What you need to know about fasted workouts
Fasted workouts. What are they? How do they work? Why do people love them? And why are other people hating on them? Should you start doing them? So many questions! Thankfully I've rounded up as much info as I could to find all the answers — and then some.
What is a fasted workout / working out fasted?
It's a pretty simple concept — any exercising while in a fasted state — aka 8-12 hours after your last meal. That's literally all there is to it. Typically this is done in the morning before eating your first meal and most commonly done as cardio. "Fasted cardio" has been a popular fat loss strategy in the bodybuilding community for years - which could be one of the reasons it gets such a bad reputation. Bodybuilding isn't exactly known for it's sustainable and overall health focused habits if ya know what I mean.
Why is it so popular?
Disordered tendencies aside - fasted workouts train your body to burn stored fat which can help you loose weight. How does this work though?
Your body needs carbohydrates to survive - glycogen more specifically. After you eat a meal, your body breaks down the food you consume. It stores what it can in your muscles as glycogen - although space is limited and muscles can only hold so much at one time. The rest is stored as fat for later use. Throughout the day — exercise or not —your body will use up the stored glycogen. Because storage is limited the previous thought process was — feed your body a constant stream of calories so you don't run out of energy. What recent research is finding however is that when glycogen sores are empty - it has a back up plan. Fat. But it will only go there if it is 100% out of glycogen. Hence the fasted state.
But I've heard that working out fasted will break down muscle tissue.
Yes it's true - in extreme circumstances it is physiologically possible for your body to break down it's own muscle tissue [amino acids] and convert it to sugars [glucose] to use for energy. It's called Gluconeogenesis.
Your body is probably going to burn fat first.
As it turns out — although it is possible to convert amino acids to glucose — it's not easy. And it's not going to be the body's first choice. Fat is not only more readily available, but it provides more return on investment. Fat contains 9 calories per gram compared to the 4 calories per gram in protein [amino acids].
If fat is so high in energy why don't we burn it more easily?
True - fat is higher in energy. And while carbs also net 4 calories per gram [the same as protein] when it comes to CREATING energy carbs are easier to use than both fat and protein. Grab and go. Think about all the times you probably grab a granola bar out of the cabinet for a snack because it's ready to eat versus making a veggie and hummus platter. One of those might be better for you in the long run but the other one is super easy. So carbs are the number one source of energy for the body because - well they are super convenient. Make the body work a little harder and you'll train it to use fat. Make it work even HARDER and it will start to use protein.
How much you're eating in a day DOES matter.
It's important to consider that restricting calories - no matter what time of day you workout - can be one of the leading factors that determines if you're body starts to burn fat or break down muscle. So if you've been restricting calories for a prolonged period of time — you're probably at higher risk for your body breaking down muscle than if you workout fasted.
My personal experience.
Before I ever started diving into an intermittent fasting lifestyle I'd been doing fasted workouts for about a year. During the week evening workouts fit my schedule better, but on the weekend I would always find a spin or yoga or barre class to squeeze into my morning. Not being hungry in the mornings anyways — I started skipping breakfast and heading right to class. opting to just eat after class. I never found this to affect my strength or performance. I've never felt weak or dizzy or lightheaded. In fact a lot of the time I feel more energized and more in tune with my body.
Now with my return to running, and intermittent fasting lifestyle - I've been extra curious about how my body would react to fasted training. To my surprise it's been great. Not only do I feel just as energized, it also cuts my get-ready time in the morning drastically. A few sips of coffee and water, a change of clothes and I can be out the door in 20 minutes.
Take it from a registered dietitian
My opinion alone may not be enough to convince you I'm not doing my body major damage.- luckily I have some friends who just so happen to know a thing or two about nutrition. Angela Piptone R.D is not only a metabolic dietitian but also a fellow marathon runner who does most of her marathon training fasted. "Obviously no one should run a (full) marathon fasted but I think a few miles is totally harmless if it feels good. Ive been running 90% of my runs fasted for the past 5 years and have definitely gained rather than lost muscle." She also goes on to explain that while everyone is different and it may not work for everyone — there certainly is no harm in trying.
So should you give it a try?
If you are currently using calorie restriction as a weight loss strategy - I would not recommend diving right into a fasted workout. As I mention above this could cause your body to breakdown muscle.
However if you are not in any kind of calorie restriction I say giving it a try is fair game. Just keep in mind — as with any new habits — to take small steps to get to the larger goal. If you regularly do a very high intensity workout early in the morning and are used to eating a meal beforehand I wouldn't recommend skipping breakfast and expecting to get the same results. Switch out high intensity workout for something steady state to get your body used to the fat burning process. If that feels manageable slowly increase the intensity over time.
At the end of the day do what you are most comfortable with, and what you can make a long term habit. If you can't stomach running on empty – then don't! If you do like it - great! Be aware of what's going on with your own body and stop if anything feels uncomfortable.
Do you ever workout fasted? Have you tried it and it wasn't for you? I want to know!