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Is Intermittent Fasting Magic?!

Intermittent Fasting or IF (particularly the 16:8 protocol – fasting for 16 hours, with an 8-hour eating window) is seen by many to be a superior way to lose body fat (and also build muscle). In this article we’ll discuss just how superior it is, and whether you stand to benefit from trying it out.

Firstly, is IF superior for fat loss in healthy individuals with no underlying conditions? No!

Reducing body fat is achieved through a calorie deficit, and it doesn’t matter if you eat a set number of calories in the space of 8, 10 or 16 hours. If two diets are iso-caloric (ie, have the same number of calories), then both will create the same degree of fat loss, providing they are adhered to. If you haven’t yet had a DEXA scan then you estimate your maintenance calories here. Bodyscan will give you a more accurate result because the scan enables us to use the Katch-McArdle formula which takes lean body mass as its input. If you have particularly low muscle the non-DEXA, weight-based formula could be 200-400 calories above the true figure! This deep-dive DEXA information video explains the advantages of using a DEXA scan to calculate your calories and shows a real-life example.

Where IF stands to benefit some individuals is through improving adherence to the specified calorie intake. Often, when those calories are spread out across the day, the meals are smaller and less satisfying, thus making it more likely you will over-eat. IF allows meals to be larger and consumed within a shorter time-frame, thus increasing your perceived level of ‘fullness’. If you feel full, you are less likely to eat more (providing you listen to your hunger signals!)

If you are someone who has a big appetite, IF could therefore benefit you as the meals can be larger. If you are someone who can stick to a calorie deficit regardless of satiety levels, then IF will not provide any additional benefit.

Secondly, is IF superior for muscle gain? Not necessarily. Whereas fat-loss is all about the calories, muscle growth depends on how good your resistance programme is and by progressively overloading in the gym. In layman’s terms, this means seeing a gradual increase in the weights lifted, or an increase in the number of sets or reps (with a given weight) in the gym over time. You should therefore eat in a way that optimises performance. Perhaps that means eating small meals frequently throughout the day. Perhaps it means training fasted. Everyone is different. The effect that eating windows have on performance is highly individualised, so there is no one-size-fits-all formula. Section 1 of our free muscle-building guide discusses the factors you can’t change that can adversely affect your efforts (eg, age, sex and hormone levels).

A 16-hour fast and an 8-hour eating window may benefit some people’s training, whilst for others it may be detrimental. The best way to establish what works for you is to try out various approaches.  

To sum up, eating in a specific time window is not superior for losing body fat to an unrestricted eating window providing the same number of total calories is consumed. And time-restricted eating has little to do with muscle gain. You should eat in a way that optimises performance (remember, it’s the effectiveness of your resistance regimen that’s key), which is dependent on the individual – that’s you!

Your first scan with Bodyscan will discuss your unique objectives and simplify everything, thanks to your detailed and plain-English interpretation of your results. This will leave you inspired, motivated and well-equipped to achieve your goal. If you have any questions about the scan, search our FAQs or write to us at [email protected]

We have two DEXA scanning clinics in London – Marylebone and the City. Both are easy to get to by public transport; full details on our contact page.

Rob Webster
Bodyscan Consultant

Philip Chant

Kevin Garde

Rob Webster