Stages Of Fasting

Fasting can provide several health benefits. But, what exactly happens in the body when you fast? In this article, we’ll go over the stages of fasting for you to understand what happens in your body when you go long hours without food.

Intermittent fasting is when you have an eating window and fast the remaining hours you fast.

When you practice fasting, it can help achieve weight loss, improve blood sugar levels, reduce inflammation, and improve digestion. (Source)

A lot of metabolic changes happen whenever you go hours without eating.

Here, we’ll go more in-depth about the stages of fasting to understand what happens in the body when you go long hours without eating.

Different Ways Of Fasting

Intermittent fasting provides you with eating windows and fasting periods.

One of the most significant advantages of intermittent fasting is that it doesn’t rely upon calorie or macro counting. (Source)

Most people believe that during fasting hours, you can eat whatever you want.

And, while this is true, it is one of the most common fasting mistakes.

Relying on fast food doesn’t feed the body as it should, which can increase the risk of nutrient deficiency or chronic illnesses.

While you might include a couple of processed foods during fasting without affecting your goals too much, remember you are what you eat.

Another benefit of fasting is that it doesn’t have a one-size-fits-all.

There are several ways of fasting—each with different eating windows and special considerations.

This allows you to adapt intermittent fasting to your existing routine instead of the other way around.

Here is a list of the most common types of intermittent fasting.

12-Hour Fast

It means not eating for 12 hours.

It is the best way to start for those new to trying intermittent fasting since it follows your natural pattern.

Stop eating after dinner, go to sleep, and start eating the next morning.

For example, stop eating at 7 pm and start eating again at 7 am the next day.

Crescendo Method

This is doing 12-16 hours fast at least every other day and never doing it on consecutive days.

It can be the next step for prolonging their fasting hours.

Additionally, it can be an excellent way for women to start fasting to check its effect on hormones.

In this case, it means fasting Monday, Wednesday, and Friday (or other days you choose).

16:8 Method

It focuses on having an eating window of 8 hours while you fast for 16 hours.

It is one of the most common methods of fasting.

Some people even do an 18:6 method which means having a fast of 18 hours and an eating window of 6 hours.

One Meal A Day (OMAD)

In this method, you only have one meal a day.

While it might be a good option, for some people, it might be challenging to include all the nutrients the body needs in only one meal.

5:2 Method

Here you have 5 regular days but 2 days of fasting.

Some people might not eat anything during those 2 days, while others have a very low-calorie diet, typically 500 calories per day.

Eat-Stop-Eat

This method relies on fasting for 24 hours once or twice a week.

Keep in mind this is an advanced method of fasting, meaning it is not suitable for beginners.

36-48 Hours Fast

Finally, the last time of fasting is when you have a prolonged fast.

It can last 36, 48, and 72 hours.

Most people are frightened to follow long fasting hours since there are a lot of controversies about whether or not it can slow down the metabolism.

However, it shouldn’t have significant repercussions if you do it correctly.

Health Benefits Of Fasting

There is a lot of evidence stating the benefits of fasting.

Here are some of the health benefits backed up by science regarding intermittent fasting.

• Weight loss: A study showed that following intermittent fasting could promote a 3-8% weight loss. (Source)
• Reduced sugar levels: Another benefit of fasting is improved insulin sensitivity which can help have more stable blood glucose levels.
• Improved heart health: Thanks to its effect on cholesterol levels and blood pressure, intermittent fasting can help reduce the risk of heart disease. (Source)

Other benefits of fasting include reduced inflammation, better cognitive function, and it might prolonged lifespan.

However, most of these benefits are seen in animal studies.

So, more human studies are needed to determine the benefits of intermittent fasting.

The Stages Of Fasting

Much like the stages in weight loss, there are four stages in fasting. (Source)

• The fed state
• Pre-fasting state
• Fasting state
• Long-term fasting state

Each stage has a different effect on the body.

Let’s take a closer look at each stage.

1. The Fed State (0-3 Hours)

The fed state happens right after you stop eating.

Here, the body still has some food in the stomach and the system, so it must fully digest and absorb the foods.

The number of hours it might take depends on the food you are eating.

For example, simple carbs such as fruits, sugars, and processed foods (like white bread) take a shorter time to digest.

Typically it might take 30-60 minutes.

This can cause an insulin spike since the body needs to clear the excess sugar in the bloodstream.

Foods like complex carbs (legumes, whole grains, and starchy vegetables), proteins, and fats take longer to digest, usually 1-3 hours.

Here, the body also regulates your hunger levels by decreasing ghrelin (hunger hormone) and increasing leptin (satiating hormone). (Source)

After 2-3 hours, the insulin levels should have returned to normal, as well as blood glucose levels.

2. Pre-Fasting State (3-18 Hours)

Once the body digests and absorbs the food you eat, around the 3-4 hour mark, you start the pre-fasting state.

This stage can last up to 18 hours.

If you are not used to fasting, you might start noticing symptoms such as your stomach growling, feeling lightheaded, or a bit tired.

Typically, these symptoms reduce once you are used to fasting regularly.

After a couple of hours without eating, the blood sugar levels start to decrease.

The body relies on glycogen, a carb found in muscles as a compensatory mechanism.

Once the muscle glycogen levels empty, the body must find other energy sources.

Here, the body might rely on fat stores to provide energy. (Source)

In some cases, the body might turn towards the muscle to use amino acids to provide energy.

3. Fasting State (18-48 Hours)

When you go 18 hours without eating, you are now in a fasting state.

This stage can last up to 48 hours.

Here, all the muscle glycogen is fully depleted, meaning the body has now turned to fats or proteins as an energy source.

One of the advantages of fasting is that as a compensatory metabolic process, the body makes ketones the new currency of energy in the body (since there is no glucose available).

You might be wondering what happens if you do shorter fasting.

If you do shorter fasting hours, then ketones are not produced since you need more than 18 hours (typically 24 hours) to produce ketones.

But, don’t panic.

You can go into ketosis if you follow a keto diet, which means reducing your carb intake to 5-10%, eating protein in moderation (20-30%), and increasing your fat intake (70-80%).

4. Long-Term Fasting State (2-5 Days)

The metabolic adaptations here are for those who are experienced and follow long fasts, typically more than 2 days.

In some cases, this stage is often referred to as the “starvation state.”

Here, insulin levels keep on dropping while ketones rise each time more and more.

Instead, growth hormone increases thanks to ghrelin (the hunger hormone).

It seems this can help preserve muscle mass by reducing the body’s use of proteins as an energy source. (Source)

When you surpass 5 days, you are now in a steady ketone production.

Now, remember that long fasting hours are meant for those who are experienced in fasting.

Also, consult your doctor if you can practice intermittent fasting and which is the best method for you.

How To Effectively Break A Fast

Now that you understand what happens in the body when you practice intermittent fasting let’s talk about what to break your fast.

Foods That Won’t Break A Fast

Before discussing the best foods to help break a fast, let’s discuss the foods you can have while fasting.

Foods without any calories are allowed to have during your fasting hours.

Water, coffee, tea, bone broth, and diluted apple cider vinegar are all great drinks to have during your fasting hours.

They can help you feel satiated.

Also, there are some supplements you can take while fasting, including creatine, electrolytes, and probiotics.

Make sure when you take a supplement, they don’t contain any calories or carbs.

So, read the nutrition label carefully. Technically, you cannot take a greens powder when fasting but vitamins may be okay.

There are some other options that some people might allow, while others say it is a full no-no.

Lemon water with some salt can be an excellent way to stay hydrated during fasting hours.

However, since lemon does contain some calories, some people say it is not suitable to have it during fasting hours.

How To Break A Fast

Now, let’s talk about how to break the fast.

How you break is crucial, especially if you have long fasts such as a 2 or 3-day fast.

Once you are ready to eat, have a gentle meal choice.

This means switching the burger you were thinking of devouring and opting for a food that is easier to digest, such as a green smoothie, Greek yogurt with oatmeal, or a couple of whole grain toasts with eggs.

Having food high in fat or sugar can increase the risk of digestive symptoms such as bloating, stomach cramps, nausea, or gas.

When you have a meal, the body is more likely to tolerate heavier foods such as burgers or other processed foods.

Ensure you don’t rely on processed foods during the day since you need to provide essential nutrients to the body.

Include lean proteins, healthy fats, whole grains, and non-starchy vegetables to ensure you get the required nutrients.

If you suffer from digestive issues, having a lemon shot with turmeric, ginger, and some honey can prepare the body for the food you will eat.

Tips For Fasting The Right Way

Before we finish this article, I want to give you some practical tips I’ve learned while fasting.

Here is some advice I can offer to make this process easier.

• Start small
  It might be tempting to start fasting 18 hours each day. However, you need to train your body. So, if you are new to fasting, make sure you start with only 12-14 hours a day. Once you are a master, you can increase the hours.
• Get busy
  When you reach 18-20 hours of fasting, you might start experiencing hunger pains. Keep your mind busy to avoid focusing on them. Also, tea or coffee can be great allies.
• Plan ahead
  To ensure you are on the path to success, plan your fasting hours and what you will have once you are done fasting.

Final Thoughts

There are 4 main stages to fasting.

The fed state stage happens within the first 3 hours, the pre-fasting stage happens between 3-18 hours, the fasting stage lasts 18-48 hours, and the long-term fasting stage can last up to 5 days.

Each stage has its characteristics that determine the energy source you are using.

Remember that if you want to increase ketone production, they usually don’t happen unless you go more than 18 hours without eating.

If you want faster results regarding ketone production, a keto diet might be a better approach.

Finally, ensure you have a gentle dish instead of heavier foods whenever breaking a fast. For example, choose a protein smoothie, a green smoothie, or some Greek yogurt with fruit to help break your fast without affecting your digestive system.

Brenda Peralta, RDN, CDE

Brenda Peralta is an experienced Registered Dietitian (RDN) and Certified Diabetes Education (CDE). She is a freelance health and nutrition writer based in San Jose, Costa Rica. She has several certifications in sports nutrition, women’s health hormones, and gut health.