regularly putting it under the stress of longer extended fasts.
Maybe consider doing longer fasts 3-4 times a year, in order to allow time for your immune system to start to repair.
Fasting Warning
If you are considering fasting and you are on any medications or have any health issues, please seek medical advice before undertaking any fast.
If you are planning on fasting for 72 hours or longer, please seek medical advice, as fasts of this duration should only be conducted under the supervision of a health care professional. If in ANY DOUBT, please seek medical advice first.
Fasting Ketosis Timeline
If you are already eating a keto diet and are considering combining keto with intermittent fasting there are undoubtedly some major health benefits that can be experienced. Just ensure that you seek medical advice if you have any concerns about intermittent fasting. Be sure to let us know your thoughts in the comments below.
