As with many diet fads, intermittent fasting (IF) comes and goes. It picks up steam within certain communities and then gradually falls off as another fad comes along and presents itself as the better alternative.
I’ve seen a lot of information about intermittent fasting around the internet lately, so I figured I’d take a second to debunk some popular myths regarding this dietary strategy.
“Special” Fat Burning
First is the idea that fasting promotes some sort of special “fat burning process.” The prevailing idea is that after 10-12 hours of fasting, your body enters ketosis and your brain starts using fatty acids (instead of glucose, it’s preferred energy source) for fuel.
However, isn’t it a little unbelievable that after only 10 hours your brain has depleted your entire body of it’s stored glucose? The liver alone can store somewhere in the realm of 100 grams of glucose at a time, roughly the same amount of glucose that your brain needs for an entire day of looking at memes on Instagram and refreshing your email inbox. That would mean you’d only be about halfway empty by the time you reached lunch.
Ketosis isn’t like changing your clothes. In fact, it can take multiple days to deplete glycogen stores and ketosis often comes with sluggishness & headaches as your brain makes the switch. This would be made worse by a constant “in” and “out” of ketosis. But don’t worry, your IF diet likely won’t get you there.
The common argument here is that the quick, 12-hour switch to fatty acids as your fuel source is an evolutionary trait – we’re designed with this back-up system. But if we’re going to use the evolution argument, wouldn’t it also make sense that your body would store glycogen (it’s preferred fuel source) for more than just a normal eight-hour workday at the office?
The truth is that your body burns through both carbohydrates and fats differently throughout the day based on the intensity and duration of your minute-to-minute activity level. It can take multiple days to enter ketosis, not just 12 hours.
Extra Weight Loss
Another common misconception with intermittent fasting is that these diets somehow drive immediate and sustainable weight loss. Fasting is supposed to increase growth hormone production, thus increasing the rate of fat burning.
And in the case of weight loss, some of this myth is partially correct. In the absence of food intake, glycogen depletion will be accompanied by dehydration. In fact, the human body retains approximately three parts water for every molecule of glycogen that it stores. As glucose is used up and not replenished, this dehydration creates weight loss. However, this weight loss is not true fat loss and the weight lost will be reacquired when food and fluid intake begins again.
True fat loss can only be achieved through a negative energy balance over time combined with adequate protein intake and anaerobic exercise.
Periods of fasting impede your body’s ability to synthesize new proteins. As protein breakdown occurs naturally and amino acid turnover occurs, the lack of incoming amino acids make a loss of amino acids inevitable.
This deficit would probably be neutralized at best during the feeding period, making lean mass retention actually more difficult (note that I said more difficult, not impossible by any means) during IF. Of course, this would depend largely on the ratio of fasting to feeding.
In the end, you’ll probably want a steady stream of amino acids to replenish the body’s amino acid pool and some anaerobic exercise (a.k.a. lifting & sprinting) to create the right hormonal environment. These extra pieces ensure that you’re losing fat, not just weight.
A Hidden Secret
A third myth perpetuated by the intermittent fasting community is that the food industry somehow has a stake in not telling you the truth about intermittent fasting and it’s benefits.
While I can agree that the food industry probably isn’t the best place to look for an unbiased look at health and wellness, it’s not safe to assume that they are withholding some ultra-important nutrition secret either.
The idea is that a diet based on intermittent fasting is also one of “less eating,” which would mean less business for restaurants and food stores. While this might be true in some cases, IF does not guarantee a smaller caloric intake and, although it might hurt breakfast venues, it might actually work in favor for the dinner industry as hungry fasters make irrational decisions in their evening search for sustenance.
IF & Exercise
And what about morning workouts? While many in the IF community rave about the increased brain function (which I’ll touch on in just a second), those that are fasting through their workout and for many hours afterward are missing out on key times that the body might be more sensitive to proteins and carbohydrates.
This means that you’d be leaving valuable #gainz on the table by not consuming food around your workout.
And what about nighttime workouts? If you’re worrying about stuffing your face with an entire day’s worth of calories like you’re in an 8 hour eating contest, can you really afford to lose a couple of hours to exercising?
Intermittent fasting, practically speaking, works really well for some schedule-wise. However, if it doesn’t fit your schedule, you can’t workout on an empty stomach, or you’re a nighttime exerciser with a short fasting window, I wouldn’t count on IF working out long-term.
The Pros of IF
So maybe intermittent fasting isn’t the best choice when it comes to overall performance or body composition, but how about that extra alertness throughout the day?
As somebody that has tried intermittent fasting at length in the past, I can vouch for the increase in awareness that seems to come with an eight to 12 hour fast. When the brain is put under the mild stress of not having fuel, it seems to improve it’s own efficiency through the development of neurons and synapses. In simplest terms, your brain builds more efficient wiring through which to communicate within itself and with the rest of your body.
From a psychological perspective, I enjoyed what fasting taught me about hunger and thirst cues. These feelings (at least for me) often come in waves – they calm down after a while and then start back up again. This doesn’t mean you should ignore these cues, especially thirst, but it was an interesting discovery.
On the other hand, intermittent fasting hampered my ability to get through my workouts. Despite eating adequate calories, I found myself with headaches throughout my workouts and for the days afterward. Of course, this is probably dependent on the type of workouts being performed and will vary greatly from individual to individual.
Additionally, strong hunger cues and general life stress can lead to an overload of the hormone ghrelin and (more importantly) turn you into a kitchen gremlin wherein anything and everything is on the table (literally). See here.
On the surface, intermittent fasting (and other related nutritional philosophies like the 5/2 diet) can be an attractive diet option for many busy people. But as is the case with most health & fitness question, the right answer can depend.
It depends on your goals. If you’re looking to give your digestive system a break, feel more alert in the morning, or just lessen the stress of eating throughout your morning and work day, maybe IF is for you.
If your goals involve performance, body composition, or overall health, it might be worth it to look a little deeper before you make the commitment.
Don’t be fooled. Intermittent fasting doesn’t have any special capacity for fat loss. The rules still apply; create a negative energy balance, eat your protein at regular intervals, and lift weights.
But just to end this article on a lighter note, remember that you’re technically fasting already. It’s an eight hour fast … while you’re sleeping.