Intermittent Fasting (IF) is very simple: eat sometimes, don’t eat at others. While most humans do this by default when they sleep every night, IF advocates extend this period for a number of reasons.
There are various kinds of IF. Take Eat Stop Eat, by Brad Pilon, for example, which advises one or two 24-hour fasts per week. He advises you eat dinner one day and then fast until dinner the next day, thus leaving a 24-hour gap but not actually spending any one day not eating. This is the simplest form of IF, and can be highly effective for those who spend a lot of time travelling or who are very busy. However, it can have serious repercussions for athletes.
LeanGains by Martin Berkhan, meanwhile, involves a 16-hour fast followed by an eight-hour feeding window (or 14/10 in women, the reasoning for this being that there is a small amount of evidence that extended fasting can cause adverse effects for the female hormonal system). This is probably the most popular version of IF, which has a number of different approaches within it – all of which can be checked out on the LeanGains website.
The Warrior Diet by Ori Hoflmekler advocates a 20-hour fast followed by a four-hour eating window. The theory behind this is that humans are ‘nocturnal eaters’ and that this fits in with our circadian rhythm. While this isn’t true, it can be seen as a more extreme version of LeanGains possibly useful for those who are elderly or otherwise highly inactive for most of the day, and who do not train intensely.
Similar to Eat Stop Eat is the recently popularised 5:2 diet which involves, again, one-two fasting days per week, but rather than fasting for 24 hours dinner to dinner, you eat normally one day, go to sleep and then the following day consume 400 or 600 calories (depending on sex) throughout the whole day. This, much like Eat Stop Eat, can be good for those who are busy, but because of the extreme morning-night restriction it’s closer to the Warrior Diet for being useful for those who aren’t all that active. While this isn’t strictly IF, it’s usually referred to as such.
Proponents of intermittent fasting claim it is a tool that can be used to speed up fat loss, or get someone training for fat loss past a plateau, without changing their food intake. This seems plausible, as fasting has one distinct action to increase fat loss; it increases the secretion of ‘stress hormones’ cortisol and adrenaline.
These two hormones play a number of different roles but in this specific context they upregulate lipolysis – meaning they help fat cells release fatty acids into the bloodstream for use as fuel. More fatty acids released and used, faster fat loss – right?
Not quite – because the fasting window is followed by a feeding window.
An IF proponent will eat far less food during their fasting period, but then they will eat more than usual to fit their normal intake in a smaller time frame. This causes more rapid fat gain in this period to counterbalance the aforementioned fat loss resulting in a net zero.
Summed up, your fat cells store and burn fat all of the time simultaneously and it’s the balance between these two processes over an extended period of time that dictates changes in body composition. This state of storage and burning is similar to a rotating door on a bar. It lets people in and out all of the time, sometimes more come than leave and sometimes more leave than arrive, and the amount of people left in the building at closing is dictated by the balance between the two – not the sudden rushes or the extended quiet periods.
Intermittent fasting can have profound effects on a person’s ability to adhere to a diet. The two main things which result in people failing in their fat loss goals are hunger and cravings, and IF can help solve both of those.
Hunger is largely habitual, meaning you get hungry at the times you usually eat each day rather than when you specifically need food. Your body likes routine and cycles, and this is one example of many – the hormone grehlin is what ‘tells’ you that you’re hungry, and it can be manipulated intentionally by altering your eating pattern.
If you always eat at 8 and 11am, you will always be hungry at 8 and 11am because grehlin will be released then in order to make sure you eat, and this can make fat loss a bit of a pain. If you decide to start skipping these two meals then after a period of around two weeks you will find that the hunger you used to experience is no longer there.
Cravings happen during a dieting phase (when not due to genuine hunger) because some nice foods that you enjoy can be difficult to ‘fit in’ to a reduced total intake. Think about it – if you have 1,800 calories to play with and eat four meals per day, then that is two 500 calorie and two 400 calorie meals – which are hardly going to touch the sides.
If you decide to drop this number to two meals, you can suddenly eat two 900-calorie feasts, which will be highly satiating, and which will allow you a little more freedom with food choices. Feasting every day on foods you like, while not being hungry, can make dieting feel like a weight gain phase for some people – and that’s a good place to be.
Secondary to this, a lot of people find the clear “Eat now”, “Don’t eat now” rules of IF make cravings disappear as they simply forget about food at all. If you’re focusing on other things, staying busy and not hungry, it’s much easier to avoid high-calorie things that will easily eradicate a calorie deficit.
Because of the above, Intermittent fasting can be considered a powerful tool in fat loss, even if it doesn’t really help you lose fat directly.
For completeness, though, I need to mention the downsides to this aspect of IF. After going a full day (or even a full morning) without eating, some people will find hedonistic tendencies are amplified. Overeating after a period of complete food abstinence is very common and must be considered. If you or a client don’t deal well with hunger and tend to find it makes you overeat (or want to) then IF might not be the best idea for you.
IF might not directly help or hinder fat loss (though it can improve it indirectly) but can it make you a better athlete? Some people think so.
Fasted training should, by way of logic, impair performance. You’re training on an empty stomach so you have no ‘fuel in the tank’, and surely your blood sugar ends up crashing, right?
On the flipside, fasted training is purported to be great for performance as it effectively upregulates the ‘fight or flight’ response as mentioned earlier. This sudden release of adrenaline brings with it a stimulant-like energy, which can feel euphoric – this can indeed improve focus, concentration and creativity – but this is not the same as increasing physical performance.
There is actually a pretty substantial amount of evidence in this area thanks to those practicing Ramadan. What we notice is that there is no impact on training…at all. What we can take from this is that, at least from a resistance training perspective, overnight fasting (and even longer) probably won’t kill gym performance. Of course endurance training will be affected, but because resistance training doesn’t typically deplete that much glycogen anyway, you can rest assured that so long as you eat well during the eating window, fasted training will not impair performance (at least it won’t as soon as you get used to hunger pangs).
There are some who say that fasted training will inevitably lead to your muscles wasting away, and there are those who state that it will increase the anabolic effect of your next meal thus actually increasing muscle growth. They are both correct, and yet they are both mistaken. Roughly, muscle protein synthesis (growth) and muscle protein breakdown work in the same manner. So, if you train in a fasted state you will indeed cause muscle degradation to accelerate, but then the post workout meal will create an amplified anabolic effect. This process and the fat gain/loss processes are perfect examples of ways that, simply, your body is smarter than you.
The only real exception to this rule may be fasting before and after training. There is a small amount of evidence that after around two-three hours of fasting after a fasted training session, stress hormones such as cortisol have been raised so high that muscle loss exceeds what the subsequent meal can counteract. Because of this, you should eat as soon as is convenient after a fasted training session.
Depending on your protocol of choice, eating enough food to gain weight and therefore muscle is going to be hard. Sure, in a beginner it is possible to gain some muscle at maintenance caloric intake, but sooner or later you’re going to need a surplus, and that means that you’re going to have to eat.
If you are restricting food intake to four or even in some cases eight hours, you are going to struggle to maintain optimal caloric intake whilst also eating the kinds of foods which will promote optimal health. Anecdotally people find it hard to consume enough fibre and wholefood protein in this time without being bloated and uncomfortable – especially with one-two meal approaches.
There is a growing amount of data that suggests distribution of protein matters. Not as much as total intake of course, so it’s not make or break, but there appears to be a clear difference between three-five ‘pulses’ of protein per day and 1-2 bonus doses. This is because, in simple terms, you can only stimulate so much muscle growth with a meal, and it’s only stimulated for a short time regardless of how much you eat. That means that once muscle growth is maximally stimulated, eating a bigger meal doesn’t do any more for you in terms of muscle growth signalling.
If you eat in a four-hour window, you’re only stimulating muscle growth for that time and maybe three hours afterwards, but if you spread the same intake out over a 16-hour waking period you’re getting far more growth stimuli. This may add up over time (though it’s not conclusive yet).
If the above questions throw up no red flags, consider one of the approaches mentioned safe in the knowledge that aside from potentially making your schedule easier, or your diet more convenient and easy to adhere to – IF isn’t magic and not much will happen.