Intermittent Fasting: What Is It, How Does It Work & Its Benefits

How Does Intermittent Fasting Work?

With its endless list of health benefits, intermittent fasting sounds like a miracle. Is it just a new health myth or does it really work?

A lot of research has been conducted to reveal the actual mechanism behind intermittent fasting, and scientists have discovered that the human body goes through a variety of stages during fasting, activating different mechanisms that lead to a number of perks.

Here are the stages that your body goes through while fasting:

1) Anabolic stage (0-4 hours of fasting)

The anabolic stage (also called the feeding state) involves the first few hours after having your last meal. In this stage of fasting, your body is busy with digestion and absorption of the nutrients that provide energy in your food.

2) Catabolic stage (4-12 hours of fasting)

During the catabolic stage, the digestive process finishes and your body starts looking for alternative energy sources. Glycogen, the stored form of glucose found in the liver and muscles, is your body’s first choice.

Your insulin level falls, which is beneficial for breaking down insulin resistance.

3) Fat burning (12-18 hours)

This is the favorite stage of those targeting weight loss. Your body slowly runs out of the glycogen stores in your liver, so you burn stored body fat.

Plus, as your insulin level has already started decreasing, the growth hormone starts to get released in your blood. This is a powerful fat-burning hormone that preserves your muscle mass and helps burn actual fat.

The most common fasting methods like the 14/10 and 16/8 help you enter the fat-burning stage.

4) Ketosis (18-72 hours)

During the ketosis stage, your body starts breaking down stored fat into molecules called fatty acids and glycerol. Fatty acids can be used for energy. Your liver converts some of the fatty acids into molecules known as ketones, or ketone bodies. Ketones can be used by your brain and other tissues as an alternative source of energy.

When the level of ketones in your blood reaches a certain threshold, your body enters a state called ketosis. In ketosis, your cells rely on ketones for energy, and this is a key characteristic of fasting or a very low-carbohydrate diet.

Ketosis can also lead to reduced appetite, which can make it easier for some people to continue fasting or maintain a calorie deficit. Because your body is primarily burning fat for fuel in ketosis, this state can lead to significant fat loss over time.

If you combine fasting with the ketogenic diet, your body will enter the ketosis stage faster. This leads to increased fat burn and gives you a positive mood and mental clarity.

5) Deep Ketosis (72+ hours)

Although not an easy state to reach, during the deep ketosis phase, many of your body’s tissues and organs, including the brain, adapt to using ketones as their primary source of energy. This means that your reliance on glucose from carbohydrates is greatly diminished.

The suppression in your appetite becomes more pronounced and deep ketosis can lead to ongoing fat loss.

Some people use deep ketosis for therapeutic purposes, such as managing certain medical conditions like epilepsy, type 2 diabetes, and neurodegenerative diseases. The high levels of ketones in deep ketosis are believed to have neuroprotective and anti-inflammatory effects. But bear in mind that reaching this stage is not suitable for everyone and you need to have a period of fasting experience and a  doctor’s approval to abstain from food for over 3 days.

• Autophagy (24-48 hours)

Another important phase your body goes through while fasting is autophagy. This is a cellular rejuvenation process. Think of it as a vacuum cleaner, a mechanism that clears old and dead cells to replace them with new and healthy cells. In other words, your body decides what is necessary and what is going to be rebuilt. See the details of autophagy.

Why Is Intermittent Fasting Popular?

Typical diet plans are hard to follow and they can complicate your everyday life, with lots of snacks to eat between main meals. By switching to the intermittent fasting nutrition system, you:

• save time,
• gain a simplified nutrition regime,
• avoid food restrictions,
• become able to follow your fasting plan wherever you are in the world, as it does not require any specific diet list to follow, and
• there are various methods of intermittent fasting to suit every individual’s needs and lifestyle.

Types of Intermittent Fasting

There are several ways of doing intermittent fasting, based on the patterns of when you eat and when you fast:

The most popular one is 16:8 Intermittent Fasting, which is also called the 16:8 diet or 16:8 plan, where you fast for 16 hours and eat whatever you want during the 8-hour eating window.

Other popular fasting plans include:

• The circadian rhythm diet (12/12 diet)
• 14/10 diet,
• The warrior diet (20/4 diet),
• Alternate-day fasting
• 5:2 diet
• Eat-stop-eat approach

Every individual’s physiology and needs are unique. You can see the fasting types in detail below, so you can choose the one that best suits your needs.

12-Hour Fasting

12-hour fasting is also known as circadian rhythm fasting or the circadian rhythm diet. It simply encourages you to eat in line with your body’s internal clock.

A typical circadian rhythm diet includes a 12-hour fasting period between dinner in the evening and breakfast the next day. The important point is that you should arrange your meal times during daylight hours. This is an easy-to-follow schedule that still offers the weight loss benefits of intermittent fasting. So this is a perfect method for those who are new to fasting and for early birds who can’t skip breakfast.

14/10 Fasting 

Another convenient version of fasting, the 14/10 fasting schedule includes 14 hours of fasting and 10 hours during which you can eat. But there’s no doubt that it’s effective. Fasting for 14  hours a day improves your cardiovascular health and helps you lose weight.

In particular, experts recommend a 14/10 method for women as a starting point, since a longer fasting period can cause irregular menstrual cycles. Note that fasting according to the menstrual cycle is the best method for women who are of childbearing age.

16/8 Fasting 

The 16/8 fasting plan is the most popular regimen among lovers of fasting, and one where you restrict your eating window to 8 hours. Compared to 14/10, 16/8 is more intense and offers more efficient results for those aiming to lose weight.

Studies show that people who implement a 16/8 fasting schedule obtain weight loss (2) benefits and burn fat (3) while preserving muscle mass.

20/4 Plan (The Warrior Diet)

The warrior diet (also called 20/4 fasting) is a real challenge, with an eating window that’s only 4 hours long. An extended fasting period results in significant fat burn and weight loss. In a study conducted with people consuming one meal a day, participants lost weight (4) and gained muscle at the same time.

In addition, compared to 16/8, 20/4 fasting plans boost greater autophagy – a process providing regeneration of healthier and functional cells. But keep in mind that this is an extreme version of fasting and it may be difficult to stick with if you’re a social butterfly participating in social activities like brunch or lunch.

Alternate-Day Fasting (ADF) 

Alternate day fasting (ADF) is an advanced intermittent fasting approach, based on a simple idea: eating every other day. You fast for 36 hours and eat whatever you want during the following 12 hours.

There is some evidence that it may help weight loss (5), but some studies have not found any difference between ADF and a normal calorie-restricted diet (6, 7).

5/2 Fasting 

5/2 fasting is an easier version of ADF. With this schedule, you eat according to your normal routine for 5 days a week and consume only 500-600 calories on the remaining two days. This schedule has various proven health benefits, ranging from weight loss (8) to breast cancer protection (9), and decreased insulin resistance (10).

Eat-Stop-Eat Approach

Another popular and convenient form of intermittent fasting, the eat-stop-eat diet includes fasting once or twice a week. Although there is no direct evidence that this method is effective for weight loss, prolonged fasting may increase your metabolism (11) and thus contribute to weight loss.

There is not an “ideal” method to get efficient benefits from fasting. You’re a unique individual with a unique body, so find your best fit by switching between different fasting types. You can access even more detailed information about different fasting protocols from our article: Intermittent Fasting Schedules for Weight Loss: Which One to Choose? and see before-after pictures of people who follow different fasting schedules from the article: Intermittent Fasting Results: All Schedules Explained.

Or simply get Fasting Kompanion to get a customized fasting plan through a detailed analysis of your personal goals and physiological needs.

How to Do Intermittent Fasting?

Intermittent fasting has a simple logic. Basically, you fast for a certain period of the day and can eat in the remaining time.

According to Dr. Berg, an expert in intermittent fasting and ketogenic diets, the right way to do intermittent fasting involves gradual progress.

If you’re eating 5 meals a day, a sudden decrease to 2 meals a day won’t lead to sustainable change that will help you lose weight. Instead, Dr. Berg recommends switching to 3 meals a day without setting any time restriction, and once you get used to that, limiting the time during which you eat.

If you want to burn more fat, you can then expand your fasting time, having 2 meals a day.

To start practicing intermittent fasting, you can follow these steps:

1. Choose your fasting plan.
2. Start slowly: If you’re new to intermittent fasting, consider easing into it by gradually increasing the fasting duration over a week or two to allow your body to adjust.
3. Stay hydrated: Drink plenty of water, herbal teas, or black coffee (without added sugar or cream) during fasting periods to stay hydrated and help reduce hunger.
4. Choose nutrient-dense foods: When you break your fast, opt for balanced, whole foods that provide essential nutrients and keep you satisfied.
5. Listen to your body: Pay attention to how you feel during fasting periods. If you experience dizziness, extreme hunger, or discomfort, it’s essential to break your fast and eat.
6. Be consistent: Try to stick to your chosen fasting schedule consistently to see the potential benefits over time. Consistency is key to success with intermittent fasting.
7. Monitor your progress: Keep track of your weight, energy levels, and overall well-being to gauge how intermittent fasting is affecting you. Adjust your approach if needed.
8. Consult a healthcare professional: Before starting any fasting regimen, especially if you have underlying medical conditions or concerns, it’s advisable to consult with a healthcare provider or registered dietitian to ensure it’s safe and appropriate for you.

How Does Intermittent Fasting Work for Weight Loss?

We’re quite convinced that there are many benefits of intermittent fasting. But is intermittent fasting good for weight loss? If yes, how does it boost weight loss?

According to the Harvard School of Public Health’s systematic review of 40 studies, intermittent fasting promotes 7-11 pounds (3-5 kg) of weight loss over 10 weeks. (12)

If you’re wondering if intermittent fasting helps you lose weight, let’s dive deeper into the subject and find out how intermittent fasting is a powerful tool for lasting weight loss:

• You eat fewer calories

First of all, the main reason intermittent fasting works for weight loss is that it helps you eat fewer calories.

A study showed fasting plans restricting calorie intake during the night hours significantly boost metabolism and weight loss. (13) And the best bit is that you mostly preserve muscle mass if you combine IF with light cardio exercises such as brisk walking.

16/8 method, 18:6 plan, warrior diet  (20:4), or any other time-restricted feeding plan… They all have one important thing in common, which is skipping meals during fasting periods. This naturally leads to consuming fewer calories in total, which is an easier way than counting calories in traditional diets.

• Your body uses its fat storage for fuel

During the fasted state your body first uses its glycogen stores (stored carbohydrates) as fuel.

As the glycogen level drops, the excess fat in your body will be the main source of fuel and you start burning fat. For instance, if you’re suffering from belly fat, you’ll get rid of the excess fat in that area as you integrate an intermittent fasting diet into your lifestyle.

• Your hormones inhibit your hunger

As your body gets used to fasting in time, you secrete leptin (the satiety hormone) faster and you feel fuller with smaller portions.

Since fasting reduces ghrelin (the hunger hormone), you feel less hungry than usual during your fasting hours. Late-night cravings diminish and you won’t find yourself looking for something to eat.

Intermittent Fasting for Women

Clearly, there are important differences between male and female bodies.

Just as the caloric needs of men and women are different (even for the same daily activity level), their body’s response to intermittent fasting is different, too.

Women’s physiology is more sensitive to calorie restriction than men’s. However many women have experienced great benefits by integrating suitable intermittent fasting plans into their daily lives.

Lasting weight loss is just one of the benefits of intermittent fasting. Reduction of belly fat, improved cardiovascular heart health (14), improved digestion (15), and brighter and younger-looking skin are just a few of them.

So if you’re interested in a complete detox of the old and damaged components in your body for a slimmer and healthier-looking figure, intermittent fasting may be the key to supporting autophagy – a cellular renewal process in which your body removes the old cells to make room for new ones. (16)

However, you should keep in mind that fasting plans with very narrow eating windows may cause hormonal imbalances in some women.

It’s better for women to follow personalized fasting plans according to their menstrual cycles to get the best results out of intermittent fasting and avoid interfering with their hormones.

Starting with a circadian rhythm diet by fasting for 12 hours and having a 12-hour eating window may be ideal for most women.

​​As the body gets used to this system, the fasting window can be increased to 14 hours. With a 14:10 fasting plan, a woman can experience all the benefits of intermittent fasting for weight loss, including the fat-burning stage. To find out more information on intermittent fasting for women, check out our detailed article.

If fasting every day is straining the body, fasting on non-consecutive days of the week can be another method, which is similar to alternate-day fasting (ADF).

You should avoid following an intermittent fasting plan if you:

• are pregnant
• are breastfeeding
• are underweight
• have experienced/are experiencing body dysmorphia
• have excessive levels of stress in your life

If you don’t fit in any of these categories, give intermittent fasting a try for lasting weight loss and many more benefits.

You can get Fasting Kompanion to follow the best fasting plan that suits you.

Intermittent Fasting Meal Plans

Intermittent fasting puts emphasis on when you eat, but what you eat still matters. So schedule your meals to make sure you take in enough nutrients from leafy greens, whole carbs, healthy fats, and proteins.

1) A perfect beginner-friendly plan (12/12, 14/10)

An eating window between 8 a.m. and 6 p.m. provides a warm welcome when you decide to say hello to fasting land. An example plan can involve 3 main meals:

• Breakfast (8 a.m.)
• Lunch (12 p.m.)
• Snack (3 p.m.) – optional
• Dinner (6 p.m.)

2) Intermediate fasting meal plan (16/8, 18/6)

If you get used to the cold of the fasting sea, you can schedule an eating window including two big meals and a snack, starting at 11 a.m. and ending at 7 p.m. Here is an example meal schedule:

• Breakfast (11 a.m.)
• Snack (3 p.m.)
• Dinner (7 p.m.)

3) Alternate-day fasting

Long name, short plan. You just organize a plan that means you eat every other day. Filling your plate with nutritious foods is the key to doing this fasting type correctly. A sample meal plan includes:

• Monday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Tuesday: Fast.
• Wednesday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Thursday: Fast.
• Friday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Saturday: Fast.
• Sunday: Protein, healthy fats, whole carbs, vegetables and fruit.

4) 5-2 meal plan

In this plan, you can pick 5 days on which you eat whatever you want (we encourage you to choose healthy options) and restrict your calorie intake to less than 500-600 on the other two days. Here’s an example of a 5-2 meal plan:

• Monday: Low-calorie day
• Tuesday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Wednesday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Thursday: Low-calorie day
• Friday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Saturday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Sunday: Protein, healthy fats, whole carbs, vegetables and fruit.

5) Eat-Stop-Eat meal plan

First, you choose 1-2 days of the week to fast. You simply consume zero calories on those days and eat normally on the remaining days. Again, make sure that you are consuming healthy fats, enough protein, fruits and vegetables. A sample meal plan looks like this:

• Monday: Fast
• Tuesday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Wednesday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Thursday: Fast
• Friday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Saturday: Protein, healthy fats, whole carbs, vegetables and fruit.
• Sunday: Protein, healthy fats, whole carbs, vegetables and fruit.

Of course, intermittent fasting is a flexible plan so you can arrange your meal times in line with your daily routines. We just want to provide you with a baseline to make clear how to schedule your meals during intermittent fasting.

Side Effects of Intermittent Fasting

In the first few weeks of switching to intermittent fasting, having some side effects is completely normal. The most common side effects of fasting are:

• Hunger:

Leaving your old habit of having 3 meals a day and multiple snacks in between meals is hard in the beginning. New habits take time to settle.

You will feel less hungry as time goes on. Just be patient and drink herbal teas and plenty of water during your fasting hours to make you feel fuller.

• Headaches:

Being hungry for a long period or not drinking enough water during the fasting state may cause headaches in some people.

If the problem persists for too long, switching to a gentler fasting plan with a longer eating window may eliminate this side effect.

• Constipation:

Constipation may be caused by dehydration. Make sure you don’t skip drinking enough water during your fasting hours.

• Mood changes:

Eating is a coping mechanism for some people in times of difficulty. Your body needs some time to adjust to a lifestyle where snacking is not allowed all the time.

• Low energy:

Feeling tired because of hunger is normal in the first few weeks.

Drinking black coffee/ tea or green tea will help you recharge your batteries as they all contain caffeine.

Remember not to add any sugar, creamer, or other additives to your beverage during your fasting period.

• Bad breath:

Not eating for hours may sometimes cause bad breath. Drinking black or green tea helps with this problem.

• Sleep disturbances:

Having a snack late at night is not permitted when doing intermittent fasting, as one of the main features of fasting is to eat in harmony with daylight.

So if you’re a big fan of sneaking into the kitchen and snacking at a late hour, you may experience sleep disturbances, as you may feel hungry while trying to sleep.

You can help yourself with this by drinking herbal teas that promote better sleep such as chamomile, valerian root, lavender, lemon balm, and passionflower.

These side effects are acceptable in the first few weeks. If they persist, switch to a different intermittent fasting plan after consulting your doctor. If your problem with sleep persists, simple tips to deal with insomnia may help.

Other than these problems, there is a suitable plan for almost everyone, unless you;

• are pregnant or breastfeeding,
• are using insulin medicines,
• have type 1 diabetes,
• have low blood pressure,
• have low blood sugar levels (hypoglycemia),
• have other serious chronic diseases that are under treatment,
• have eating disorders or body dysmorphia.

If you are over 18 and do not fall into any of these categories, you will experience great benefits from intermittent fasting.

If you have any hesitations about switching to this “fast and feast” cycle, consult a medical professional in advance.

Benefits of Tracking Your Fast

When it comes to achieving your goals with long-lasting results, tracking your progress is key.

Reminding you about when you should start and end a fast is just one small part of Fasting Kompanion’s tasks.

Creating graphs and charts to make it easier to track weight changes has a big impact on your commitment to fasting. The higher the commitment to your fasting plan, the higher the motivation to achieve your goals.

All the questions that might spring to mind are also answered by the blog articles that are offered to suit your moods and other personal needs.

Kompanion becomes a personal cheerleader to help you along on your unique journey to a healthier life.

In summary, Fasting Kompanion offers:

• A timer to start/end your fasts
• A water tracker
• Tracking of your fasting progress
• Weight tracker and statistics with graphs
• Tracking of your moods at the end of fasts
• Integration with other health apps like Apple Health and Google Fit
• Notification alerts and no advertisements
• Visualization of what happens in your body during fasting
• Visualization of your fasting history
• The chance to stop, restart, or adjust the fast at any time
• Customized blog articles to keep you informed and motivated