Intermittent Fasting 101

Intermittent fasting (IF) – going through prolonged periods of intentionally not eating – is an approach to food that has some kind of mystique around it thanks to being so far out of the norm. Common dietary advice has generally centred around eating little and often for decades and so as soon as a person starts talking about doing literally the opposite of that it’s, of course, going to raise questions, such as:

  • Is that good for you?
  • Is that bad for you?
  • Does that speed up weight loss?
  • Is it the road to eating disorders?

And part of the problem is that generally the only people talking about it are either staunchly for or against IF and so their answer to those questions says more about their personal beliefs than it does about the reality of the situation. Here, I don’t have the space to delve into every fine detail, but I would like to present a primer – a brief overview – that will give you insight into what IF is, how you can set it up, and whether or not it’s a good idea, but before I do there’s something that needs to be covered right away:

Intermittent fasting is NEUTRAL for both health and weight management. I’ll explain what I mean starting with the latter point.

While people will try to state that ‘it’s more complicated than that’, and it sort of is when it boils down to it, your fat storage and loss can be illustrated using a building with a revolving door. People come in and people leave (much like stored fat comes in and leaves) and the net number of people (and the net amount of fat) is dictated simply by the balance between the rate of these two actions.

A regular eating schedule is the equivalent of a steady flow of people entering and leaving at the same time, while intermittent fasting is simply the equivalent of having loads of people leaving during the day followed by a massive influx of people at night.

If you’re eating at calorie balance, that means that maybe 300 people leave and 300 people enter during the day – whether they literally go one-in-one-out, or whether the building empties during the day before 300 people arrive at the last minute or not doesn’t really matter, the nett result is the same.


Body fat works on the same principle – if you are eating at maintenance then you will release a little body fat during the day and also store a little. Whether you keep a steady flow of food coming in with a small amount of body fat oxidation – say you burn 2500kcal per day and eat 2500kcal over 16 waking hours – or you burn a lot of body fat and then store a ton by eating all 2500kcal in one sitting and simply replacing what you released the net outcome is exactly the same. The only way to NOT store the same amount of body fat from that one meal as you have released during the day is to eat less than 2500kcal, thus creating a calorie deficit and so adhering to the same principle as everyone else. The same goes whether you fast for a portion of every day, or for 1-2 full days per week, if you’re eating the same amount of overall calories then the outcome will be exactly the same.

And as for health? Put it this way: EVERY SINGLE proposed benefit of intermittent fasting, be that improved insulin sensitivity, reduced inflammation, increased autophagy (think of this as cell self-cleaning), reduced cancer risk, improved blood glucose and triglycerides, is also improved when people restrict calories and lose weight.

And in studies where intermittent fasting is not combined with a calorie deficit? These benefits are not seen.

In short, whenever anyone talks about the benefits of intermittent fasting, they are talking about the benefits of losing weight. Literally every single time – there is nothing else to it.

So why WOULD you fast? Well, there are some benefits:

  • It’s an incredibly easy way to create a calorie deficit without counting calories. If you don’t eat for most of the time you tend to eat less – who would have thought!?
    • This even holds true if you slightly overeat during eating times. If you skip breakfast you tend to eat more at lunch, but when studied people will cut out more calories by skipping breakfast than they gain through their bigger lunch so it’s a net win. The same goes when people fast for 24 hours then eat for 24 hours and repeat – they eat more when they eat, but not by as much as they have cut out
  • It reduces food fixation and decreases decisional fatigue. When you’re fasting you don’t think about food because you don’t need to, and if you’re considering having a snack all you need to think of, rather than worrying about whether you ‘should’ have it or not, is what time it is. Only when you fast do you realise how much you need to think about food if you eat 4-5 times per day
  • You save time – not eating breakfast makes life easier if you have busy mornings
  • In studies looking at overweight populations fasting DECREASES hunger
  • Your blood sugar will be fine, your body is very clever and will manage this – I’ve said it a million times and will continue to say it: the only people who need to worry about blood sugar are athletes competing for a long time and people with diabetes
  • It teaches you that hunger isn’t actually that bad
  • It can be used occasionally to create a calorie sink – going out for a big meal tomorrow? Either fast until the meal, or if you feel that will cause you to binge then fast today and eat a normal meal tonight, then eat normally tomorrow before not worrying about the meal (this will help because you won’t go to the restaurant/your friend’s place, etc hungry).

But, of course, there are downsides

  • In some people, hunger is increased
  • In some people, food fixation increases because they spend their fasting window thinking about their eating window
  • While in some studies binge eating disorder is improved, it often isn’t and for obvious reasons
  • Breakfast foods are delicious and you don’t get to eat them all that often
  • If you exercise in the morning and fast both before and after that will limit recovery and muscle growth

Many of these downsides, however, can be solved using a simple mantra – IF is a tool, not a lifestyle, and as such, you can choose when you do and do not use it. If you have decided you want to intermittent fast but then wake up really hungry one day, or spend a night in a hotel and the breakfast looks amazing, then just don’t fast that day. It literally doesn’t matter.

If you want to IF but train in the morning, then just train, have a whey or vegan protein shake with water at about 150kcal, then just sort-of-fast until lunch. No, you’re not fasting in the technical sense, but as I’ve already explained that literally doesn’t matter because fasting is ultimately just a way to control calories and so there is absolutely no harm in doing it this way.

So how do you set it up? Well there are a few ways, all of which can be done every single day/week, can be done only on occasion when you’re either not hungry or you’d like to create a calorie sink, can be done on holiday, or can just be done every now and then to increase your calorie deficit while dieting. This list isn’t exhaustive but it’s the most common:

  • 24-hour fasts. Eat dinner tonight, then don’t eat until dinner tomorrow. This is usually done 1-2 times per week on days when you aren’t going to train and are going to be busy
  • 16 hour daily fasts. This is hyped up to be something but let’s be honest this is skipping breakfast – wake up, then don’t eat until about 1 pm. This is really useful for people who exercise because it means you can eat before training in the evening
  • Weekly pseudo-fasting like the 5:2 diet. Eat about 500kcal per day twice per week, then otherwise eat normally

Some people will fast for longer but to be honest anything over 24 hours isn’t really necessary and I don’t recommend it. Because people are stupid when they are on the internet, fasting groups and communities seem to egg each other on to become more and more extreme, leading to fasting for a week at a time etc being promoted – don’t listen to stupid people and, if something sounds like it’s really extreme it probably is. If you want to fast more than 24 hours, first ask yourself why and second please do so under some kind of medical, or at least professional coaching supervision.

But also, just don’t, because there’s no benefit.

As a final set of thoughts, here are some things that apply when looking to implement a fasting approach:

  • Food choices still matter – protein is very important as are vegetables, though if you’re fasting for more than 16 hours per day they can be hard to get in so multivitamin and possibly protein supplementation (depending on needs) may be needed
  • If fasting before training, don’t fast after. If fasting after training, don’t fast before
  • Stay hydrated during your fast. Some religious fasts necessitate abstaining from water but outside of that just don’t
  • Don’t fast for fasting’s sake, and don’t be tempted to do more and more. It’s a method of calorie control and nothing else, and if you don’t feel good, if it doesn’t suit your day, if you’re finding your relationship with food to be suffering, then just don’t do it
  • Calories still count. It doesn’t matter if you fast for 23.5 hours per day and eat all your calories in one sitting: if you nail a big ass pizza and a pint of ice cream in that sitting you can still gain weight
  • Be flexible. Don’t fast when you don’t want to, don’t feel the need to make your ‘eating window’ a rigid and set time, and don’t identify with the method. IF is not a personality trait, it’s a tool, and while it’s useful it’s not magical so you don’t have to be a strict adherent in order to make it ‘work’

So there it is in a nutshell – IF is just planning to not eat for some or all of certain days. It’s a little underwhelming when you actually look at what’s really going on, but if anything that’s a good thing – that means you can use it when it suits you and ignore it when it doesn’t.

Just another tool in the box.

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