Intermittent fasting brought up a new argument to the fitness world, do you still need to fuel before a workout? Before intermittent fasting (IF) became extremely popular, many people resorted to pre-workout snacks or other supplements like pre-workout, BCAA's, protein powder to help fuel their workouts. Although many still do this, and there's nothing wrong with doing so, more and more people are trying a new approach: Fasted workouts.
This approach doesn't exactly mean exercising on an empty stomach. Although that is the case, it specifically refers to working out in a fasted state, which can occur naturally when one is intermittent fasting. For those who don't know, this is a time approached eating pattern that involves organizing your eating between a certain amount of hours. Meaning your fasting for 16 hours or more at a time. Many like this form of eating because it has been known to help with lowering blood sugar levels, increasing energy, reducing inflammation, and aiding in weight loss. There are various fasting methods, but 16:8 (having an 8-hour feeding window, and fasting for 16 hours) is the approach most people do for weight loss and training purposes.
Intermittent fasting and exercise seem like they wouldn't be compatible considering that having no fuel in your tank means your body's energy is running empty, which most likely means there will be a decrease in performance. This makes many wonder if it's even worth trying? Well, that depends on you! Although a decrease in performance can happen, it all depends on how you approach it. We'll give you all the info you need to decide whether fasted workouts are worth it for you or not by giving you the facts on its benefits, potential downfalls, then we'll go into the nitty-gritty. How to approach it for your goals to make sure that you're maximizing your workouts, not the opposite!
As mentioned earlier, fasted training means to workout in a fasted state. But exactly how long do you have to fast to be in that state? For those who don't practice intermittent fasting, it can be anywhere between 8-12 hours. It really depends on how big your last meal was and how fast your digestive system works. That's because in order to be in a fasted state the body must have stopped breaking down food in order for insulin levels to be low, and for there to be no glycogen - fuel - in your blood. That means that when a person has a fasted training session in the morning before their breakfast their body turns to another source of energy - Fat.
So those are the basics of fasted training! You don't even have to practice IF to do it, in fact, if you already do an early morning workout on an empty stomach (depending on how late and big your last meal was) you're already doing working out while fasting, without even realizing it!
This might surprise you, but for years bodybuilders have used fasted workouts as a technique to maximize fat loss. Specifically fasted cardio, not fasting, and lifting super heavy weights. That's because they need to approach their workouts based on their goals to gain serious muscle mass. So yes, it is possible to practice intermittent fasting and exercise while still being able to build muscle, but before getting into this, let's discuss the benefits of fasted workouts. AKA the reason so many gym-goers are now adopting this method.
1. It maximizes fat burning
If you really want to maximize your cardio sessions consider doing it in a fasted state. The main purpose of training in a fasted state is so there is no glucose in your bloodstream that way your body turns to fat stores in order to use fat for fuel. In fact, one study in particular shows that not only do fasted workouts burn more fat, it can also increase the amount of fat that's liberated from your cells.  Although there are studies that had similar findings, others show no difference between working out fasted or in a fed state. When it comes to decreasing overall body fat, it really depends on how you're training and your diet and lifestyle.
For those who practice a keto diet or have been doing IF for a longer period will benefit more from fasted exercise because their body is already adapted to using fat for energy so the body immediately knows what energy source to go to, thus making it easier for them to burn fat instead of another source like muscle.
2. Increases growth hormone
Another reason fasting might help build muscle and promote weight loss is because of the human growth hormone, or HGH. This hormone is released by your pituitary gland and it has pretty impressive responsibilities in your body, like: helps make new muscle tissue and burn fat, boosts muscle, bone, and cartilage growth which reduces the risks of bone fractures, and boosts the body's ability to break down glucose without using oxygen.
The thing about this hormone is that it tends to slowly decline as you age, and one way to increase it is by fasting! A study published in 2011 shows that 24 hours without food increased HGH production by 2,000% in men and 1,300% in women.  But unfortunately, the effects end when the fast is completed, and obviously, you can't fast forever since you have to refuel for your workout eventually! One way to keep muscle-friendly hormone levels up like this one is by regularly fasting.
3. Increases VO2 Max
Fasted cardio can help with your endurance by increasing your VO2 Max. Your VO2 Max is the maximum amount of oxygen your body consumes during an aerobic exercise when you're working your hardest. And in case you didn't know, your endurance is only as good as your body's ability to bring oxygen cells. So doing a fasted cardio workout can increase your ability to take in oxygen and deliver it to your muscles in order for you to work harder! To go in further into that, a study in the Journal of Science and Medicine in Sports found that healthy untrained men and women had a significant increase in their VO2 Max when they trained in an overnight fasted state compared to when eating a small carb-filled post-workout snack. 
Sadly, nothing is ever perfect. As with any training technique, there are cons to fasted exercise that we have to tell you in order for you to decide whether it’s right for you to try.
1. Potential muscle breakdown
Essentially with fasted workouts, the body uses fat for fuel, but it can also go to another fuel source, like your muscle tissues. Meaning instead of using fat from your adipose tissue, your body might use the protein that makes up your muscle instead. One particular study compared to groups, one that did one hour of steady cardio in a fasted state and one that did non-fasted cardio. The results showed that the fasted group had twice the amount of muscle protein breakdown compared to the non-fasted group. 
So if you're strength training to promote muscle gain then muscle loss is clearly something you don't want to happen. But don't overlook fasted cardio/workouts just yet! Whether your body burns fat or muscle depends on the what type of exercise you do - Don't worry we're covering this in the next section 😉
2. Might decrease performance
It should come as no surprise that fasting might get in the way of how hard you train. Most people are used to eating before an intense training session so their bodies are accustomed to that steady flow of fuel. When you just get started with fasted workouts you might notice a dip in your energy due to your glycogen stores being empty. It can take time for your body to get used to not receiving its usual steady flow of fuel. Even if you do become adjusted, you might still feel a difference between your fasted and non-fasted training. That's because although fasted workouts increase your VO2 Max, your body is still missing that fuel to burn.
Again, it all comes down to the type of exercise you do while you're fasting. These are two downfalls that can be avoided if you approach it safely and the right way.
How to approach fasted workouts for your fitness goals
In order to approach fasted workouts the right way, you must know when intermittent fasting with exercise works and when it doesn't. So let's break it down by two fitness goals: fat loss and muscle building.
Fasted workouts for fat loss
Jim White, R.D.N., an ACSM exercise physiologist says that the best fasted workouts for fat loss are typically low to moderate intensity (stay between 50-60% of your target heart rate) workouts like walking, jogging, elliptical, etc. Keeping the workout at an easy to moderate pace will increase the chances of your body using fat.  But, you should still lift. Even if your main goal is losing fat, lifting will help prevent your body from burning muscle to fuel daily activities. On the upside, since you're not training to pack on muscle you can keep your strength training workouts between 2-3 times a week. A good schedule would be to do your fasted cardio in the morning and lift in the evening, or if you're busier just do it on the days you're not strength training.
You can also try to do a fasted lifting session since you won't be lifting extremely heavy. Some people prefer not to due to a possible decrease in performance, but others state the opposite and feel their performance is relatively the same. It all really depends on what you prefer and what works with your schedule, just remember to promote fat loss it's best to keep the intensity on the lower side. Which brings another point... Do you have to give up high-intensity interval training (HIIT) altogether? Look, if you love HIIT then you can still implement it in your training! The best approach to this would be to do a high-intensity workout in a fed state, meaning either on days or a certain time that you're not fasting. Technically it's recommended to avoid high-intensity training when fasting, but it all depends on how you feel. If you feel like doing a light lifting session followed by steady-state cardio while fasting is getting you results and you feel like your performance and energy are at a good level then do it! Everyone's body is different, so just try to find what workouts feel best for you and what doesn't.
Fasted workouts for muscle building
When it comes to building muscle and strength, fasted exercise can get a little tricky. It really depends on how heavy and intense your training is. Considering the goal is to gain muscle, you're probably lifting relatively heavy compared to someone focused on weight loss. You might not be lifting like a bodybuilder, but you can still follow their technique of doing only cardio fasted and doing lifting sessions in a fed state. This technique is used because you don't need to fuel up on carbs to do low-intensity exercise, and that type of exercise like steady-state cardio, runs primarily on fat.
Again, it's entirely up to you! There are many avid gym-goers who feel their performance is fine and don't experience muscle breakdown doing their usual strength training routine fasted. If that's something you're interested in, go about it safely. Prepare for it right by...
- Eating your last meal with plenty of protein and carbs.
- Drinking plenty of water or taking electrolytes.
- Timing your fast so it ends after your workout. This will give your muscles the carbs and protein they need to recover.
You can even use black coffee as a pre-workout if you need something to boost your energy right before your workout! Just listen to your body, if at any point you feel dizzy, weak, dehydrated, stop working out, drink water, or fuel up with whey protein or electrolytes.
So are fasted workouts worth trying?
The evidence is pretty mixed, at the end of the day it comes down to a matter of personal preference and your specific goals. Some people love it because it works with their body and schedule! Others prefer breaking down their sessions into two, one fasted and one fed. Others try it and find that it doesn't work for them. The bottom line is, it's up to you. Just remember to approach fasted training safely to ensure you have a good experience. Even if you don't like it, it isn't the only method to burn fat. Find something else and do what works best for you!