Intermittent Fasting: The Complete Guide

If you’ve ever heard fitness experts discuss intermittent fasting, then you know things can get… intense. Everybody is skeptical of “miracle diets,” because we’ve all been burned before. 

I feel your pain. I spent years believing my fitness hinged on me eating six meals a day.

All that changed when I learned about intermittent fasting, and here’s why:

Intermittent fasting is not a miracle diet. In fact, it’s not even a diet really.

There’s nothing magical about it. It doesn’t trick your body into burning an unnatural amount of fat. You won’t “lose 10 pounds in 10 days” with IF. You will, however, have a sustainable meal plan that lets you hit whatever your fitness goals are. As James Clear explains:

“Intermittent fasting doesn’t change what you eat. It changes when you eat.”

That’s all IF is. It’s an eating schedule that allows you to eat real meals—not lemon juice and diet pills—while still hitting your caloric goals.

We’re going to look at what IF is all about, examine how it works, and show you how you can get started with IF today.

Let’s start with the basics.

What is Intermittent Fasting?
Here’s how Brad Pilon defined the term “fasting” in his outstanding book Eat Stop Eat:

“Fasting is the act of willingly abstaining from some or all food and, in some cases, drink for a period of time. Willing is the key word here that differentiates fasting from starving.”

Intermittent fasting simply involves splitting your day into two windows:

A fasting window (16-24 hours, depending on plan) during which you don’t eat.

A shorter feeding window (8-24 hours, depending on plan) during which you eat.

Fasting has been practiced by religious groups and prescribed by medical practitioners for centuries because of its various health benefits.

Pervasive advertising from the food industry is the reason this ancient practice is just now getting the mainstream attention it deserves.

Here are some of the lies this $200 billion industry has fed you about fasting:

Fasting deprives your body of nutrients.

Fasting does nothing to modify your dietary habits.

The weight loss that comes from fasting comes entirely from muscle.

When it comes to fasting, can you really trust the words of an industry whose bottom line would be negatively affected if everyone stopped eating as frequently?

Out of these lies arose the old bodybuilding myth that you had to eat several small meals during the day to feed your muscles protein or else they’d slowly wither away.

Turns out our muscles don’t need as much protein as we’ve been led to believe.

How Does Intermittent Fasting Work?
The law of energy balance is foundational to any nutrition plan, but it’s especially important here since IF is merely a way to maintain proper energy balance.

There are two core truths this law teaches us:

The only way to shed body fat is to consume fewer calories than you burn.

Consequently, a prolonged caloric deficit is the only path to long-term fat loss.

IF helps you manage this prolonged caloric deficit because, quite frankly, eating fewer sucks.

[Source: Authority Nutrition]

We all love to eat because food is delicious and wonderful. The good news about IF is that you get to eat what you want as long it works within your calorie budget.

Scientifically speaking, IF works because our bodies naturally exist in either a fed state where calories are being stored, or a fasted state where calories are being burned.

After you eat, your body enters a fed state and starts breaking down the food you just ate.

Since the energy from that food is immediately available in your bloodstream, your body won’t tap into your fat storage for energy, thus leaving your level of stored fats unchanged.

Ten to 12 hours after your last meal, your body has finally broken down the food you ate.

Once this happens, your body enters a fasted state. With no food energy available, the only source of energy your body can tap into in this state are your fat cells.

Let’s take this one step further. Guess what happens when you work out in a fasted state?

That’s right: Your fat cells get absolutely torched.

Why Should I Try Intermittent Fasting?
Now’s a good time to reiterate that intermittent fasting is not the holy grail of fitness, but rather a tool in your fitness repertoire to help you maintain a caloric restriction.

Fitness bros love to twist the results of IF studies to make you believe that fasting can reduce inflammation, curb your appetite, and even cure cancer.

These benefits, which we’ll discuss below, have not been proven. You should take every new discovery with a grain of salt when it comes to intermittent fasting.

What you can take to the bank, on the other hand, are three major lifestyle benefits of IF that give it a huge advantage over whatever dieting plans you might have tried.

Benefit 1: You Get Immediate Results If You’re Leaning Out
If you haven’t done IF before, your body will be in shock during that first week as it adjusts to you not eating at your regular times. I won’t lie to you: It’s pretty miserable.

The good news is that you’ll see immediate results within the first week.

When I started IF five years ago, I remember looking and feeling significantly leaner that first week. I still had hunger pains, but seeing my body lean out so quickly got me through it.

Benefit 2: You Don’t Have to Stress Out About Meal Prep
If you’re like me and bought into the bodybuilding myth that you have to eat six meals a day in order to feed your muscles, you know what a pain in the ass meal prep can be.

Intermittent fasting gives you back all those hours you spent cutting up chicken breasts and washing the Tupperware you took to work.

For all the wives and girlfriends out there who handle meal prep—like mine used to do—IF is one of the best gifts your partner can give you. The days of silent resentment are over!

Another time-saving element of IF: You don’t have to agonize over what to eat for breakfast.

Benefit 3: When You Eat, You Can Eat Big
When you’re eating six times a day, every meal is 300-400 calories. I found myself frustrated by this regimen because each meal was over before it ever really got started.

Advocates of this method out that you never feel hungry because you’re eating all day.

I’m calling bullshit on that notion—I never felt full, so I was hungry all the time.

With IF, I get to eat two large meals a day and go to bed stuffed. It’s wonderful.

By shifting all my calories to lunch and dinner, I have about 1,000 calories per meal. That means I get to eat what I want, plus I save time by eating two meals instead of six.

These three lifestyle benefits are not the only perks of IF. Since we’re changing when we eat and not what we eat, you can shift your fasting window to include your favorite meal.

If you can’t live without breakfast, make that your first meal. If you eat lunch and dinner, you can always indulge every once in a while and eat breakfast on vacation like I do. Don’t worry, your progress won’t unravel.

The Drawbacks of IF
Now that we’ve talked about the benefits, let’s discuss some drawbacks of IF.

The first drawback is that the effects on women are mixed. Women are different hormonally from men and some women don’t cope well with IF because of these differences.

That’s not to say women can’t find success using IF, just that their results will vary from the steadier, easier-to-anticipate results of their male counterparts.

The second drawback is that the initial transition is quite difficult.

How difficult depends on the individual—I’ve coached some clients who said it was a breeze and had others who counted the minutes until lunch like an inmate getting out of jail.

[Source: LiveScience]

Your body only needs one or two weeks to adjust to your new eating schedule. Once you get over that hump, you’ll no longer feel hungry during whatever mealtime you’re skipping.

One downside people tend to stress about is how skipping meals will affect their blood sugar levels. Won’t they pass out if they skip breakfast and their blood sugar plummets?

No, you won’t. Research shows it takes more than skipping a particular meal to pass out.

Another misconception is that fasting causes muscle loss because you aren’t feeding your body the protein it needs. That’s why I believed you had to eat six small meals per day.

This is a lie developed by the multibillion-dollar supplement industry. You don’t need protein every 2-3 hours like they say you do, which means fasting won’t cause muscle loss.


When Can I Eat with Intermittent Fasting?
We know the basic premise of IF is that your day is split into a fasting window and a feeding window, with the fasting window lasting longer than the feeding window.

Within that basic framework are four popular protocols for scheduling your meals.

Let’s start with the most popular protocol, which happens to be the one I use.

Leangains (16:8)
Leangains, or 16:8 as it’s known in fitness parlance, was popularized by Martin Berkhan, the man I consider to be the godfather of incorporating IF within a strength training regime.

The 16:8 protocol is simple to understand:

Your fasting window is 16 hours.

Your feeding window is 8 hours.

You can shift your fasting window around to suit your needs, but if you’re like me and you have a family, you’re better off skipping breakfast than you are skipping dinner.

I find it hard to fall asleep on an empty stomach, plus I don’t want to skip dinner with my family.

That said, if you’re in a job where breakfast meetings are common or you just can’t live without your morning bagel, you can shift your window to include breakfast at the expense of dinner.

You can’t have both breakfast and dinner at 16:8. You have to choose one.

Here’s how your day will look with 16:8 depending on which meals you include:

If you’re skipping breakfast, your feeding window is noon to 8:00 p.m.

If you’re skipping dinner, your feeding window is 8 a.m. to 4 p.m.

Again, you can tweak the start times to meet your needs, but this a rough guideline.

During the fasting window, you can’t consume more than 10 calories.

Within that feeding window, you can have as many meals as you want as long as you observe your caloric restriction, but like we covered earlier, eating more meals per day is difficult.

For that reason, I recommend two meals during your feeding window: lunch and dinner.

Having multiple meals or snacking makes it harder to track what you’re eating.

Eat Stop Eat (5:2)
The second IF protocol comes from the book Eat Stop Eat by Brad Pilon. Even if you don’t use Brad’s protocol, I recommend reading his book for the insight you’ll gain on IF.

His approach is a little different than Leangains:

2 days a week, you fast for 24 hours.

5 day a week, you eat normally.

Speaking from experience, a 24-hour fast is really difficult but not impossible.

I use this protocol strategically for times like Thanksgiving where a big dinner awaits me.

To make it more manageable, I eat dinner the night before the event and then fast for 24 hours until the big dinner the next night. That way I’m not skipping an entire day of meals.

I don’t use this protocol on a regular basis because the last four hours of the fast are brutal. Since I skip breakfast, I can stretch a fast to 2 p.m., but after that I’m struggling.

You might have no problem fasting 24 hours, and if so, God bless you.

The Warrior Diet (20:4)
The third IF protocol is the Warrior Diet by Ori Hofmekler.

This protocol is similar to Leangains with one notable exceptional:

Your fasting window is 20 hours.

Your feeding window is 4 hours.

Ori dubbed it the Warrior Diet based on the nutritional habits of ancient warriors who were out to battle all day long and came back to camp at night for dinner, their one meal of the day.

The Warrior Diet is looser with its caloric restriction during the fasting window, allowing light calorie consumption through a small meal or fruit.

I’ve never tried his method, so I can’t speak to its effectiveness.

Alternate Day Fasting (ADF)
The last IF protocol is called alternate day fasting, or ADF. I’ve also heard it referred to as the UpDayDownDay Diet, and it’s the creation of Dr. James Johnson.

This one is self-explanatory: You have a 24-hour fast followed by 24 hours of not fasting.

Similar to Eat Stop Eat, you can eat whenever you want on days you’re not fasting.

I’m not sure why you’d choose to fast 3-4 days a week when Eat Stop Eat only requires 2 days of fasting, but some people use this protocol, so I wanted to share it.

How To Get The Most Out Of Any Intermittent Fasting Protocol
Whichever protocol you choose, your calorie intake is severely restricted during the fasting window. Making it through that time, especially at first, can feel downright impossible.

During your fasting window, if you find yourself dreaming of pounding double cheeseburgers in Wendy’s parking lot, employ these strategies to help get you through:

Drink black coffee. You can add a splash of skim milk if you need it.

Sparkling water or diet soda can also help blunt your appetite.

If you need to chew something, chew a piece of sugar-free gum.

My biggest piece of advice is to stay busy during the mornings (or nights, if you’re skipping dinner). Being on 16:8, mornings are my most productive time of the day.

Does it annoy me when there are donuts in the office and my coworkers are all having a great time eating them and I’m stuck staring at my computer screen?

You bet your ass it does. I secretly hope they all choke. (I’m mostly kidding.)

But you know what? I deal with it because I know IF has totally changed my life.

Up until 2011, I just assumed everyone who managed their diet was miserable like me.

I was highly skeptical of IF at first because I’d been brainwashed by every fitness book, blog, and magazine into thinking I needed six meals a day to maintain my metabolism.

As I researched IF, the words “starvation mode” kept popping to mind. If I didn’t eat every 2-3 hours, I feared my body would enter start feasting on my muscles.

Eventually, I got fed up with stressing over meals and not seeing the results I wanted.

Despite my skepticism, I took the plunge and gave IF a shot. Now, five years later, I no longer stress about meal planning and enjoy the freedom to eat what I want.

I can’t promise it will cure cancer, but I know from experience that intermittent fasting is the protocol you need to get your diet under control and take your fitness to the next level.

When You Hear Hype, Remember the Truth About IF
As intermittent fasting continues to gain popularity, you’re going to hear a lot of hype about miracle benefits that some new “study” has supposedly proven:

Growth hormone, which you need to lose fat and gain muscle, increases after fasting.

Fasting reduces inflammation and helps with appetite control.

IF extends your lifespan and reduces the risk of cancer and cardiovascular disease.

These unproven benefits would be nice added bonuses, but they’re ultimately a distraction.

Regardless of whether IF cures cancer or helps your muscles grow, it is simply the best, most reliable way to schedule your meals and maintain your caloric deficit.

Consult a doctor before beginning any type of intermittent fasting protocol.

Author Bio: Jay Kim a full-time desk jockey and fitness hacker. He works with world-class athletes and other high performers to help them achieve the fitness results they need and shares his methods at