Intermittent Fasting 20/4 vs 16/8: What’s the Difference?

When it comes to intermittent fasting, there are many different eating protocols on offer. 20/4, 16/8, OMAD (One Meal a Day) and more. If only having one meal a day sounds a bit much for you, then you may be considering intermittent fasting 20/4 vs 16/8. Does one protocol rule over the other?

Ultimately, it’s personal preference. But there are some significant differences that might be the deciding factor for you. Here we will discuss the differences and leave the decision making up to you.

What is Intermittent Fasting?

If you’ve just given this a google then it’s likely that you already understand what intermittent fasting is, but on the off chance you don’t here’s a quick overview. 

Intermittent fasting is a diet which restricts how long in a day you have to eat instead of simply restricting the exact food or calories you can choose from.

Traditional diets such as keto restrict whole macronutrients such as carbohydrates from your eating habit. Calorie counting restricts how much food you can eat in a day.

Neither of these rules come into play with IF.

Instead you simply have less time in a day to eat. The overall aim is a reduction in body fat, however there are additional purported benefits from reducing the amount of time you have to eat in the day, such as greater use of fat as a fuel source, better management of type 2 diabetes and purported cognitive benefits.

You might also like: Can I Do Intermittent Fasting Without Exercise?

20/4 vs 16/8, What Gives?

Intermittent fasting 20/4 vs 16/8 are two different types of eating windows.

The first number is the amount of time in the day you are not allowed to eat, the second number dictates the amount of time in a day you can eat.

20 hours of not eating, vs a 4 hour eating window. And 16 hours of not eating vs an 8 hour eating window. You may be thinking that the differences stop there, but not quite. 

20/4 Intermittent Fasting

The 20/4 eating window was allegedly popularized by writer Ori Hofmekler in 2001.

His eating protocol was also called The Warrior Diet, claiming it was the same eating habits as ancient warriors.

The idea behind it is you fast throughout the day and then give yourself permission to eat whatever and however much you like in a 4 hour window. Essential feasting in celebration of your successes as a warrior. 

Many people have seen success during this diet as the relatively short eating window ensures that you are unable to feast for too long.

Abstaining from food all day to then suddenly eating can cause high satiety and an inability to eat too much in such a short amount of time.

However, this is not always the case and as with any IF protocol fat loss is not guaranteed. 

Such an overly restrictive diet is not sustainable for many people. And as dieting is often temporary for most people, managing the transition to regular eating can be a challenge and can result in the risk of regaining any body fat lost during the process. 

16/8 Intermittent Fasting

The high difficulty of intermittent fasting 20/4 may mean that you would be better off considering intermittent fasting 16/8 instead.

As you may have inferred from the name, this protocol allows for a much bigger eating window. In fact, one that’s perhaps more manageable due to its similarities to everyday eating.

An 8 hour eating window allows for more regular meals to be eaten. On a typical day people tend to break up their breakfast, lunch and dinner across a 12 hour period from 7am to 7pm.

Simply skipping breakfast, like most people do, and starting the day with lunch will put you in that 8 hour eating window. Which, for most people, is a nice transition into the practice of intermittent fasting. 

Allowing yourself 2 meals a day and all the benefits of an IF protocol.

In contrast to 20/4 this allows for much more freedom in your food choices and doesn’t restrict you from joining friends and family in social eating events like a team lunch or family dinner. 

So Which Is Better For Fat Loss? 20/4 or 16/8?

From a scientific standpoint, specifically with how both intermittent fasting protocols affect the fat burning process itself, there are some interesting considerations. 

Briefly, it’s important to remember that fat loss and fat burning are not one and the same thing.

Fat loss is what happens when the body is in a consistent caloric deficit, and the body turns to its stored calories (body fat) to provide that additional needed energy. This is how one loses fat.

Fat burning is in reference to the process of the body converting fat into ATP, the body’s energy currency, when performing activities. It’s an inefficient source of energy and is mostly used during periods of low intensity like sitting or ambling around the house. When intensity increases, the body turns to glycogen or creatine until it runs out of both and then turns to fat once more to keep you active. 

The body using fat for fuel does not guarantee body fat loss if caloric intake is still at or above maintenance. 

All intermittent fasting protocols yield the same benefit of making you more efficient at using body and dietary fat for fuel due to the restive eating windows reducing the bodies intake of carbohydrates.

Similarly to ketogenic diets this will cause the body to rely mostly on fat for energy, producing ketones intermittently and assisting with insulin sensitivity by reducing the amount of glucose in the blood stream. 

All benefits seem to be shared between the two different eating protocols, with little to no additional difference being found. 

The overall benefit of IF is being able to put yourself in a caloric deficit, the only way to lose body fat, without having to laboriously count calories every single meal.

And whilst IF doesn’t guarantee fat loss, the reduced meal frequency certainly helps.

Bottom Line

It is not difficult for any person to see results when comparing intermittent fasting 20/4 and 16/8. And it could be fair to say that one will yield quicker results, 20/4, than the other, 16/8. 

However, that being said, fast fat loss is not always a positive thing. And what’s lost quickly is often put back on just as quick due to the overly restrictive nature of the process.

Because of that if you are comparing 20/4 vs 16/8 it might be wise to consider starting with 16/8 and simply skipping breakfast instead of going straight into 20/4 and risking falling off the wagon and binging because you were so hungry.

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Mike Julom, ACE CPT

Mike is an ACE Certified PT and a CrossFit Level 1 Trainer. He is an avid lover of all sports. Basketball, tennis, athletics, volleyball, soccer, squash, golf, table tennis, even darts, you name it! He's a very active CrossFit athlete and has been WOD'ing for over 7 years. With such an intense fitness regime, Mike has learned to take care of his body physically, nutritionally, and spiritually. Mike founded ThisIsWhyImFit as a way to share his vast knowledge of exercises, diets, and general fitness advice.

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