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Fact checked by Andrew Lenau, ISSA CPT & Sports NutritionistFACT CHECKED
May 16, 2022
Fasting has become an extremely popular diet method to not only lose weight, but also to improve sports performance. While there are some ardent followers on both sides, the fact remains that fasting does have science backed benefits and can help lose weight. There are also proven benefits to working out fasted. We’ll talk about fasting below, but what we really want to address is a common question: ”Will pre-workout break a fast?"
A lot of people want to workout fasted, but they also want to drink a pre-workout beforehand to ensure they get a great workout in - it’s a double whammy on the fat loss front, right? The issue is, it’s actually hard to get calorie info on pre-workouts as it is technically a “dietary supplement”, so brands can’t have calories listed on their nutrition facts label. That said, the amount of calories in most pre-workouts is very minimal.
On a side note, some brands don’t even have all of their ingredients and dosages listed (we don’t like those types of pre-workouts - if it doesn’t have all of the ingredients with exact dosages on the label, it’s just a cheap standard blend!).
If the ingredients are listed on the label, then there are some key ingredients to look out for that can break a fast, which we will go over.
We hope this article will answer your questions. No more wondering if you are actually fasting or not.
In this article, we are going to cover:
Let's find out if your favorite supp has wasted all those times you trained hungry.
There are quite a few benefits from fasting that are supported by evidence. We specifically care about those that fall under one of two categories: weight management (weight loss or weight maintenance) or sports performance.
Here's a non-exhaustive list:
The most basic definition of fasting is ‘willingly choosing not to eat and/or drink’.
The two primary reasons being:
As we are concerned with fitness and training, we're only going to speak about fasting as choosing not to eat food for the purpose of health and fitness. We will look at the physiological effects pre-workout has on the human body, not if it breaks a religious code.
As a side note, there are different methods of fasting (time periods), and types of fasts, such as no calories or no food and water - p.s. going on an extended water fast while training is really stupid. Don’t do that.
We won’t get into the nitty gritty of fasting methods, as we really just want to focus on if pre-workout will break a fast, and if so, how and why. Regardless, this will apply to any type of fast, so it doesn’t matter.
What we will do is look at the physiological effects of fasting…
While you could say that anytime you're not eating, it is "fasting," the technical term is dependent on what happens physiologically. There have been several different attempts to describe when "not eating" becomes "fasting.
For example, one simple definition is when your body has completely absorbed a meal and fully digested it. This works on a basic level but to answer the question of "does pre-workout break a fast?", we need a little more technical of an answer.
For that, the best description is probably given by the famous fasting and metabolism researcher Dr. George Cahill. In his monumental study, he laid out 5 stages of fasting that he was able to identify1. These stages are based on the body's transition to different sources of fuel, specifically glucose from carbohydrates and triglycerides from fats.
Our bodies' preferred source of fuel is glucose, as it's readily available and easy to process. However, as glucose becomes depleted in the body, the body will start to rely on triglycerides as the human body holds a large amount of fat.
With that understanding, here are the 5 stages of fasting:
Keep in mind that these time frames are for sedentary people. High intensity exercise can deplete our glucose and glycogen stores much faster.
So as we see, when people are asking, "does so-and-so break a fast," they are really asking, "Will the food they eat disrupt this transition of metabolic energy sources?" This is actually kind of hard to answer because it really depends on what stage of fasting they are in as well as what they consider fasting. As you see, fasting rests in a continuum.
In the fitness world, the vast majority of people asking this are using intermittent fasting, meaning that the vast majority of people aren’t fasting any longer than 20 hours. As you can see above, that’s barely getting into the 3rd stage so this population isn’t really doing hardcore fasting.
The most important factor to this question is going to be what your pre-workout contains or what ingredients it consists of. As you likely know, a pre-workout can contain a wide variety of different compounds. Some of these could break a fast, and some couldn't. So instead of answering if a pre-workout will break a fast, we'll look at some common ingredients and see what they do.
The pre-workout ingredients of most concern in terms fasting are:
We should also address one issue real quick first. One of the benefits of fasting is a process known as autophagy, which is basically your body's recycling system. It's when your body eats old cells and creates new ones. Some doctors or practitioners who take fasting very seriously will say that drinking anything other than water will break a fast because it can disturb the process of autophagy.
So…there's that. But this shouldn't even be a concern unless you fast for longer than 24 hours, as this tends to be the minimum time requirement for this to start. Again, as the vast majority of people reading this are likely on some form of intermittent fasting, this probably isn’t much of an issue.
If your preworkout contains caffeine, you are good as caffeine DOES NOT break a fast. While there may be minimal calories, it's generally not enough to have any massive effect on your energy utilization or cause a spike in insulin.
Yes. Sugar DOES break a fast. In fact, this is probably the worst food to break a fast with as it will cause a massive sugar and insulin spike. No. Just don't.
So you might think you're ok with artificial sweeteners, but actually, this is up for debate. Studies are contradictory, and while most show that artificial sweeteners don't cause a spike in insulin, there have been some that do show a spike, mainly in regards to sucrose and saccharin2-3.
Interestingly, this rise in insulin doesn’t seem to be directly from the sweetener itself, but what's called a "cephalic phase insulin release". This is when your body raises insulin in anticipation of eating so it seems that the taste of these can cause an insulin spike since they mimic sugar.
Therefore, if you don't want to break a fast, definitely stay away from the two aforementioned artificial sweeteners.
Still, if you definitely don’t want to break a fast and want to be 100% positive you won’t, you might want to stay away from all artificial sweeteners, so there goes basically every pre-workout.
One of the biggest misconceptions is that amino acids don't have calories. Lies! We don't care what the nutrition label says; it's a lie! Let us explain, and it will make sense real quick.
Obviously, this is silly. The problem is that a nutrition label can only assign calories to whole protein. Since amino acids aren't a whole protein so nutrition labels can't label them as protein. Therefore, you can have BCAAs or EAAs with “0 calories” listed.
The 9 Essential Amino Acids:
The ones with an asterisk (*) are BCAA's. If you see any of these on the pre-workout label, it will contain some calories.
How many calories do BCAA's have?
Surprisingly, your BCAAs actually have a bit more calories than whole protein. A study reported that leucine has 4.65 calories per gram, isoleucine has 4.65 calories per gram, and valine has 4.64 calories per gram4. So basically, every 10g of BCAAS has around 46 calories!
Further, while it can sometimes be exaggerated and called a "spike," BCAA's can, in fact, cause your insulin to rise. So this is going to depend on why you're fasting and what you consider "breaking" a fast.
If the pre-workout uses artificial sweeteners and doesn't contain BCAA's, it is likely to have zero calories (or a very minuscule amount). However, there are some exceptions depending on what other ingredients are in your pre-workout, but for most pre-workouts, 0 calories holds true.
When it comes to vitamins and minerals, they do not provide any calories, even though they are essential nutrients.
But again, you have to remember that even though a pre-workout may have zero calories, the artificial sweetener may still cause a spike in insulin, which affects a true fast.
As mentioned before, we are looking at this question in the eyes of most fitness enthusiasts who use intermittent fasting for weight loss or sports performance. Also, we are making two assumptions before we give our verdict:
With that in mind, we don't think a pre-workout is really going to cause any negative effects on the adaptations you're looking for when fasting. The reason we give the minimum of 8 hours is that we want your glucose and glycogen to be extremely low. Being so, even if you do take a pre-workout with a few calories, it still isn't going to make a huge dent in your metabolism.
Further, we are going to assume you will eat after your workout; which is assuming you’re going to workout after you take your pre-workout. There’s a lot of assuming going on. Regardless, if you are going to eat after your workout, then that means you’re near the end of your fast anyways ,so you’re not really going to disrupt anything that won’t be disrupted in another hour or so.
However, if you are fasting for reasons other than what we mentioned or are concerned about being on a "true fast," pre-workouts probably aren't the best choice. After reviewing all of the evidence, as well as looking at the opinions of fasting experts and followers, there seems to be contradicting information and answers. Therefore, you should probably stay away if you don’t want to take any chances of pre-workout breaking your fast.
We're going to flip the script real quick and suggest that a pre-workout might actually be good when you are fasting. This is primarily due to the caffeine in pre-workout, which can improve your body's use of fat stores for energy.
In fact, this study specifically found that after fasting, caffeine can "effectively increase" fat utilization5. We should mention that this was during aerobic exercise, but in our opinion, aerobic exercise is the most effective form of exercise to use with fasting (fasted cardio). Therefore, we feel confident to say that pure caffeine is the best pre-workout for fasting.
So that's about it. While we don't feel a pre-workout is going to have any negative effect on fasting for weight loss or performance, you should probably stay away if you're doing a true fast. You don’t want to take any chance of your glucose rising (tricked into it or not).
If you want to take pre-workout while fasting, and you aren’t so worried about some tiny effects that may occur, then just stay away from pre-workouts that contain any of the 9 essential amino acids, sucrose, or saccharin. All other ingredients should be fine.
If you're still concerned, you could always just pop some caffeine pills, enjoy the increased fat oxidation, and be confident you're still in a fast.
If you are fasting as a way to lose weight, consider finding a pre-workout supplement for weight loss with the right ingredients to support your goals.
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