Intermittent fasting is a fairly popular dieting approach that, in the face of broscience and logic, actually works fairly well for helping people lose weight and even retain muscle while doing it.
With tons of different approaches, all with a backbone of fasting, I'm going to briefly dive into what intermittent fasting is, how you can use it to your advantage, and answer some popular fasting related questions.
What is Intermittent Fasting?
Quite simply, this approach of eating includes at least an extended period of what is considered "fasting" or abstinence of consuming foods with a caloric value. Additionally, some people even consider fasting to also include abstinence of substances that need to be metabolized by the liver, such as caffeine.
However, for the purpose of intermittent fasting for us, we'll consider fasting to just include abstinence of calorie containing products.
From here, there are multiple different approaches to fasting. Here are some of the most popular styles and their fasting periods:
Theoretically speaking, when you get acclimated to a period of fasting, there's no stimulus for your cells to secrete ghrelin. Since there's no stimulus, there's no ghrelin and you don't get hungry.
Why is Intermittent Fasting Effective?
Intermittent fasting may be effective for a number of different reasons. Here are the most likely.
1. A decrease in calories.
The primary way that intermittent fasting probably works is a reduction in calorie intake. Think for a moment how we normally eat: wake up, eat, have a snack, eat lunch, have a snack, eat dinner, have a snack, repeat. Throughout the course of the day, you might eat 5-6 meals and snacks.
By restricting the time that you have available to consume food, it's much more difficult to make up for the calories you've missed. Think for a second how long a typical meal lasts in terms of satisfying your appetite. A large meal filled with protein might help stave off hunger for 3-4 hours. Typically, you'd have anywhere from 8-10 more hours to consume food. Now with fasting, you only have 3-4 more hours left to consume food.
As a result, it actually becomes difficult for you to consume the amount of calories you normally do. This results in weight loss.
2. A decrease in hunger
Paradoxically, practitioners of Intermittent Fasting (myself included) often find that fasting actually reduces hunger. This is possible via two mechanisms.
The first is an increase in hormones known as catecholamines such as norepinephrine and epinephrine. These hormones act on a number of different receptors in the body to increase output of your sympathetic nervous system. When increased, the sympathetic nervous system can result in feelings of wakefulness and even hunger.
The second is because of inhibition of the hunger hormone known as ghrelin. Interestingly enough, ghrelin is secreted by cells in the stomach known as "oxyntic cells." This term means that they can be trained according to your normal schedule.
In response to when you normally eat, these cells secrete ghrelin, which makes you feel hungry. Ever wonder why you start to feel hungry at the same time around lunch? It's because of these cells. You normally eat at the same time so these cells act according to this schedule, releasing ghrelin to make you hungry.
Theoretically speaking, when you get acclimated to a period of fasting, there's no stimulus for your cells to secrete ghrelin. Since there's no stimulus, there's no ghrelin and you don't get hungry. Keep in mind, this is theoretical based on how these cells function, but I'd argue the logic is pretty sound.
3. Other factors
There is also the possibility of other factors, some of which we've discussed, such as catecholamines. These hormones actually help to release fat into the blood stream, which can result in metabolism of fat, thus improving body composition.
Additionally, when large amounts of fat are metabolized, this can result in the production of ketones, an alternative fuel source for the body. In essence, fasting mimics a ketogenic diet and a ketogenic diet mimics fasting.
It's also quite possible that these ketones are protein-sparring, meaning you don't really lose muscle (which studies actually indicate this).
Just remember, these are certainly possible factors that set intermittent fasting apart from others. However, the most sound logic currently is that it results in a reduction of calories and thus, results in weight loss. That's not to downplay these other factors as possibilities, it's just to point out that the calorie side of the equation is the most likely and practical theory behind intermittent fasting's effectiveness.
Originally, it was thought that you could just constantly stimulate protein synthesis and thus, grow constantly. As it turns out though, even if you were to intravenously inject amino acids, this process stops working. Unfortunately, there is a refractory period where even if amino acids... are present in the blood, the process of building new proteins still stops.
Potential Issues With Intermittent Fasting
1. There is a transition period.
As with other diets that radically change your routine, there is an adaptation period to fasting. This means you can expect to feel like shit for a couple days during the fasting period. Although, much of the fasting period will be during the night so it's not as bad as the typical keto transition period.
To combat this, I suggest starting with a shorter fasting period, such as 12 hours and increase that duration when you can. For example, you can start the fast at 9 p.m. after your last meal and then fast until morning at 9 p.m. Realistically, that's pretty easy and you might be doing it already. As you become acclimated, increase the fasting period by an hour until you reach your desired duration.
2. You can potentially reduce your muscle building response.
The leading theory behind muscle growth is inducing protein synthesis, often.
Protein synthesis is a rate of synthesizing new, contractile proteins which make up muscle fibers. Theoretically, the more often you can stimulate this process, the higher the chance you'll have of building muscle. However, it's a bit more difficult than that.
Originally, it was thought that you could just constantly stimulate protein synthesis and thus, grow constantly. As it turns out though, even if you were to intravenously inject amino acids, this process stops working. Unfortunately, there is a refractory period where even if amino acids (protein, such as chicken, broken down into its constituent parts) are present in the blood, the process of building new proteins still stops.
This means that over the day, you need to have peaks and valleys of amino acid availability (or period periods of eating and not eating) in order to optimize the process of protein synthesis.
When you fast and reduce the time period of eating, you also reduce the amount of time you stimulate this process.
Anecdotally, many people don't have issues with putting on muscle, but it's hard to tell. Personally, when intensely trying to put on muscle, I stop using intermittent fasting. Just keep this in mind if your goal is to maximize muscle mass.
3. It's easy to under eat
Again, anecdotally, it's quite easy to under eat. Since you spend a lot of the time not fasting, and you do so while not being hungry, it's quite easy to not consume adequate calories.
It's suggested that you track your intake to ensure that you're consuming enough calories for your needs, especially if you're very serious about adjusting body composition.
4. It may not be optimal for athletes
Piggy-backing on the last point, intermittent fasting may not be optimal for athletes that require constant nutrition.
Again, this will largely depend on preference. Just keep this in mind if you depend on your ability to perform at high intensities, long durations or both.
Adjusting Fasting According To Training
I've written and spoken about this a couple times, but considering the nature of this post, I wanted to mention it again.
I strongly believe that you should adjust fasting based on your training. As I mentioned earlier, protein synthesis is the best current theory regarding muscle growth. This process is up-regulated in response to resistance exercise, hence the whole idea of an "anabolic window."
However, consider for a moment if you fast every day. Depending on when you exercise, you may experience a long duration (the rest of the day) in which protein synthesis is elevated (I.e. you train in the morning or around noon) or that period could be quite short (you train in the evening).
Thus, if you train in the evening, it may be in your best interest to abstain from fasting the next day.
My reasoning for this is that if you train at night, and eat after you train, you're only allowing a fairly short amount of time for muscle growth to occur. If you finish training at 7 p.m. have your last meal at 9 p.m. and then wake up the next day, you muscle building "window" so to speak is quite small.
If you train at noon and start eating at 1 p.m., you in essence have 8 or more hours to ingest food. That's a big difference in my opinion.
Because of this, if you train at night, it may be in your best interest to NOT fast the following day.
For more in depth guidance on this subject, please head over here and here to learn more.
Should You Use Intermittent Fasting?
As will be stated multiple times in this series, the use or disuse of a dieting style should be 100% based on your personal preference.
As a personal note, intermittent fasting is easy. I wake up, have coffee and don't eat, simply because I'm not hungry. That last point is important because many people argue you should eat even if you aren't hungry. Bullshit, I say.
Keep in mind that there isn't anything magical about breakfast. Breakfast is no different than any other meal, just because of the time it occurs. I've said this multiple times and I truly believe it: unless breakfast allows you to have better control of your appetite and food intake later in the day, eating it or not eating it makes zero difference.
If breakfast allows you to control hunger later in the day, go for it. If it doesn't then you're just consuming extra calories with no benefit.
Decide for yourself and follow your own preferences.
1. Won't I lose muscle?
With any calorie restrictive diet, muscle loss is possible. However, most research on intermittent fasting indicates that doesn't really occur.
Regardless, special care should be taken and you should ensure you're consuming adequate protein to help avoid any potential loses. Just know that intermittent fasting won't directly lead to muscle loss. If it did, no one would use it.
2. How should I eat?
Intermittent fasting does allow you to be a bit more lenient with your food options.
However, if you want rapid progress, I suggest maintaining high quality food intake. Additionally, intermittent fasting works quite well as a flexible dieting approach as well. I've written extensively on the subject, so please read my full length article on the subject.
3. Should I eat before training?
This is largely personal preference, but you SHOULD have at least some nutrition around the workout, either before or after.
I personally suggest having a protein shake before training, regardless of fasting. If you can't stomach whey (or other styles of protein powder) consider having a BCAA supplement.
4. Do I need BCAAs during the fast?
No and in fact, you shouldn't consume them. If you're that worried about muscle loss, consider a different style of dieting.
5. Can I consume coffee and such while fasting?
This depends on your purpose. If you fast for health effects (outside of the scope of this article), it will be up to your discretion. Otherwise, yes. I consume copious amounts of coffee while fasting. Not to mention, the fasting period will likely improve your coffee's effectiveness.
6. When do I start/stop my fasting period?
I follow a 16:8, fast feed schedule. On a perfect day, I would start training around the 14.5 hour mark and then begin eating once complete (16 hours) and then eat until the 24 hour mark, at which point, the next fast begins. Here's an example:
7. What about if I exercise in the morning?
You have two options here:
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