Table Of Contents

When Does the Body Start Burning Fat During Fasting?

Intermittent fasting has gotten all the buzz as it has become a prevalent form of weight loss. Intermittent fasting is defined as the process of establishing a time window in which foods are consumed and fasting occurs during time outside of the eating window. 

When we do not eat, the body goes into a fasting state. This is when the body starts burning fat for fuel rather than carbohydrates. The brain and other organs need glucose to function. So, when you are fasting, your body releases ketones to provide energy for these organs.

Once you pass this stage, you start getting benefits from fasting, like increased energy and weight loss. Learn more in this article.

When Does Fasting Start After Eating, According to a Nutritionist?

The process of fasting, which refers to abstaining from food and/or water for a period of time has been shown to present other benefits aside from weight loss such as:

  • Providing a boost in cognitive performance 
  • Reducing the likelihood of disease (commonly those resulting from high cholesterol) 
  • Reducing inflammation and difficulties in metabolism 

Intermittent fasting is a flexible form of fasting that allows the consumption of foods and liquids unlike other methods of fasting that totally abstain from eating. 

It is the act of abstaining from food and drink other for stages of water fast. This could range from 12 hours to multiple days.

People often wonder when fasting starts after eating. There are different opinions on this topic, and it varies depending on who you ask. Some say that fasting begins after the last mouthful of food has been consumed, while others say it starts as soon as you eat again after breaking your fast.

Some nutritionists say that the fast stage starts after two hours of eating, while others say it begins after three hours.

The truth is that there is no exact answer to this question. The short duration depends on how much you eat and what you eat. But as a general rule, fasting should start after three hours of eating if you have eaten a large meal or if you have eaten multiple small meals throughout the day.

Finally, nutritionists recommend that you wait two hours before you start your fast after eating a meal. They don’t recommend staying more than four hours before creating your fast after eating a meal.

Intermittent Fasting Hour by Hour – Best Time Zones to Follow  

The first thing to know is that it’s not just about when you eat but also about when you fast. Fasting includes abstaining from food and caloric beverages for a while. Generally, fasting can be done for any length, from a few hours up to several days or weeks. It may be done out of personal preference or religious observance or imposed by an external schedule like an intermittent fasting protocol.

There are multiple methods and time cycles established for intermittent fasting that are effective.

Time Cycles of Intermittent Fasting 

There are multiple methods and time cycles established for intermittent fasting that have been shown to be effective, such as: 

The 16:8 Method

This method involves a prolonged fasting timeline of 16 hours and restricting the time window of eating to eight hours. For most people, this schedule means not eating anything after dinner and skipping breakfast. (Example: Between 12 pm-8 pm eating time, which can give time to fast during sleeping)

The 14:10 Method of Fasting

Like the 16:8 method, this one also involves time windows but indicates a 14-hour fasting window and eating for 10. This means extra time to eat, yet it is beneficial to be mindful of nutrient intake to maximize weight loss results.

Intermittent Fasting 18 hours Method (6:18)

The intermittent fasting 18 hours method is a diet that involves eating during an 8-hour window every day, which means you can eat your first meal at noon and your last one at 8 p.m., for example—this form of intermittent fasting is not as strict as the traditional 16:8 and 20:4 methods. The benefits of this intermittent fasting are that it can be easier for beginners to follow and does not require counting calories or measuring food intake.

The “Warrior” Method (8:16)

This method is actually an inverse of the 16:8 method above in which more time is spent eating (16 hours) and the last meal, usually, a protein-dense meal is consumed around 4:00 pm (or mid-day) leaving the rest of the time to fast. This method is exclusively focused on the type of foods eaten being that it leans towards smaller portions of fruits and vegetables throughout the day, leading up to a larger and hearty meal to end the day. 

The Hourly Benefits of Intermittent Fasting for the Body 

The body goes through two different phases when fasting – anabolic vs catabolic fasting. The body is in an anabolic state when it is fed and then moves into a catabolic state when it enters the fasting mode.

So, the main question is, what happens to the body when one fast and what does the body go through to gain these benefits and sustain energy? According to experts, the body undergoes 10 stages during Intermittent Fasting. Here they are as follows:

stages of fasting

10 Stages Stages of Fasting Responses

  • Stage 01: 0 to 4 hours after a meal – Blood sugar is higher, and the body is flushed with insulin to help remove the sugar and convert it into glycogen. Because there is a spike in insulin, a sugar crash may occur, resulting in feelings of hunger/emptiness. 
  • Stage 02: 4 to 8 hours after a meal – Blood sugar drops to a point of stabilization. 
  • Stage 03: 8 to 12 hours after a meal – Blood sugar returns to normal levels.
  • Stage 04: 12 to 18 hours after a meal – Partial ketosis: The body begins to enter the fat-burning stage instead of sugars or glycogen.
  • Stage 05: 18 to 28 hours after a meal – Ketosis and full fat-burning stage: Fat is starting to be used for energy, you’re in a catabolic fasting zone, and the body creates ketones in the liver. Cognitive alertness begins as well during this stage.
  • Stage 06: 28 to 48 hours after a meal – Autophagy or self-repair of cells comes about. More damaged cells are utilized for energy.
  • Stage 07: 48 to 60 hours after a meal – Growth hormone rises which can aid in muscle growth/repair. 
  • Stage 08: 60 to 72 hours after a meal – Your insulin levels are now back to normal from the initial spike. 
  • Stage 09: 72 to 144 hours after a meal – Immune cells start regenerating and increase protective cell barriers. 
  • Stage 10: 144 to 288 hours after a meal – Emotional mastery over hunger: Your perspective on eating may change resulting in intuitive nutrition.

Also read: What Is Ketosis and How Does it Work?

The Stages of Autophagy and Fasting for Weight Loss

Autophagy is the process of cellular degradation and recycling that breaks down cellular components and recycles them. It is a way for the body to maintain itself.

Fasting is not eating anything for a given time (usually at least 8 hours) or abstaining from certain types of food. It is a natural way to trigger autophagy. Fasting helps our body clean out old cells and reduces inflammation in the body by lowering insulin levels.

There are three stages of autophagy that can be used for weight loss: 

Stage 1: Acute starvation mode. 

Autophagy starts with an initiation stage where the cell will begin to break down its components to recycle them for energy or use them for other purposes. After that, the body has a short window of time to mobilize its energy stores to avoid cell death.

The body enters a fast stage, which results in a reduction in circulating glucose levels and ketone production. The brain shifts to using ketones as its primary fuel, which can result in mental fogginess. It’s important to note that this diet should be followed for only three days or less because it can lead to muscle breakdown and other serious health consequences.

Stage 2: Deprivation mode. 

The second stage is when portions of the cell’s structure are broken down into smaller molecules, like amino acids. The body enters this stage when it has burned through most of its stored energy and starts burning muscle tissue as fuel. 

This process is essential for weight loss, as it will trigger the breakdown of fat cells and release the fatty acids stored in them into the bloodstream, which can then be used as an energy source by other cells.

Deprivation can be induced by fasting phases or eating a low-calorie diet for an extended period (2 weeks). The hunger hormones ghrelin and leptin are reduced during this process, which leads to weight loss from fat tissue and muscle mass due to decreased metabolic activity.

The body will start using fat as its primary energy source instead of carbohydrates or protein, which means losing weight even if you don’t exercise or eat anything.

Stage 3: Rescue mode.

This stage is activated when an organelle or cell needs to repair. The cells will break down their proteins and use them as building blocks to help restore the damaged organelle or compartment. Finally, rescue mode is activated when there are no other options for survival. 

This stage can be used for weight loss because it provides energy to the body through the breakdown of cellular components. 

The Best Fasting Benefits Timeline That Will Help You Get Started

Fasting is not only about losing weight. It’s about getting your body healthy and functioning at its best. Just imagine, 17 hours fast every day for a month is beneficial for weight loss in obese people!

The benefits of fasting are backed by scientific research. For example, it has been shown that intermittent fasting can help you lose weight and improve your health in many ways.

There are many different fasting benefits that you can experience when you start fasting. The list below will help you understand the benefits of fasting so you can create your new diet plan.

1. Increases Your Lifespan:

Intermittent fasting has been shown to increase the lifespan of laboratory animals by up to 30%. Many studies have also shown that intermittent fasting can help prevent chronic diseases such as diabetes, cancer, heart disease, and Alzheimer’s.

2. Improved physical performance:

Fasting does not only help with cognition but also physical performance. Studies have shown that fasting could increase muscle mass and the number of mitochondria in our cells, which will help with physical performance and improve endurance and stamina.

3. Promotes Weight Loss:

Studies show stages of intermittent fasting promote weight loss by reducing appetite and lowering insulin levels while increasing metabolism. It also helps in building muscle mass while decreasing body fat mass.

4. Improves Brain Health:

Animal studies have shown that intermittent fasting helps improve brain health by increasing blood flow to the brain, which improves cognitive function and memory. In addition, fasting will enhance cognitive function and brain plasticity because it increases BDNF (brain-derived neurotrophic factor). Also, it helps protect the brain from Alzheimer’s and other neurological diseases.

5. Decreased risk of cancer:

Studies have shown that intermittent fasting phases could decrease cancer risk by up to 65%.

6. Decreases risk of cardiovascular disease:

Intermittent fasting has also been shown to decrease the risk of cardiovascular disease by up to 76%.

Additional considerations

During this time, ketosis should be maintained by the consumption of foods low in carbs. Higher carbs can lead to more cravings and can trigger the body out of the ketogenic state. Further, consuming liquids such as water and coffee can help to satiate hunger.


Stages of intermittent fasting pose many researched benefits. It is important to know what happens in the body as well as notable physical and mental changes that occur because of fasting. Before beginning any new diet, it is imperative to consult with a physician to see if intermittent fasting is a safe alternative.



Keonna is experienced in creative writing, academic and professional research, and proofreading. Her work has been published in several academic journals and concerns educational leadership/pedagogy. Keonna's expertise is in the literature concerning lifestyle and personal development. She is flexible and open to exploring a variety of subjects and research topics.

Proofreader and Content Consultant / INHC&CIHC

Kimberly Tytyk is a Certified Integrative Nutrition Health Coach (INHC) and a Certified International Health Coach (CIHC). Following decades of personal experience transforming her personal health and achieving remission of autoimmune thyroiditis and PCOS, Kimberly completed her formal coaching training in 2021 at the Institute of Integrative Nutrition. Her passions include deep nutrition, holistic and balanced living practices, regeneration, community-building, and finding bliss — usually in a cuddle with her husband and dog.

Fasting ketosisIntermittent fasting 101Intermittent fasting transformation