What Is Intermittent Fasting?
Over the last few years intermittent fasting (IF) has really started to gain ground amongst those who have been looking to shed excess body fat. Which is not surprising really! Especially when you consider that when it comes to losing body fat, it’s no easy task. In fact, it’s not a pleasant experience at all. The lingering hunger, feeling like a zombie, the constant mood changes, the cut backs in foods (especially the ones you love!), being more fussy in general about your nutrition choices and generally, having less energy to get on with your day-to-day activities
Well then, I guess you can imagine that if something pops up that is supposed to help aid your weight loss efforts, most people are going to jump on it it like fresh hot cakes coming out the oven. I think anyone would, no surprise there! Like most things in life, there will always be people who are dedicated followers of something. IF is no different. There are some people who say it’s superior to your typical sustained calorie restriction diet, and have had great weight loss success with it. Great! But, there are also those who simply see it as another over marketed method of simply trying to balance your calories in favour of weight loss. There is nothing magical about it, it doesn’t change the basic principles of calories in/out (which is how weight loss occurs).
Which crowd is really on the right lines?
⇒Does IF really provide a superior method to loosing weight in comparison to the standard way of simply reducing calories in a sustained manner over time (continued energy restriction)?
⇒Does IF actually do something differently that makes fat loss easier, more effective and faster? What does the research say?
⇒OR, is IF simply a method people choose to use as a matter of convenience? Does this increased convenience lead to better adherence during their weight loss efforts? In other words, IF might be more effective to some simply through providing increased convenience, not because IF acts through some specific mechanism of action at the physiological level.
So how is IF actually structured? Well, IF is not one standard way of fasting, how you do it is up to you. If you look into the scientific literature on IF, they all use the terms IF, but how they set up the IF protocols might slightly differ (which might make it slightly confusing, but don’t worry it’s not that bad!). But in general, IF usually consists of periods of normal eating followed by short periods of severe calorie restriction (and could range from 1-7 days, consecutive or non-consecutive). With calorie restriction on fasting days ranging between 0-50% of your daily energy (calorie) requirements.
⇒NOTE: In the scientific literature the IF protocols are compared against something known as continued energy restriction (CER). Essentially, this is what most of us do when we want to lose weight. We stick to a determined calorie deficit each day, rather than alternating between normal (eating at maintenance) and fasting days, as in IF.
A few IF protocols you might come across in the literature:
⇒The 5:2 Regime: This is basically eating normally for 5 days, with 2 consecutive or non-consecutive fast days (in which calories are significantly reduced)
⇒The Alternate Day Energy Restriction Regime: This is essentially ‘fasting’ every other day, in which the fasting days usually consist of restricting your calorie intake by 60-70% of your daily energy expenditure.
⇒The Eat:Stop:Eat Regime (brutal!): This is really eating normally one day, then a ‘total fast’ for 24 hours the next (no consumption of calories on these fasting days).
⇒The 16:8 Method: This involves restricting your ‘eating window’ to 8 hours and then ‘fasting’ the following 16 hours.
What Does The Science Tell You About IF And Fat Loss?
Given the popularity of IF for weight loss, there have been quite a few studies conducted over the last few years to see if IF is as good as people make it out to be. If I can say now, after having looked over the research that has been done, It doesn’t seem to measure up to it’s popularity among the general public! In fact, when it came to investigating the effects of IF on reducing bodyweight and body fat in obese and overweight participants (of equivalent energy intake, that is important!), researchers found that IF was equally effective as CER at reducing bodyweight and body fat in these individuals (You can check out a few of the studies published here: Seimon et al, 2016; Harvie et al 2010; Ash et al, 2003).
*NOTE: It’s important here to realise that all these studies are done in overweight or obese participants. Which leads to the question: What would be the effect if these studies were to be replicated in normal weight participants? For instance, fitness enthusiasts or those who want to get even leaner than just normal (say for a bodybuilding contest). Would IF have any increased effect over CER in this case and thus prove a more viable method? Would the results be completely different to those obtained from obese and overweight participants? Who knows! It’s interesting to further look into.
⇒What can we conclude? At the moment, the research seems to be pretty clear cut (at least in those obese and overweight), that IF has no added effect over CER in terms of promoting bodyweight and fat loss. When calorie intake is the same over the course of observation, both IF and CER cause fat loss and the extent of this fat loss is comparable between the two dietary methods. This tells you for certain one thing, that your trusty old friend calories in/out still rules the day in terms of fat loss promotion.
The bottom line: At this point in time, you cannot say IF is better than traditional CER in the context of producing pure fat loss. It produces fat loss, yes! But, it seems to work through the same mechanism as CER for promoting fat loss: that is simply shifting the energy balance in favour of fat loss (calories out is greater than calories in).
Why Might People Use Intermittent Fasting?
So the science says that IF is no better to traditional CER for producing weight loss. Then why use IF? Why torture yourself through periods of fasting? (Well, for me it would certainly be torture!). Interestingly a study was brought out in 2016 by Seimon et al, that looked at the differences in weight loss efficiency in obese-induced mice (yes ok, mice not humans, but it still gives some interesting insights!) that underwent either IF or CER. Here, mice that did the CER protocol, underwent a daily calorie restriction of 82% of that followed by the obese mice fed a ab libitum (unrestrained) high-fat and sugar diet for 22 weeks (control). The mice that underwent the IF protocol, underwent 5-6 consecutive days with a calorie restriction of 82% of the control, followed by 1-3 days of ab libitum intake. Essentially, the total calorie intake during this study was actually greater in the mice that underwent the IF protocol. Which is why it makes this study pretty interesting!
⇒To investigate weight loss efficiency between obese-induced mice following a IF or CER diet. Weight loss efficiency is simply weight loss per unit of energy restriction (metabolic efficiency).
⇒At the end of the study, both the obese-induced mice following the CER and IF protocols lost bodyweight and body fat, and the extent of these total body weight reductions between the two were similar. However, it was found that the obese-induced mice that underwent the IF diet, exhibited significant higher metabolic efficiency in comparison to those following CER, even though their overall calorie intake was higher.
⇒What does this suggest? 1) A higher calorie intake, 2) following IF, and 3) yet a higher weight loss efficiency, what is all this saying? Well, during periods of restricted calorie intake, a huge range of metabolic adaptations might occur in the body in response (pretty complex, won’t bombard you here!). Which kind of makes sense, survival and all that sort of stuff! Your body is found in a state of emergency and needs to conserve as much energy as possible to survive.
⇒It was suggested that periods of ab libitum normal food intake (here termed metabolic ‘rest’ periods) might serve to attenuate the metabolic effects that occur during periods of reduced calorie intake. All while these IF obese-induced mice had a larger overall calorie intake over the course of the study! These metabolic ‘rest’ periods might actually serve to keep your metabolic efficiency high even during periods of calorie restriction, thus accounting for the increase in weight loss efficiency. Although the exact mechanisms for this, were not known from this study (A further study on metabolic ‘flexibility’ to also talks about this in the context of IF can be read here Harvie en Howel, 2017).
My ideas from the study?: Although you attain no additional benefit in terms of pure fat loss between CER and IF, it does seem to bring out a potential positive for IF that I can see being attractive to many people 1) Adherence. Fat loss is not a short-term thing, it takes time. But honestly, no one likes to be in a calorie restricted state for long-periods. It’s depressing, it’s hard and, it is taxing both mentally and physically! This can effect someones willingness to carry on with their fat loss journey over the long-term. Having these ‘reset’ periods of ab libitum food intake might just make everything ‘that tad bit easier’. In a CER diet, you wouldn’t have these ‘diet breaks’. However, I question whether ‘unrestrained’ intake on non-fasted days is actually a wise idea as said in the article.
Although in the article the mice on IF ate more than those on CER, you still have to remember, they were mice and they were obese. The situation was not replicated in humans or those of normal weight. I don’t want people getting the idea that they can suddenly splurge out on massive amounts of calories just because they follow IF! In reality, if you are maintaining a calorie deficit, depending on how severe, regular breaks throughout the diet period (say back up to your maintenance level or just above with clean food, not junk!) might just keep you on the right track. IF might be a good tool to provide this flexibility. On a CER diet, a sustained reduction in calories might not allow for this ‘metabolic rest’ and so everything might slow down as you restrict for longer. Although you will still loose weight (like IF), you might come across more plateaus and slow downs during the process with CER.
⇒I guess what we are saying here is, if IF can keep your metabolism running efficiency, it might make the whole fat loss process for you smoother. Although the extent of fat loss is no different from that which you would achieve from CER, a smoother process during IF, is likely to keep you focused and motivated for longer.
The only problem some people might come across with these whole ‘metabolic reset’ days during IF is getting back on track. Fat loss is all about exercising alot more restraint than what you are used to. If you were to include these ab libitum normal days back into your diet and regularly, it might make it harder to get back into your fasted days. Something I like to call calorie contrast. In other words, some people find it extremely difficult to get back on track if they have days in which they throw their calories higher than usual in order to ‘jump start’ their metabolism. Some find it hard to go from a high/very high calorie day back down to a restricted calorie day. Some people are reminded what it feels like to have a higher amount of calories! If not managed properly, can lead to a downward spiral of uncontrolled binges and urges, especially if your diet is not composed mostly out clean foods. This might makes it difficult to stay on track. Something to consider!
Final Thoughts On IF
The thought of having days in which your calorie intake is severely limited (or even zero) doesn’t bode too well for a lot of people. This can lead to a lot of negative changes such as mood, increased anger, hunger, and failure to carry on with the fat loss plan. Some people need to have food on a regular basis (provided it fits into your total calorie target), me included! Therefore having ‘fasted’ periods might not be the most viable tactic if weight loss is your goal and you want to stick with it for any length of time.
However, others might find appeal in IF for a few reasons:
⇒ Eating in specific time periods, might allow for more of your calories to be had within a relatively short space of time. Giving the feeling that you are eating more and a feeling of fullness (depending on how many calories you have to work with in the first place).
⇒Works well with your daily schedule.
⇒Potentially bigger meals (but again, depends on your ‘feeding’ window and the number of calories you have to work with).
Ultimately, IF might work well for some people through increased adherence. At present, the research suggests that IF doesn’t hold any additional effect of fat loss over CER and thus it’s true effect likely comes from being more convenient for some people than CER. If IF (over CER) makes some people adhere more to their fat loss plan, then fat loss will be achieved. Simply because they don’t quit half way through!
From the research, the strong point of IF over CER might be the fact that it might allow those on a fat loss program to ‘step frequently away’ from dieting. In other words, flexibility. With CER you are constantly in a calorie restricted state. For anyone this is going to be difficult, but for new people engaging on a weight loss journey, this might be impossible. If IF provides the possibility to work in these ‘rest days’ (days of eating normally or at maintenance) and still loose fat in the long-term, then it might be a nice tool to use. If it makes you adhere to your fat loss program, then it’s worth it’s weight in gold! Whether that be IF or CER.
⇒Final thoughts? Ultimately the extent of fat loss with both IR and CER is similar provided you are in a calorie deficit. However, IF might be handy for those in terms of providing increased adherence and compliance in comparison to CER.
Any questions, ask away!