Last updated:

25 July 2023

Intermittent fasting is one of the best ways to improve weight loss results, Here’s how it works.

how to do intermittent fasting to lose weight

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12 min read

Bodybuilders have been using intermittent fasting for decades, and it’s one of the most popular ways to lose weight in 2021.

But it’s also one of the most misunderstood.

Because much like keto, it has been hijacked in recent years by cult-like motherf**kers who throw around words like ‘biohacking’ and call food ‘fuel’.

Catching on trend has seen many of its benefits become misinterpreted and greatly over-hyped but, in a nutshell, it’s really easy to apply IF and get results.

I’ll show you how to do it in this article.

does intermittent fasting work

So how does intermittent fasting work?

Well, it’s based around the very simple concept of eating your daily calories within a designated feeding window, followed by a longer period where no food is consumed at all.


It’s not strictly a diet in itself, more like a tool you apply to your current diet.

This makes it very versatile, because you can apply IF to any type of nutrition plan (flexible dieting, gluten free, bodybuilding-style clean eating, vegetarian, ketogenic, low carb, etc.).

Another example of its incredible versatility are the time splits which can be used. The three listed below are the most commonly used, but there are no restrictions on what you can or cannot do here. My advice is to use the one which fits your lifestyle the best:

  • 16/8 IF split
  • 14/10 IF split
  • 20/4 IF split

Over the years, I have found that most clients saw the best results with a 16/8 split (a 16 hour fast with an 8 hour feeding window).

So now we know what it is, WHY does intermittent fasting work?

Self-appointed ‘gurus’ will claim all kinds of crazy things, as if intermittent fasting is able to rip a hole in the universe and suck belly fat into the vortex, but in reality it’s much simpler. Calorie control.

If you’re a regular reader of my site, you know that the number 1 ingredient in a successful weight loss diet is sustainability. (1)

By forcing you to eat your daily calories in a much shorter timeframe, there is far less chance you’ll over-eat. That’s where 99.9% of your results will come from, and it needn’t be any more complicated than that.

The other 0.01% comes from the fact that fasting appears to be able to increase the activity of certain genes responsible for how much fat the body can metabolize, enabling us to burn more calories (and more fat) throughout the fasting period itself. Some researchers believe the activity of these genes temporarily spikes even further when we begin our feeding window, causing even greater fat burning. (2, 3, 4, 5)

These benefits definitely do exist, but they’re greatly overblown.

how to do intermittent fasting for weight loss


Like any nutritional tool, some people will LOVE it and some people will HATE it.

However, in my 20 years experience as a personal trainer I’ve noticed that there are 2 groups of people who typically see the BEST RESULTS with intermittent fasting:

  1. People who need more structure in their nutrition plan.
  2. People who have already seen great results and want to break a tough plateau.

Do you identify with either group?

If so, you’ll likely see better results – particularly if you’re in the first group.

If you’ve had a history of struggling with your nutrition, the rigid structure of IF tends to help people break most of the old habits that were holding them back. For instance, as your body gets used to only eating at certain times of the day, the majority of trainees find it easier to avoid those unplanned snacks that used to wreck their diet.

But be warned… the first few days of IF will suck harder than a Nickelback concert.

You’ll feel snappy. You’ll feel hungry. You’ll wonder why you’re doing it. But then you’ll adapt to it and feel totally fine. In fact, many trainees never stop using IF once they’ve got the hang of it.

It’s a technique I also like to use in the last part of a fat loss phase, when it becomes doubly important to stay within your reduced calorie intake. In this instance, a shortened feeding window makes the trainee feel like they’re eating more than they actually are, inceasing the likelihood they’ll stick to their nutrition plan when the going gets tough.

Make sense? Good!

Legendary bodybuilding coach Jim Stoppani is a big fan of intermittent fasting. He had this to say:

Jim Stoppanie intermittent fasting

“I believe in enjoying life, but I’m also passionate about fitness. You know those two pursuits can become extremely difficult to balance!

That’s why I have been following an intermittent fasting eating plan for years now.

It lets me eat the foods I want (within reason, of course!), while maintaining my physique.”

– Jim Stoppani

is intermittent fasting good for weight loss


Certain cultures have been using intermittent fasting for decades, but like anything that catches on trend, it has been bastardized.

Take a look at social media, you’ll see all kinds of crazy advice!

There are even fasting detox plans out there now, from so-called ‘gurus’ looking to make a quick buck. How anyone can class themselves as an expert in not eating is beyond me, but this is the fitness world… where anything is possible!

One myth those ‘gurus’ love to say is that intermittent fasting can reverse the effects of type 2 diabetes.

This is not true.

In fact, a 2015 study published in Diabetes Care found that fasting (in this case, skipping breakfast) actually impaired insulin response. Improving your overall lifestyle and getting regular exercise will reverse the effects of type 2 diabetes, and intermittent fasting can be part of that jigsaw if you want, but is not capable of reversing diabetes on its own. (8)

Another myth is that intermittent fasting can boost oxygen supply to muscles during exercise.

Again, not true.

Early research on this showed a very slight increase, yes, and this created a big buzz around IF because it’s essentially the same thing endurance athletes are trying to achieve when they take illegal substances.

However, fasting doesn’t create anywhere near the same level of improvement. (6)

And now on to my favorite intermittent fasting myth…

I’ve saved the craziest until last.

Yes, there are some ‘gurus’ out there which claim you can eat whatever you want as long as it’s within your feeding window!

Website member Jenny asked about this particular myth on my social media recently:

“Hey Russ!

My friend recently started intermittent fasting, and it sounds too good to be true. She says she can eat whatever she wants as long as it’s between certain times of day?!”

– Jenny, USA

Allow me to put this myth to bed: fasting cannot over-rule the law of thermodynamics. (7)

Misguided coaches give this advice because they believe the shortened feeding window makes it impossible for a person to over-eat. Obviously they’ve never seen my kids on a Saturday night…

A buddy of mine fell for this myth when he discovered intermittent fasting back in 2014. I can still remember him telling me about it at a family barbeque. Some YouTube ‘guru’ claimed he could eat without restriction from 12pm to 8pm…

So he did, and he wound up gaining 30lbs.

Worse still, he’d told all of his friends about this new fat loss ‘secret’ and they’d all gained weight.

So remember, intermittent fasting does not mean intermittent bingeing.

A binge/starve/binge/starve eating style is not only silly (because 8000 calories is still 8000 calories, regardless of the time) it also creates a very unhealthy relationship with food and just makes us want junk food all the time.

For example, at the same family barbeque I dropped a packet of M&M’s on the floor. Best game of Hungry Hippos I’ve ever f**king seen.

intermittent fasting


While researching for this article I opened up the floor to my social media followers to send me their biggest questions regarding IF.

I figured this would be a pretty neat way to wrap up this article.

You can see the best of them below.


There’s a growing landscape of research supporting the use of IF for fat loss purposes, but iresearch on using IF to build muscle is very scarce.

It’s not that it can’t be done, of course.

It’s just that the main strength of IF is calorie restriction, so it’s a technique best applied to weight loss diets. If we’re trying to get bigger we’d want to be eating more calories per day, so limiting your feeding winow isn’t the best idea.


In a perfect world scenario your feeding window begins as soon as your workout ends. You’d get some quality post-workout nutrition, then consume the rest of your calories and help your body recover before the next workout.

However, nobody lives in a perfect world. Most people have jobs, families, and other commitments to think about.

Heck, I have three boys and my house resembles the latest edition of the Royal Rumble every morning. You think I worry about perfectly timing my feeding window after returning from the gym at 7a.m.? F**k no.

Instead, use your common sense.

Think about when you usually feel hungriest. If you’re a night-time eater, trying to fast at night would be a bad idea as temptation would be at it’s highest, so that should be your feeding window instead.

Sometimes (maybe all the time) this may leave you training outside of your feeding window, and that’s okay. Sustainability is more important than post-workout nutrition. That’s a fact.


Make sure you grab some protein near the end of your feeding window.

It’s the most filling macronutrient, so it will keep you feeling fuller for longer into your fast, warding off hunger and making it much easier to stick to. A slow-release form of protein like this would be the best choice.


No you can’t.

Muscle building magazines and supplement companies LOVE advising people to sip on BCAA supplements during their fasting window “to avoid muscle breakdown”. Myprotein do it here.

This is total bulls**t.

First, you needn’t worry about losing muscle because a fasting window isn’t long enough to cause this to happen anyway. Also, BCAAs will break your fast!

This is a commonly made mistake, because BCAA supplement labels claim the product has zero calories. They do actually contain calories, it’s just that current food industry regulations prevent manufacturers from listing them on the label. If I’ve just blown your mind with that information, read this post for more.


Only those which contain zero calories.

Caffeine can be handy (especially in the first few days) but that’s about it.



Some people fast on weekends. Some people fast every other day.

As the name suggests, it can be used, err, intermittently.

Sure, there are IF zealots who swear this is the only way to eat and everything else is wrong, but you get those type of people in every corner of the fitness world (CrossFit, keto, whatever bulls**t Gwyneth Paltrow is selling, etc.). They are wrong.


A fast is a fast. It builds discipline. Don’t looking for ways around it.

I once read an article from a ‘guru’ who claimed you could eat what they called negative calorie foods during a fast, as they burn more calories being digested than they contain, and I probably burned twice the calories laughing at the f**king screen.

Please stop listening to people who are full of s**t.



intermittent fasting


By now you should have a really good idea how intermittent fasting works and how to apply it for best results.

Many of my male and female clients have applied it over the years and experienced great results, but the final decision rests with you.

Is it something that fits your lifestyle? If so, go for it!

If it’s not for you, that’s fine. After all, I’m always telling you guys that the best diet is the one you can stick to!

If you’ve enjoyed my comprehensive guide on how to use intermittent fasting for maximum results, consider becoming a webstite member below. You’ll get killer workout plans straight outta my gym!

Who Is Russ Howe PTI?


Russ has been a personal trainer in the UK since 2002, and provided both training advice and full programs on this website since 2011.

His work has been featured in Men’s Fitness magazine, and the content on this website led to him being voted one of the world’s top 50 fat loss coaches by HuffPost.

Russ’ days are spent coaching men and women in the legendary Powerhouse Gym, and creating new content for the 109,246 followers of his popular free weekly e-mail, which you can join below!


  1. Stewart, T. M., et al. Rigid vs. flexible dieting: association with eating disorder symptoms in nonobese women. Appetite. (2002)
  2. Pilegaard, H., et al. Effect of short-term fasting and refeeding on transcriptional regulation of metabolic genes in human skeletal muscle. Diabetes. (2003)
  3. Hildebrandt, A. L., et al. Exercise attenuates the fasting-induce transcriptional activation of metabolic genes in skeletal muscle. Am J Physiol Metab. (2000)
  4. Mattson, M. P., et al. Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. J Nutr Biochem. (2005)
  5. Trabelsi, K., et al. Effects of Ramadan fasting on biochemical and anthropometric parameters in physically active men. Asian Journal of Sports Medicine. (2011)
  6. Stote, K. S., et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. (2007)
  7. Swinburn B., et al. Increased food energy supply is more than sufficient to explain the US epidemic of obesity. Am J Clin Nutr. (2009)
  8. Jakubowicz, D., et al. Fasting until noon triggers increased postprandial hyperglycemia and impaired insulin response after lunch and dinner in individuals with type 2 diabetes: a randomized clinical trial. Diabetes Care. (2015)


  1. Harvey avatar

    I’ve been doing I.F. for the last two years and lost 20lbs and kept it off. One of the things which put me off is the cultish behavior some I.F. users have, dead right it’s all about calorie control Russ 🙂

  2. Adam avatar

    I’ve really enjoyed doing IF 12/12 split. Makes shift work so much easier!

  3. Gaz avatar

    Started following IF through one of your earlier blogs. That was 2017, still going strong!

  4. Otis avatar

    Loved this. Straight to the point, thanks.

  5. Wendy avatar

    I’m on week five now and loving it.

  6. Carey avatar

    I have been doing 16/8 most days and it works great.

  7. Merah avatar

    Exceрtіonally well written!

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