How Long Does it Take for 16/8 Intermittent Fasting to Work?

Table of Contents

What is 16/8 Intermittent Fasting?

In this method of fasting you eat during an 8 hour window and fast for 16 hours. Ideally you include sleeping time which makes this style of fasting a lot easier to manage.

Advantages of 16/8 Fasting

As your meals are contained in an 8 hour window the advantages are mainly psychological. If you start your eating window at 10am then it’s not too hard to wait for 3 hours after you wake up at 7am.

And if your window then ends at 6pm then you also won’t go to bed hungry.

The 16:8 fasting schedule is one of the easiest regimes to stick to because it fits into your lifestyle easily!

Example 16/8 Fasting Schedule

Wake up and have a beverage such as black coffee or tea (no milk or sugar). Or choose any other zero calorie drink (this helps to suppress morning hunger).
Your first meal should be timed to be 8 hours before your last meal is planned. If you plan on finishing at 6pm then you can start eating at 10am.

More examples of 16/8 schedules:

If your last meal is 8pm then you can start eating at noon.
If dinner is at 5pm then you start your eating window at 9am.
If you eat late at 9pm then your first meal would be at 1pm.

What Should you Eat on this Regime?

The beauty of fasting is that you can eat (almost) anything! However, you should aim for nutritious, whole foods.

A simple rule I use is “anything you could have caught or harvested with a sharp stick in the jungle”. That means lots of nutritious fruits and vegetables, along with a source of whole food protein. Ideally the latter is grass fed beef or lamb. If it’s pork or chicken then free range animals with higher welfare aren’t only better for the animal, they’re better for your health!

What You Should Not Eat During a Fast

During the 16 hour fasting window you should not eat anything with calorific value.

If you feel hunger creeping in then indulge in some black tea, coffee, sparkling water, plain water etc. Or to really mix it up throw some lemon or lime into your water! Anything with calorific value is strictly forbidden as even a small amount can break the effect of a fast.

How Long Does It Take for 16/8 Intermittent Fasting to Work?

How long fasting takes depends entirely on your goals. Let’s break this down into different goal oriented groups:

Bodybuilders

If you’re looking to lose fat and retain muscle then you should place yourself onto this group. According to a study from 2016, 8 weeks of 16/8 fasting in bodybuilders produced the following results:

No loss in fat free muscle mass (retained their gains)
A significant reduction in body fat
No loss in strength

The study notes that participants continued to train during the 8 weeks spent fasting, which was likely crucial to retaining strength and muscle mass.

The subjects averaged 84kg in body weight with a fat mass of around 11kg. Hence these results are fantastic if you want to retain your muscle mass and lose fat (everyone’s dream!).

Weight Loss

Once of the primary reasons for doing an intermittent fast is to lose weight. To see if this works we can look to a systematic review and meta analysis available for free on PubMed.

In the analysis they included 8 RCTs (randomised control trials). This may seem like a low number but they started with over 3,000 studies most of which were found to be very low quality!

The results of the analysis showed that Time Restricted Eating (scientific name for 16:8 fasting) showed benefits in retaining muscle mass and reducing body fat. In particular the average weight loss was just over 1kg of body fat over periods of 4 – 12 weeks fasting.

1kg of body fat may sound low but it’s actually fantastic when you consider that little to no muscle mass was lost at the same time. That’s not something that other fat loss regimes can boast.

Additionally, this way of fasting is very, very easy to implement, requiring only a subtle change in your meal timing and tiny bit of abstinence in the mornings.

The studies also showed better glucose metabolism, a bonus coming from fasting this way.