The premise behind IF is incredibly easy; you simply don't eat for a prescribed time period in your day/week. Clearly I'm not going to leave it there, that would make a pretty crap article. So I am going to be detailing two popular methods of incorporating IF, both of which have theory behind them and practical results to show. First a little anecdote from one of my fitness buddies which essentially captures IF in a nutshell:
Tales from the Austin streets: While walking to work this morning, I start to pass the bus stop at Congress and Cesar Chavez. A man in his 40s or so grins at me, holds out a huge plate of muffins, and says, "Breakfast, $1!" I laugh and say no thanks and keep walking past him, and he says, "Fruit! I have fruit too!" I shake my head and say, "I don't eat breakfast!" and keep walking. He looks me up and down, slowly, and then [looks] right at my ass and says, "It's working. Whatever you are doing, it's working!"
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| I have no idea if she practices IF, but it's also working |
So on to the practicalities of IF. Firstly 16/8 (or Leangains) style; 16/8 refers to an 8 hour eating period and 16 hour fast period per day. Obviously you are fasting throughout your sleep (unless you have some impressive sleep walking habits) so the 16 hour fast is not as hard as it might initially sound. The important factors are that you eat all your calories inside the 8 hour window, which should be at more or less constant times, and that you eat as many calories per day as you would otherwise. It is only the timing of your nutrition you are manipulating here, not the nutrition itself. During the fast you can and should drink lots of water and can also drink black coffee and teas if you so wish. An example of a day on this sort of plan may be a morning black coffee, breaking your fast with lunch at 1 pm, having a small snack pre-workout at around 5 pm, then having a large post workout meal at 8.30 pm.
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| Not quite this large, but still pretty large. |
This is the type of IF that has received a large amount of mainstream attention, with the 5/2 diet hogging the limelight. There is nothing wrong with this style for the sedentary masses; however for someone putting a substantial amount of effort into training, 2 days fasting a week may be a bit much. Furthermore, the commonly publicised versions of the 5/2 diet allow you to eat a low number of calories on your ‘fasting’ days; firstly, this isn't fasting and secondly, it reduces many of the benefits of fasting and will likely cause you to be much more hungry than you would be on a full fast. So a full fast for a single day a week is usually the preferred choice for active individuals.
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| Charles Bronson is reported to fast every Sunday. I'm unsure if this is beneficial to my argument. |
Before we get into all the good aspects of fasting, I should probably play mythbuster and squash some of the fallacies which many have been led to believe by archaic advice in mainstream media, gym bros and supplement pushing muscle mags.
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| "Eat 12 meals a day to look like me, I recommend 6 of these meals are 4 scoops of SuperMuscle's OverpricedProteinOatsAndShit7200" |
A popular fact that is regularly brought up in discussions is that those who eat breakfast tend to have lower BMIs than breakfast skippers, this is entirely true and has been shown in multiple studies. However, there is a saying in science 'correlation does not imply causation'; just because two things show a statistical link, it does not necessarily mean that one causes the other. The majority of these breakfast studies are simply done by measuring people's BMIs and asking them to fill out a questionnaire on eating habits. The average breakfast skipper is far more likely to be someone with disorganised eating habits (which are conducive to weight gain) and have a higher disregard for their health (which is exactly what this study showed); they are not someone consciously deciding to skip breakfast as a method of manipulating their nutrition. Now there is nothing wrong with breakfast, it is simply not a magic weight control solution like many claim.
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| Something this delicious is not going to be the answer the obesity epidemic. |
More astute minds might point to the fact that insulin sensitivity is high in the morning, thus it is a beneficial time to eat from a muscle building standpoint. This again is true, however, insulin sensitivity is not high due to the time of day, it is high due to the fact that you have just been fasting through your sleep. Prolonging this fast will only cause a greater increase in insulin sensitivity for the first meal.
Perhaps you are worried that you will feel hungry throughout the fast. Thankfully, evolution has your back, there is a hormone called ghrelin which regulates your appetite by rising when food is 'expected' and falling after eating. The good news is that ghrelin can effectively be 're-trained' to be secreted at different times, thus after a few days of implementing short fasts, you won't feel hungry during the fast, as your ghrelin levels will not be rising in expectation of calorie intake (I'm writing this at 1.10 pm, everyone around me is eating, I haven't had a bite all day and am not hungry at all).
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| "Guys, I'm hungry, I haven't eaten since last night." Said no real man ever. |
"Starvation mode!" the masses cry. Yep, it's true our body does indeed have a starvation mode, our basal metabolic rate will indeed drop as an evolutionary survival mechanism if we are starving. However, starving means starving; none of this "I'm starving, I haven't eaten in 5 hours" balls, I'm talking 'haven't eaten in 60 hours' to start to see any metabolic downturn from 'starvation mode'. As the longest I am suggesting you fast for is around 32 hours and my preferred method of IF prescribes 16 hour fasts, you are safe from any sort of starvation.
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| Think more sexy Bale, less skinny Bale |
What about eating frequently to 'stoke the metabolic fire'? Gotta eat every 3 hours right, bro? In short, this is bollocks. You see, your body is a little bit more sophisticated then a wood stove, so the 'logs on a fire' analogy is borderline retarded. The standard wisdom peddled is that 6 meals a day will cause you to build more muscle, lose more fat and get generally jacked and tanned. However science did its thing and found "no evidence of improved weight loss" with more frequent meals and actually found that people were more sated with 3 meals versus 6 (with total calories equal). The myth originates from the fact that eating raises your metabolism, this is known as the thermic effect of food or TEF. Someone once upon a time simply took this fact and ran with it, hypothesising that if eating raises metabolism, then eating more frequently raises it more. The fact however, is that TEF is dose dependent; three 400 calorie meals and one 1200 calorie meal (with identical macronutrients) will cause the same number of calories to be burned through TEF. Ever got the meat sweats at an all-you-can eat? That heat is due to a hefty dose of TEF from all the calories you are taking in.
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| Joey, TEF. TEF, Joey. |
So big meals are good from a satiety perspective and all the same in terms of raising your metabolism; what about protein synthesis? Some of you many have heard that you can only absorb 30 grams (or some similar value) of protein per per meal. This is again a case of someone taking a fact and making wild hypotheses that have since been taken as fact by the masses. It was found in a study that protein synthesis was maxed out with a 30 gram dose, and that higher does did not achieve any greater synthesis. People ran with this and claimed that anything over 30 grams of protein in a single sitting was useless. Not true. What the aforementioned study found was simply the minimum dose for maximum protein synthesis, if you eat more protein, the protein takes longer to digest and the maximum rate of synthesis continues for a longer time, your body still uses all the the protein. Food takes a pretty long time to digest and be assimilated, this study shows that a standard meal of 75 g starchy carbohydrates, 37 g protein and 17 g fat is still being digested and absorbed after 5 hours (and that is pizza, a crappy, refined food which is absorbed relatively quickly). There is even some evidence that eating the majority of a day's protein intake in one meal improving protein retention (granted this is in elderly women). Otherwise in young, healthy women, there was no difference in protein retention whether it was eaten spread over the day or in one big meal.
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| Eat all the protein. |
Eating big meals at night (especially dreaded carbs) makes you fat, doesn't it? As I'm crushing everything you think you know, you might be able to predict the answer to this one. Observational studies have found that late night eaters are fatter than those who tend to eat earlier, however, this is again a case of lifestyle choices and dysfunctional eating habits. Those that eat a large amount of calories later in the day tend to be sedentary people snacking, they also tend to take in more calories overall and have less sleep, which leads to being fat. The habits of the average, lazy couch potatoes are of no consequence to you fine, heavy-lifting, health conscious readers. On to studies that matter then; when participants were given identical meals, but fed at different times of day, eating the majority of your calories later in the day was shown to be better for preserving lean mass and losing fat, time and time again. As an added benefit, eating a large amount of calories, especially those from carbohydrates, late in the day, will active your parasympathetic nervous system, allowing you relax and sleep with greater ease.
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| Big protein and carb meals in the pm = big gains |
In the above myth debunking I have mentioned or alluded to multiple reasons why IF is beneficial, but lets do a full run down. Fasting improves your body's peripheral insulin sensitivity (that is, the insulin sensitivity of fat and muscle cells) and reduces serum glucose levels, both of these serve to improve body composition. Fasting reduces oxidative stress and has been shown to be neuro- and cardio-protective. In practice this means that IF can essentially make your body more resistant to the declines that come with age, pretty cool stuff. Fasting increases catecholamine production, you've heard me mention these things before, they are better known as adrenaline and noradrenaline. If their production is upregulated, fat burning is upregulated and you feel more alert. Feeling more alert is going to be a positive thing in the early part of the day when you want to get things done, your cognition will not suffer as a result of fasting (even fairly long term) either, so you will be more focused and just as able to think clearly as when fed.
The above benefits are all pretty nice; you feel alert, your body is protecting itself from oxidation and increasing insulin sensitivity, priming you for better muscle gain. However, the reason most people look to IF is fat loss, fortunately, this also stacks up pretty well. Fat oxidation was shown to be increased during day long fasts, growth hormone has been shown to increase (which contributes to fat burning) and fasted training has been shown to give greater fat loss in healthy male subjects. In a study where healthy adults were fed all their calories in only one meal a day, there were modest decreases in fat mass and increases in lean mass with absolutely no reduction of calories. In a recent study on rats (which are actually pretty transferable to humans generally) some rats were fed all day, where others were fed all their calories during an 8 hour window (sound familiar?), both groups were fed a high fat diet. The group that were fed all day got fat, developed diabetes and liver diseases; the time restricted feeding group developed none of these things. Now this is limited by the fact that it is a rat study, but still, there are some pretty cool findings.
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| It's not his fault, it's his feeding schedule |
So hopefully you can see, IF is a pretty promising diet strategy. A recent review sums it up nicely:
Animal models have shown positive changes in glucose (lower plasma glucose and insulin levels) and in lipid metabolism (reduced visceral fat tissue and increased plasma adiponectin level), and an increased resistance to stress. Despite the limited number of samples studied, positive results have been reported on the impact of IF for human health. IF is reported to improve the lipid profile; to decrease inflammatory responses, reflected by changes in serum adipokine levels; and to change the expression of genes related to inflammatory response and other factors. Studies on obese individuals have shown that patient compliance was greater for IF than other traditional nutritional approaches (calorie restriction), and IF was found to be associated with low oxidative stress. Recent reports suggest that IF exerts a positive impact on the metabolic derangements commonly associated with cardiovascular diseases, and that it may be a viable and accessible intervention for most individuals.
Clearly I like IF, and personally I prefer the 16/8 version. This is mainly due to the daily cycle nature of it, I prefer eating the same way every day and this also has more beneficial effects on ghrelin levels which will regulate your appetite, causing you to be less hungry during the fasting period. 16/8 style also has the benefit of a daily increase in insulin sensitivity, causing a greater anabolic response when you break the fast. 6/1 style still brings great benefits, it will still cause an increase in insulin sensitivity, an increased rate of fat oxidation on your fasting day and bring about all the beneficial neuro and cardio-protective effects, possibly to a greater degree than 16/8 fasting due to the longer fast. However, some may experience greater hunger when implementing 6/1 style due the the lack of adaptation of ghrelin (as it is 'reprogrammed' on a daily, not weekly, cycle). Overall, both styles are beneficial, but not a complete diet panacea, this is not some grand secret to eating whatever you like and looking great, but it is a useful tool for improving body composition which appears to bring some beneficial health benefits as a welcome addition.
Update: Fasted training - I didn't put this in originally as the article was running on, but I was asked the question, so here are my views for anyone interested.
Light cardio when fasted is fine, however if you want to perform heavy weight training or HIIT in the fasting period I would recommend (a la Berkhan) semi-fasted training; consuming ~10g BCAA (preferred) or ~20g whey. This is simply to get some aminos in your bloodstream as a safeguard from any catabolism due to de novo gluconeogenesis from the high intensity of training, whilst keeping the majority of the beneficial effects of fasted training (greater fat oxidation, increased anabolism from post-workout feeding due to increased insulin sensitivity).
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