What Is Intermittent Fasting? A Beginner’s Guide to Burning More Fat

Want to burn more fat without changing what you eat? Intermittent fasting isn’t a diet. Intermittent fasting is just a different way of eating.

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BY Jeff Haden - 10 Aug 2017

PHOTO CREDIT: Getty Images

For over a year I've been following an intermittent fasting eating regimen. I use the word "regimen" because intermittent fasting is not a diet, at least in a "consume less calories" way. Intermittent fasting is all about when you eat, not what you eat.

Even though I'm usually up by 4.30 or 5 a.m., I don't eat anything until 10.30 a.m. I space out my meals for the next 8 hours and quit eating for the day at 6.30 p.m. For the next 16 hours I fast (hence "intermittent fasting") and then start the process all over again the next day.

Again, intermittent fasting is not a diet (although you can follow an intermittent fasting schedule in conjunction with a calorie reduction plan.) It's just a different way of eating. In fact I'm trying to gain weight -- lean weight -- so within that 8-hour window I typically take in 200-300 more calories than I burn.

So why restrict myself to that 8-hour eating window? Intermittent fasting is a great way to burn more fat. Intermittent fasting is a great way to change your body composition and shift your muscle:fat ratio towards a greater percentage of muscle. Since I've been intermittent fasting I've gained almost 7 pounds and decreased my body fat by 4%.

Yep: I've gained weight yet also lost fat.

Let's look at how that happens.

The Science Behind Intermittent Fasting

Think of your body as being in two states: the "fed" state and the "fasted" state.

The fed state occurs when you're digesting and processing food. Start eating and your body shifts into the fed state. Even after you've finished eating you stay in the fed state for roughly 3 to 5 hours (depending on what you've eaten, how frequently you've eaten, your metabolic rate, and other factors.)

When you're in the fed state your insulin levels naturally increase, and when your insulin levels are high you typically don't burn fat for energy. Your body doesn't need to tap into its fat stores because what you're eating gives it plenty to work with.

Somewhere between three and five hours your body stops processing its last meal. There's nothing left to absorb, insulin levels naturally decrease, and somewhere between 8 and 12 hours after that last meal, your body starts burning stored fat. (Why don't you start burning fat sooner, you ask? Biology is sometimes a pain in the ass; it's like our bodies will do anything to hang on to fat. )

In short, when you're in the fed state your body doesn't need to burn fat; it's like the door to the fat store is locked. When you're in the fasted state, the door to the fat store swings open.

But it takes 8 to 12 hours to get into the fasted state. Start your day with breakfast at 7 a.m. and don't have your last meal until your 9 p.m. snack and you almost never go into a fasted state. Fast for 16 hours and you do.

And that's how, over time, you can lose a few percentage points of fat even if you don't change your exercise routine and don't change what you eat; keep all the other variables consistent and intermittent fasting will cause you to lose fat.

Science says so; in one study, after eight weeks participants who followed an intermittent fasting eating schedule lost 3.5 pounds of fat while those who exercised the same and took in the same total calories did not.

In another study, participants reduced their waist circumference by 4 to 7 percent. Other studies have shown that fasting can reduce the risk of cardiovascular disease and cancer.

Plus who can ignore Jackman science; to play Wolverine, Hugh followed an intermittent fasting eating regimen to put on 25-30 pounds of muscle while also leaning out.

Yep: Intermittent fasting works.

How to Create Your Intermittent Fasting Plan

The beauty of intermittent fasting is that there really is just one rule: Eat for 8 hours, don't eat for 16 hours. (Some women choose to fast for 18 hours; try it if you want, but jeez that's a long time to go without eating.) When you decide to start eating is up to you. What you eat during that time frame is up to you.

Figure out what works best for your schedule and your lifestyle.

Most people wait a while after they wake up to stat eating; for me it's easier to hold off for a few hours in the morning than it is to go, say, from 3 or 4 p.m. until bedtime without eating. Plus, if you work out in the morning before you eat, you get to double-dip on fat burning since your body will use even more of your stored fat for energy.

For most people, that means eating fewer times during the day; before I started intermittent fasting I was eating 6 or 7 small meals each day. If you're not trying to lose weight you may have to eat a little more than normal at each meal. (If you are trying to lose weight, intermittent fasting may help you consume less calories simply because your "eating window" is smaller. Win-win.)

At first it won't be easy to switch over to a new eating regimen, so consider easing into it. Start out on a M-W-F plan, intermittently fasting on Monday, Wednesday, and Friday, and eating normally the other days. After a couple weeks, add in another intermittent fasting day, then another...

And keep in mind you don't have to go all-in on intermittent fasting. Dick Costolo, ex-Twitter CEO, takes Sundays off. Other people take a day off every two weeks or so. Some never go past a M-W-F schedule. Research shows that some of the benefits of intermittent fasting still result from a more limited approach.

But whatever you do, create a plan and stick to that plan. Don't fast when you feel like it. Make a plan and follow your plan. But you don't have to be a slave to it; if you fall off the intermittent fasting wagon one day, just jump back on the next day.

If you do your best but can "only" stick to your plan 95% of the time, don't beat yourself up. 95% is great -- and so are the benefits you'll see.

Remember, life isn't all or nothing -- and intermittent fasting definitely isn't all or nothing.

Want more info?

The 8-Hour Diet is a good intro to intermittent fasting.

So is Intermittent Fasting for Women.

And so is Eat Stop Eat.

Here's a good video primer by Dr. Eric Berg.

And another by the Lean Gains folks.

And Dr. Berg on how to make intermittent fasting work faster.

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