Many moons ago when I first decided I wanted to transform my body, I stumbled upon the idea of fasted cardio in a book. Yes, a book, because back then the internet was still new and awesome fitness sites like this weren’t around to disseminate good fitness info to the masses saving them from doing the dumb shit I did. (You’re welcome.)
So, anyway, as I was saying–I find this book and the book claims if I do fasted cardio I’ll force my body to burn stored fat which would turn me into a “fat burning furnace” or something.
Of course, at the time this made sense to my younger, naive, misinformed self: I want to burn body fat and fasted cardio increases fat burning. So if I train fasted…1+1= Fat loss. Simplez.
The next few weeks involved waking up at the butt crack of dawn, mumbling curse words at my alarm clock, slipping on my trainers, and going for a run.
To cut a long (and insanely boring) story short–nothing happened. I didn’t lose fat; the only thing I lost was hours of precious sleep.
That was almost a decade ago, and yet, I still see people espousing the benefits of fasted cardio. Back then it was numbnuts writing fat loss books, today it’s Instagram “Influencers”–same shit, different toilet.
As you’re about to learn, you probably don’t need to be doing fasted cardio (or any form of fasted training) if you want to lose fat.
Let’s get into that.
Quick note: throughout the article I’ll be using the term ‘fasted training’ to refer to both fasted cardio and fasted strength training.
What is fasted training?
Before we get into whether fasted training is better for fat loss, we need to understand what’s meant by ‘fasted’ training.
You’re always in one of two states:
1. Fed (or “postprandial” if you wanna swing your nerd boner around)–when you eat food, your body is in a fed state where it begins to digest the food you’ve eaten. If you eat before exercise, your body will use the calories from that meal as energy.
2. Fasted (or “postabsorptive”)–if you haven’t eaten anything for a while, you’re in a fasted state. If you train fasted your body will revert to its own stores for energy.
With this in mind, fasted training makes sense. If you want to lose fat, exercising in a fasted state will force the body to use its own stores for energy and in turn, you’ll burn more fat, right?
Eh kinda. But, also no.
While it’s true that fasted training increases fat oxidation this doesn’t translate to increased (body) fat loss.
This is where a lot of the confusion stems from, so let’s understand what fat oxidation actually is.
Fat oxidation is just a fancy word for ‘fat burning’ and consists of two steps:
Your body is constantly storing and oxidising (burning) fat throughout the day.
For example, you wake up in the morning, skip breakfast and go to work. At this point, your body is oxidising stored fat for energy.
Later in the day, you eat lunch. Now your body has stopped oxidising stored fat and is using the calories from your lunch as energy.
After a few hours, your lunch has been digested and you’re back in a ‘fasted’ state–your body starts oxidising its own stores again for energy. When you eat dinner that night, your body begins this whole process again and by the time you wake up in the morning, you’re back in a fasted state (until you eat again).
This isn’t exactly mind-blowing stuff. You eat, your body uses the calories from that meal for energy. You don’t eat for a while and your body runs on its own stores for energy. Our body’s ability to do this is why we don’t end up incapacitated half-way through the day if we haven’t eaten for a while.
Because of this fact, people assume if they train fasted they’ll burn more fat by forcing the body to use its own stored energy.
The problem with this idea is that short-term fat oxidation (burning) doesn’t mean jack for fat loss and it’s the long term balance–over days and weeks–that will dictate whether you’re losing or gaining body fat.
If the amount of fat you burn stays the same as the amount of fat you store over the long term: body fat remains the same.
If you burn more fat than you store: you’ll lose fat.
If you store more fat than you burn: you’ll gain fat.
This is referred to as ‘fat balance’ and is dictated by your total calorie intake. So sure fasted training may burn more fat than if you were training fed but if, at the end of the day, you’re still in a calorie surplus (because you’re eating too many calories)–no amount of fasted training is going to help.
And so, it’s not surprising when we look at studies into fed versus fasted training for fat loss, there’s no difference.
In this 2014 study:
Researchers assigned 20 young healthy females to one of two groups:
Both groups were in a 500 calorie deficit and performed 1 hour of steady state cardio 3x per week for 4 weeks.
Both groups lost weight and reduced their body fat percentage but there were no significant differences between groups.
Another study investigated the effects of fasted versus fed interval training on fat loss.
Sixteen women were assigned to either a fasted group or fed group and performed three sessions of HIT cycling over 6 weeks.
Researchers concluded: “Short-term low-volume HIT is a time-efficient strategy to improve body composition and muscle oxidative capacity in overweight/obese women, but fed versus fasted-state training does not alter this response.”
But, wait! There’s more.
A meta-analysis published in 2017 summed up the current research on the topic.
The analysis consisted of 5 studies comparing fasted to fed exercise and totalled 96 participants.
With researchers also adding:
It’s important to note the current studies we have on fasted training for fat loss are still fairly limited and short-term. Maybe with longer-term studies, we’ll uncover an advantage.
But until we have those studies, we can only go by what we currently know–fasted training doesn’t show any benefits for fat loss over fed training.
At the end of the day, what matters most for fat loss is your total calorie deficit. Whether you train fasted or not comes down to personal preference and scheduling.
Do you prefer or enjoy training fasted? Then train fasted. Do you have to train early in the morning and have no choice but to train fasted? Then train fasted. Do you find you’re not hungry in the morning and eating before a workout makes you nauseous? Then, yep you guessed it, train fasted.
With that said, let’s address two common concerns people have about fasted training.
Concern #1: Will fasted training negatively affect my performance?
A 2018 meta-analysis looked at 23 studies on fed versus fasted cardio and found no difference when workouts lasted less than an hour. The researchers did note when workouts lasted more than an hour, eating before the workout improved performance.
Aadam, fuck cardio–what about strength training?
The research here is limited and conflicting.
An interesting study from 2013 looked at the effect of fed versus fasted resistance training during Ramadan in recreational Muslim bodybuilders.
At the end of the study period, both groups maintained their training volume and didn’t report any changes in rates of perceived exertion (how difficult the session felt).
If you’re not familiar with Ramadan fasting, let me fill you in real quick: the fasting period can last up to 20 hours with no food or drink (including water). The men in the study worked out between 4-6 pm, so they were fasted for about ~15-16 hours before training and still managed to perform without any impairment.
This isn’t too hard to believe once you understand the physiology. When you train, your muscles use muscle glycogen to fuel the workout. Even after an overnight fast, muscle glycogen stores aren’t depleted (unless you ran a marathon during the night and went straight to the weight room. In which case, congratulations you’re a God among us mere humans) so you have sufficient stores to fuel your workout.
Multiple other studies have also failed to show an improvement in resistance exercise performance when the participants were provided with carbs before and during training versus no carbs before or during.
Like I said, the research is conflicting. Seeing that science isn’t being very helpful, here’s my stupid simple recommendation:
- Does fasted training negatively affect your performance? Then have a small snack in the morning before your workout (carbs+protein).
- Do you feel fine training fasted? Then train fasted.
It’s important to mention when someone thinks their performance is suffering because they’re training fasted, often times that’s all it is–a feeling.
We’ve all had days where we’ve felt tired, maybe we had a long day at work and couldn’t get a meal in before the workout but crushed the workout anyway. Conversely, we’ve all had days where we felt great, were well fed but the workout sucked.
I bring this up to make you aware of the self-defeating prophecy–if you’re training fasted and you assume you’ll be weaker, then that’s exactly what will happen. The placebo (or in this case, the nocebo) effect is a very real phenomenon.
So, I dunno, think happy thoughts click your heels and go lift some weights, maybe? In most instances, if your workout lasts less than an hour and you’re not performing high amounts of volume–you’ll be ok.
I’m also not saying you should train fasted, for most people eating something prior to training is probably a good idea. But if you absolutely must train fasted, this is something to keep in mind.
Concern #2: will I lose muscle if I train fasted?
Short answer: No.
Long answer: No.
Remember those Ramadan bodybuilders from like three paragraphs ago? Well, despite the fact they lifted weights after a ~15-16 hour fast, they didn’t lose any muscle mass.
In another study, also done during Ramadan, the fasted participants who engaged in cardio didn’t lose any lean mass by the end of the study period.
If that’s not enough, here are two more reasons why you don’t need to worry about fasted training causing muscle loss.
And as I pointed out earlier, even after an overnight fast–you have sufficient glycogen stores.
Now, I know what you’re thinking–but Aadam, I train soooo hard, I’m straight beast mode all day errday, I must be burning through my glycogen stores.
Yeah, probably not.
In a study by Tesch et al., nine bodybuilders performed five sets of front squats, back squats, leg presses, and leg extensions to failure. After these poor souls went through squat hell and back, the researchers took biopsies of the muscles and compared them with the biopsies from before the squat-fest.
Muscle glycogen had reduced by 26%.
For context, we store about ~500 g of glycogen in our muscles. Seeing the participants only trained their legs, let’s assume the number is ~250 grams. A 26% reduction would be ~65 grams. Yes, even after all that squatting the participants only burned through 65 grams of glycogen.
So unless you’re planning on spending your entire day in the gym (probably don’t) or running an Iron Man every day (definitely don’t)–you aren’t depleting your glycogen stores to an extent where muscle breakdown will be a concern.
2. Net protein balance
Your body is constantly building (muscle protein synthesis) and breaking down (muscle protein breakdown) muscle tissue in a 24-hour period.
Whether you build or lose muscle depends on the net protein balance over the long-term.
If the rate of muscle protein breakdown exceeds the rate of muscle protein synthesis–you’ll lose muscle.
If the rate of muscle synthesis exceeds the rate of muscle breakdown–you’ll maintain or build muscle.
Which is why you don’t need to worry about the short-term breakdown or build up of muscle, like during a workout. You need to be more concerned about the net protein balance over a number of days.
Also, and people forget this, strength training is inherently anabolic–it has muscle preserving effects.
Here’s what I mean. Take a look at this image.
When you’re resting in a fasted state (a), you’re in a negative protein balance–muscle protein breakdown is higher than muscle protein synthesis. If you’re resting but consume protein, you’re in a positive protein balance (c)–muscle protein synthesis exceeds muscle protein breakdown.
Now take a look at the second bar (b)–even though fasted training still keeps you in a net negative protein balance, the rate of muscle protein breakdown is reduced compared to resting in a fasted state. This is because strength training increases both muscle protein synthesis and muscle protein breakdown and once you consume protein, ideally within an hour of finishing the workout, you’re back in a positive protein balance (d).
As long as you’re consuming some protein around the workout period and an adequate amount of protein by the end of the day, you don’t have to worry about muscle loss when training fasted.
My suggestions if you’re training fasted:
• Ideally try to consume ~20-30g of whey protein before the workout as a minimum.
• If you can’t, or don’t want to eat before training then aim to get at least ~20-30g of protein within an hour of finishing the workout.
• If you find your performance is impaired, try taking some caffeine pre-workout.
• Skip the BCAAs because they’re worthless. You’re better off consuming a protein shake.
• Consume adequate water leading into, and throughout, the workout.
Hold on, what about fasted cardio for stubborn fat?
Ah yes, the stubborn fat chestnut. While fasted cardio could, potentially, have some benefits for burning stubborn fat, 98% of you reading this don’t have a stubborn fat problem, you just have a fat problem. So, instead of worrying about fancy protocols and exotic fat burning supplements, get your diet and exercise in check and focus on reducing total body fat.
I’ve worked with hundreds of clients and I can count the number of these clients who actually had a stubborn fat problem on one hand.
- Fasted training isn’t superior to fed training and if your goal is fat loss, instead of worrying about whether you should train fasted or not, be more concerned with your total calorie intake.
- If you enjoy training fasted or your schedule only permits training early in the morning, then train fasted.
- Performance shouldn’t be negatively affected if you’re training fasted but if you find it is, then consume a small high-protein snack ~30 minutes before to training.
- No, you won’t lose muscle if you train fasted.
- If you are training fasted, try to get ~20-30g of protein within an hour of finishing the workout.
- Unless you’re already ~10% body fat (men) or ~18% (women)–you don’t need to worry about stubborn fat.
Want to learn more about fasting? Download my free fasting guide here.
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