The Ultimate Intermittent Fasting Guide
What Is It & How Does It Work?

What You Need To Know About Intermittent Fasting
Written by Isaac

Let's be honest. How many people actually want to be on a diet?

Sure, it sounds like a good idea in concept and you know that the benefits for your health make turning those donuts down worth it, but the truth of the matter is that restricting what you can eat everyday is a hard mental change to make.

If you're the kind of dieter that hates calorie counting with a vengeance and spends each night dreaming of an endless buffet filled with all your forbidden favorites, then staying on a restrictive diet for the long term is going to be brutal.

For many people there is. In recent years, Intermittent Fasting (IF) has become a new approach to healthy eating has taken the medical world by the storm.

When you follow the principles of intermittent fasting, you don't restrict what you eat, but rather when. And it promises that with a few simple logistics changes in your meal times, you can start to lose weight.

Does this sound to good to be true?

What Is Intermittent Fasting?

The results of intermittent fasting for weight loss can be astounding.

In truth, the pounds aren't going to melt off without any effort on your part. The key to IF is undergoing long periods of fasting where you are restricted from eating calories. These fasts can last anywhere from 16-36 hours and are usually repeated several times throughout the week.

There is a burgeoning population of regular intermittent fasters that have achieved incredible results through this eating practice.

They claim that following this eating methodology has caused them to become healthier, lighter, less prone to disease, and even more muscular and physically fit.

If you want to learn more about this fascinating eating plan, you're in the right place. We've done our research and found the real facts behind the hype of intermittent fasting. So if you're ready to dig into the truth, then keep on reading.

Plate in a clock shape

Waiting for your next meal during an intermittent fast.

To be accurate, intermittent fasting isn't a diet, it's a pattern of eating; a way to schedule your meals so that your body gets the maximum benefit out of each one.

This plan isn't focused on which foods you eat (or often even how much). Rather, it's when you eat that makes all the difference.

The main idea of IF is that you undergo a series of short term fasts to lower the amount of calories you eat in a day while also revving up your metabolism to its full fat-burning potential.

A food fast can be as simple as eating a big dinner and then not consuming anything but tea or coffee until 1pm the next day. Lunch and dinner are then eaten normally after this fasting phase, and the process can be repeated over again.

IF is a surprisingly effective strategy for losing belly fat because it doesn't require you to transform your entire dietary lifestyle.

It's an easy diet to stick to because you can start it with minimal preparation, but the results are so effective that they will keep you motivated for the long term.

As an added benefit, following an IF meal plan supplemented with exercise can help you build up your endurance and gain lean muscle mass.

The History Of Intermittent Fasting

Intermittent fasting may seem like a new idea, but it's actually the way that humans have evolved to eat. Throughout much of history (especially during the days of the hunter-gatherer) food was a scarce resource that couldn't always be counted on from meal to meal.

Early people groups were accustomed to eating big meals when food was available and going without during other times.

In fact, intentionally abstaining from food eventually took on cultural significance, and many of the world's major religions like Islam, Christianity and Buddhism teach the benefits of temporary fasting.

Scientists began to study the benefits of skipping meals in the 1930s, and their studies found that lab mice lived significantly longer when they were given fewer calories to eat everyday.

Recent science has discovered the same impact on insects and monkeys.

Their evidence has been clear; reducing your calorie consumption by a third can reduce your risk of common diseases and even extend your lifespan by decades.

In many ways, the scientific evidence seems to point at intermittent fasting as a more natural way to eat than our modern method of eating 3-4 meals per day.

How Does Intermittent Fasting Work?

The key to intermittent fasting is that it changes when your body is in a fed state and a fasted state. Your body acts differently depending on which state it is in.

After you eat a big meal, your body is in the fed state for three to five hours while it digests and absorbs all the nutrients it can get from your food. This means it won't be turning to its fat stores for energy, especially if you've eaten lots of carbohydrates and starches that raise your insulin level.

Healthy dish on a plate

Not all carbs are created equal.

After your food is digested, your body goes into a post-absorptive state that lasts between 8 and 12 hours after eating.

This is a fasted state, and when food is absent, the body's levels of blood glucose go down significantly. This lowers the amount of insulin that is available, which causes your body to burn through its fat reserves for fuel instead.

Working out in a fasting state is especially beneficial for your body. When you exercise at a time when your body can't draw from its glucose stores, it is forced to adapt and use the other source of energy that's available - your body fat.

If you read carefully, you noticed that it takes our bodies almost 12 hours to enter the fat-burning fasted state. It's rare for people that eat three meals a day to enter this state, meaning they are limiting their fat burning potential.

This is the main reason why people who start intermittent fasting can lose body weight without making any other lifestyle changes like dieting or exercising. Simply by restricting when they eat, they are priming their bodies to be in an optimal fat-burning state.

Is intermittent fasting as simple as skipping a meal once in a while?

Not quite.

The timing between meals can be crucial, as is the frequency of fasting periods. Not all calories are created equal, so the benefits in this diet don't come simply from eating less, but rather from training your body to burn through body fat as efficiently as possible.

Still confused?

To put it simply, intermittent fasting is a process that teaches your body how to best process its energy reserves. By putting yourself in a situation where your body doesn't have a constant supply of fuel, it learns to draw fuel from your body fat.

5 Reasons to do Intermittent Fasting

Maybe you've been trying to lose weight for months without seeing much result. Perhaps the last few pounds are proving to be the most difficult to dislodge. If this sounds like you, your eating habits could be benefited from trying intermittent fasting.

Below are some of the reasons why intermittent dieting might be the right diet plan for you.

1. It's Not A Diet, It's A Method Of Eating

Woman eating at the dinner

Feeling fungry yet?

Regular diets like Weight Watchers or Atkins can be a pain to live with on a daily basis.

Not only do you have to count calories, you need to avoid certain foods and add up your point levels every day. In contrast, intermittent dieting doesn't require any accounting for what you eat.

Rather, you just change when you eat allowing for more flexibility throughout the day. If you can overcome some temporary deprivation, your sweet tooth will thank you for allowing it to sample favorites like wine, cheese and decadent desserts - all without feeling guilty.

Most diets fail because it is difficult to stick to them in the long term.

Because you are never truly giving up your favorite foods when you IF, it's much easier to stick with it for the long term.

2. Your Workouts Might Become More Effective

It may seem counter-intuitive, but working out on an empty stomach may actually make your workouts more effective.

Exercising on an empty stomach supercharges your bodies fat-burning abilities, allowing you to shed more weight in less time.

3. Your Eating Plans Become Simpler

A sign on a fridge saying: Come back tomorrow

It's been known for decades that restricting calories can help you live longer.

Intermittent fasting allows you to make big changes to your body's fuel efficiency with only minimal changes of behavior.

You will have fewer meals per week to worry about, and you rarely need to calculate what goes into each meal.

By eating fewer meals, you'll be doing less cooking and consequently do less grocery shopping. Saving the time each day that would normally be spent preparing and eating food can add up over time.

4. You Can Stave Off Emotional Eating

If the restrictive nature of most diets causes you to binge on cheat days, IF might be a good diet plan for you.

Studies have shown that when people followed an IF diet combined with exercise, they decreased their levels of emotional eating and were less likely to make harmful food choices.

5. You Just Might Live Longer

It's been known for decades that restricting calories can help you live longer, and IF makes eating less easy and painless.

It activates the same mechanisms for extending your life as restricting your calories, all without the benefit of feeling like you have to deprive yourself.

6 Types of Intermittent Fasting Diet Plan

Starting an intermittent fast is easier than most people think. Simply cut out some of the times that you eat food and experiment until you find what feels right for your body.

Some people do better with a small breakfast at the beginning of the day, while others are able to skip food entirely until the afternoon. The key is to try different methods until you find what your body responds best to.

Though you won't necessarily be counting calories for your meals, it's a good idea to focus on eating high fiber, high protein foods before and after fasting to keep yourself feeling full without needing to eat too many extra calories.

Additionally, soups are a great food for fast days when you eat small meals because they will make you feel fuller than eating the same ingredients in a different form.

Fork and spoon tatoo on arms

Extremes are easy. Strive for balance.

There are several types of intermittent fasts, all that rely on different intervals of time between eating and fasting. Six of the most popular diet plans are explained below.

1. Daily 16/8 IF (Lean Gains)

As one of the most popular fasting methods for beginners, the Lean Gains method was created by Martin Berkhan as a way to make fasting both convenient and habitual.

The premise behind this diet plan is simple; dieters don't eat anything for 16 hours and then eat within an eight hour eating window - sometimes referred to as 16/8 fasting.

Most people eat their last meal of the day around 8pm and then fast through the night and morning until 1pm. For maximum fat-burning benefit, some people choose to workout around 11am or noon.

You can also focus your fast in the afternoon by making your eating period last from 8am to 4pm; the timing is less important than the ratio of eating to fasting.

As the name implies, 16/8 intermittent fasting produces the best results when it is done every day, which makes it easy to set up a routine.

A snapshot of a before and after doing Lean Gains, taken from Youtube.

Before and after Lean Gains.

It's also one of the best fasting plans to integrate into normal life, especially if you skip breakfast. Because lunch and dinners tend to be communal meals, you won't have to worry about your fast affecting social events.

Though intermittent fasting for weight loss works very well, it can put athletes at a disadvantage because skipping a meal everyday makes it difficult for them to eat enough calories to maintain their muscle mass.

To avoid this problem, Berkhan recommends eating higher protein meals on days when you work out and focusing your diet on carbohydrates over fat.

  • Advantages: This diet plan is simple to follow and requires minimal lifestyle changes. It also gives you the flexibility to eat as much as you want during the eating periods.
  • Disadvantages: If you're working out frequently, the dietary requirements are much stricter. Many people also find it difficult to work out at the end of 16 hour fast, which might make it easier for you to skip your workouts.

2. Weekly IF (Eat-Stop-Eat)

An easy way to start venturing into fasting is to try it out once a week or even once a month. The Eat-Stop-Eat fast was created by Brad Pilon and is ideal for healthy eaters looking to get an extra boost out of their diet.

The simple premise is that followers of the plan go on 24 hour fasts for one or fewer days every week.

Some practitioners fast as just a few times a month.

Surprisingly enough, even occasional fasts like this has been shown to lead to the health benefits, so even if you aren't ready to commit to a daily fast you can still make yourself healthier in the long run.

The idea is that by cutting out a day of eating every once in a while, you will be restricting your overall calorie levels, even if your daily eating habits remain unchanged. However, for this diet plan to be effective you need to be getting regular exercise to ensure you aren't adding all your missed calories back to your diet with a big post-fast feast.

Weekly fasts allow you to eat whatever you want every day of the week besides one day when you fast for a full 24 hours.

During this time you are allowed to drink no calorie beverages like coffee and tea, and possibly chicken bouillon if you need to refresh your salt levels.

Eat stop eat logo on a white background

A benefit of 24 fasts is that you don't have to do them on a regular schedule. For example, they can be especially beneficial after a big holiday meal or while traveling.

  • Advantages: The Eat-Stop-Eat plan is flexible and allows you to try out fasting without committing to a daily routine. You can also work your way up to 24 hours over time and start with a time that is more comfortable for your body. No calorie counting or meal-time planning is required.
  • Disadvantages: Some people find it hard to go 24 hours without food, and attempting to fast makes them cranky, anxious, foggy-headed and prone to headaches. (These side effects diminish the more you practice fasting). You need lots of self control to follow through with this diet plan.

3. Alternate Day IF (Up Day, Down Day)

Created by Doctor James Johnson, the Up Day Down Day fasting program is all about weight loss and is structured to cause you to lose as much weight as possible in a healthy way.

The idea is that alternating the amount of calories you eat everyday activates the SIRT1 gene, which some studies show helps prevent your body from putting fat into long term storage, causing you to stop putting on weight.

This meal plan is simple to follow. You alternate each day from eating a normal diet to eating one fifth of the calories you ate the day before. For most men, this means they eat 2,500 and 500 calories every other day, and for women the levels are 2,000 and 400.

Tomato soup on a table

Soups are great food for fast days.

Followers track their calorie counts every day to stay on track, and limit the difficulties of their workouts on fast days.

Dr. Johnson recommends that dieters drink meal replacement shakes on fast days for the first two weeks to get used to the routine before switching over to real food afterward.

This diet plan can be followed indefinitely or until you hit your target weight level. An alternative is to cut out calories entirely on the lower calorie days, but this should only be followed with caution and after you have gotten your body used to the less extreme version first.

  • Advantages: When followed correctly, this meal plan makes it easy to lose weight. The participants in Dr. Johnson's study averaged 2.5 pounds of weight loss every week they followed the fast.
  • Bullet Point Disadvantages: Some people find it troublesome to monitor their calorie counts everyday, and it can be easy to overeat on your regular eating days.

4. The Warrior Diet

As its name implies, the Warrior Diet is for the truly devoted who are as interested in getting muscular as they are in losing weight. Started by Ori Hofmekler, the plan combines a 20 hour fast with a four hour eating window for eating.

The reasoning behind the long fast is to increase the functionality of the sympathetic n system (the part of the body responsible for fight-or-flight tendencies) in order to stimulate lipolysis and increase the metabolic rate of fat burning.

This helps the body to absorb glucose properly and recover more efficiently after a big workout, while also increasing your alertness and boosting your energy levels.

Unlike other fasting plans, the Warrior Diet requires followers to eat their meals at a specific time of day, in this case at night.

Woman holding sward on a white background

Carbohydrates should only be eaten if you are still hungry after your meal.

This is based on the philosophy that the body performs best when it is fed nutrients while in sync with circadian rhythms because of our biologic history as nocturnal eaters (just like most other carnivore mammals.)

The fasting periods for the Warrior Diet are less about not eating and more about under-eating. Raw vegetables and fruits, juice and small amounts of protein are all allowed during the 20 hour periods.

Practitioners then eat monster meals during their four hour eating time and focus on filling themselves with high quality ingredients filled with protein and healthy fats.

Carbohydrates should only be eaten if you are still hungry after your meal.

  • Advantages: The “fasting periods” in the Warrior Diet still allow you to eat food, and when followed properly with strength training exercise, you are likely to bulk up.
  • Disadvantages: Eating one monster meal a day can be hard logistically during social gatherings, and the guidelines about what can be eaten are hard for some people to follow long term.

5. The 5:2 Diet (Fast Diet)

If you are looking for the simplest way possible to coast into intermittent fasting, the 5:2 diet plan might be the best option for you.

Popularized by the British doctor Michael Mosley, the 5:2 diet allows you to eat normally for five days out of the week, and to eat only 500-600 calories on two non consecutive days.

Sometimes called the Fast Diet, this variation is currently the most popular intermittent fasting diet.

Can't keep it together every single day? Some diets offer a cheat day, but it can be too easy to go off the rails for some people.

Can't keep it together every single day? Some diets offer a cheat day, but it can be too easy to go off the rails for some people.

There are no eating requirements besides counting calories two days a week, and you have complete control over which days those will be. Many people chose to fast Monday and Thursday and eat regularly for the rest of the week.

Because it can be easy to overindulge on regular eating days, followers of the plan that want to lose weight will need to be mindful to keep their eating within a healthy range.

  • Advantages: This plan is easy to follow, has minimal instructions, and allows you to eat whatever you want five days out of the week. There also aren't any times when food is completely restricted, making it an easier eating plan to fit into your social life.
  • Disadvantages: This meal plan can be so similar to regular eating that some people won't notice any positive health effects from trying it.

6. Fat Loss Forever

If you're a gym rat looking to gain lean muscle and you love the sound of cheat days, the Fat Loss Forever fasting plan might be a great option for you. Started by John Romaniello and Dan Go, this plan takes the best parts of Eat-Stop-Eat, The Warrior Diet and Leangains all into one plan.

By far the most complex plan to follow, Fat Loss Forever starts you off with one cheat day every week, which is followed by a 36 hour fast.

The rest of the week is split into varying intervals of fasting and eating periods.

Romaniello and Go recommend that your longest fasts take place on your busiest days, and that you keep yourself busy and productive to keep your mind off your hunger.

When combined with strength training, this plan will bring your to your ideal weight in a very efficient way.

Avocado funny picture
  • Because you will be fasting almost every day, your body gets the maximum benefits from the process, all while getting to enjoy a cheat day.
  • Some people take their cheat day too far and have difficultly losing weight long term. This meal plan is also very specific about when you can and can't eat, making it confusing to follow at first.

3 Health Benefits Of Intermittent Fasting

Regulating your eating through fasting can have lots of health benefits for both your brain and body. Not only can it cause weight loss, it can also help protect you against inflammation and cancer.

1. Weight Loss

Most people find it counter intuitive that intermittent fasting can actually help them lose weight. After all, haven't we been told all our lives how important it is to eat breakfast everyday?

However, the scientific evidence just doesn't follow this evidence well enough to be conclusive.

cartoon exercise

Not only is there not much evidence to prove that breakfast is the healthiest meal of the day, there also isn't any reason to think that eating frequently will boost up your metabolism.

In fact, the evidence seems to point in the other direction.

Studies have shown that IF has the potential to be a powerful weight loss tool.

A 2014 study found that a weekly fasting practice led to 3%-8% weight loss in participants after several months.

Those same participants saw their waist size shrink 4-7%, meaning belly fat was the main type of weight they were losing.

The diet was also found to do a good job of lowering insulin levels and improving the body's ability to process insulin quickly.

2. Inflammation

Chronic inflammation is the precursor to a variety of horrible long term health conditions like arthritis and heart disease. Thankfully, fasting seems to provide some benefit.

Going through periods of fasting can trigger damage-repairing adaptions into your cells, which breaks down inflammation at its beginning.

Numerous studies have shown that regular fasting can reduce the overall amount of inflammation you experience, which helps to lower your risk of developing a disease.

3. Cancer

There hasn't been enough research on the benefits of fasting for cancer for the results to be conclusive, but the early results have been promising.

A study of 10 cancer patients revealed that the harmful effects of chemotherapy could be reduced when patients fasted before getting treatment, while a separate study found that alternate day fasting during treatment led to better cure rates for patients.

While these studies were small and haven't been validated through farther testing, they are encouraging and show the potential that fasting may have for cancer patients everywhere.

Is Intermittent Fasting Safe?

At this point, you may be thinking that fasting looks like a miracle diet cure for everyone. Though the evidence can be compelling, that's not quite true.

There is some evidence that IF might not be a beneficial for women as it is for men.

Some studies have shown that while IF can improve insulin sensitivity levels for men, it can actually have the opposite effect for women and worsen their control of their blood sugar levels.

Regular fasting often stops a woman's period, though it usually comes right back when they stop fasting.

Weight loss funny picture

The practice can also be damaging for women that are trying to get pregnant, are already pregnant, or who are breastfeeding.

If you are female, the best way for you to start intermittent fasting is to ease into it. Start for a few hours at a time and up the amount weekly if you continue to feel good. If you start to notice negative side effects from fasting, you should stop the practice right away.

There are also medical conditions that can make fasting a bad idea. If you have diabetes ore need to regulate your blood sugar, it's not a good idea to force your body to go for hours without food.

Likewise, if you are prone to eating disorders or are already close to being underweight, fasting won't give you much benefit and might even trigger to you start an eating disorder.

It's important that you look at your health history and decide if the benefits of IF are worth the health risks for your specific situation.

All this to say, intermittent fasting is a safe and effective dieting method for a huge number of people.

If you are healthy and well nourished overall, you shouldn't have any problems. However, if any of the following situations describes you, it's best to consult with your doctor before starting IF to be sure you are doing what's right for your body.

You should reconsider starting intermittent fasting if you:

  • Need to regulate your blood sugar
  • Have diabetes
  • Have low blood pressure
  • Are underweight
  • Have a history of eating disorders
  • Are a female who wants to become pregnant
  • Are pregnant or breastfeeding

When Should You Stop?

When you first start fasting, it's more than likely you will experience feelings of overwhelming hunger and feel weaker and slower than usual. This is completely normal and part of your body's adjustment period. Your feelings of hunger should fade within a few fasting sessions as you get used to occasional hunger pangs.

For the first few times, you can even have a small snack handy just in case you need to revive yourself.

However, if you feel ill or faint every time you start to fast, something bigger might be going on and you should grab something to eat and talk to your doctor right away. Fasting isn't for everyone, and some bodies respond differently than others.

Some people truly do need to eat three big meals everyday, and that's perfectly fine. The best thing you can do is listen to your body and adjust your fasting plans according to what it responds best to.

Effects On Exercise

Woman practicing yoga

What are the effects of exercising while fasting?

Intermittent fasting can have positive effects on your exercise and strength training regimes. Unlike other diets, intermittent fasting causes you to lose less muscle mass, and the it becomes more effective when paired with endurance exercise.

Training while fasting can lead to better metabolic efficiency (which leads to better performance) and a higher anabolic response when you eat after exercise. This means your body will be revved up to burn through fat more quickly.

When you work out while you fast, you burn more fat during the workout. Some studies even showed that IF caused 20% more fat to be burned during workouts.

However, every body responds differently and some people find it much harder to work out when they are fasting, and some people need to skip their workouts entirely.

No matter what your fast schedule looks like, it can be a good idea to eat a small snack before working out.

Effects on Muscle Loss

It's a common concern that fasting causes muscle loss. In most cases, these beliefs are unfounded.

Though health supplement companies want you to think your body will fall apart if you don't eat protein every couple hours, the truth is quite different.

Minions weight loss funny picture

The human body is an expert at preserving muscle mass while fasting and protein absorbion takes hours to complete.

Though muscle loss will eventually start to occur from fasting, it won't start until you have been doing it 72-96 hours, far longer than most people want to give up food!

Paradoxically, your metabolic rate actually goes up during short term fasting.

Not eating triggers the hormones epinephrine and norepinephrine, which sharpen the mind and make us want to move around - just like an early hunter getting motivated to seek out his next meal. In the short term, this response will help you to lose more weight.

Taking Supplements While Fasting

Lots of people are unsure whether they can continue to take health supplements when they are on a fast.

Supplements can be a healthy part of your diet and can be a great way to supplement a fast with some of the vitamins and nutrients that your diet might be missing.

However, pay attention to whether your supplements can be taken on an empty stomach.

Most vitamins are recommended to be eaten with food, because the side effects of eating them on an empty stomach include nausea, diarrhea and stomach pain. Keep yourself feeling comfortable by reading the bottle first and adjusting your consumption accordingly.

Tips For Your First Fast

Sunset and a glass of water

Water is one of the most important factors in a successful and healthy fast.

Ready to give fasting a try? Here are some tips to keep in mind

  • Change how you think: Your fasting needs to be thought of as a break from eating, not a period of deprivation. Don't let yourself worry about what you'll eat when and instead just let yourself be in the process.
  • Drink lots of water: Being dehydrated makes every fast more difficult to get through, so keep a water bottle by your side where ever you go.
  • Fast overnight: By keeping your longest fasts during the night, you allow yourself to sleep through eight hours of it, which makes the process much easier mentally.
  • Go all in: At least with your schedule, that is. By keeping yourself busy you don't have time to think about your hunger.
  • Go for a workout: Working out during your fast helps you to burn fat faster, which makes your fasting plan even more effective for weight loss.
  • Keep your expectations realistic: Intermittent fasting can be a great weight loss tool, but it's not going to solve all your problems. Instead, think of it as one part of a larger plan to get fit and in shape.

In Summary

When followed properly, intermittent fasting (along with portion control) can be a great weight loss strategy for almost anyone.

If you are tired from following traditional diets and want to make a change to lose those last few pounds, intermittent dieting can be a way to become healthier, lighter, less prone to disease, and even more muscular and physically fit.

Take the time to try out different methods and intervals of dieting, and you will soon be enjoying the benefits of this simplified eating strategy that have been helping people to live longer, healthier lives for thousands of years.

Have you had experience with intermittent fasting? What was your impression of it?

We want to hear from you!

About the author


I’m a personal fitness trainer and nutritionist living in sunny Indianapolis, IN. I’ve spent the last 8 years staying at the forefront of the health and fitness industry. In that time, I’ve helped hundreds of people shed the excess weight and get into shape, maintaining their healthy new lifestyle through proper training and eating habits.