So you’re looking to do an extended fast, maybe 3, 5, 7 or more days. But you’re petrified of losing your gains.
I know exactly how you feel. But fear not, because I’ve come up with some best practices for your workout that will enable you to complete your extended fast while maintaining as much muscle mass as possible.
While on a prolonged fast, lifting weights is necessary for maintaining muscle mass. Keeping the weight moderate to high, volume to a minimum, and heart rate down will keep cortisol levels low and provide the stimulus needed without promoting the breakdown of muscle proteins.
Let’s take a deeper look at how you need to design your workouts for the duration of your fast to ensure you hang onto your gains.
Importance of Being Fat Adapted Before Starting The Fast
Although there isn’t a ton research on the ‘fat adapted state’, it’s thought of as an advanced state of ketosis. Usually it takes 2-4 weeks of keto to reach a fat adapted state. This is where your body has become extremely efficient at burning fat for fuel.
Fat adaptation is more like a scale, and less like a binary state. The longer you’re in ketosis for, the more fat adapted you’ll become.
The more fat adapted we are, the more fat we’ll burn on our extended fast. By burning fat more efficiently, we’ll be able to hang onto our liver glycogen stores for longer. It’s only when our liver glycogen becomes depleted that we risk burning muscle for energy.
Cortisol & Liver Glycogen Metabolism
Understanding the role of both liver glycogen and cortisol production is a huge part of knowing how to lift weights effectively while on an extended fast.
If we allow cortisol (stress hormone) to get too high, we risk breaking down muscle tissue to use as an energy source. Similarly, if when we’re working out we engage the anaerobic energy system (high heart rate and exertion level), we risk shifting from fat burning mode to glucose burning mode.
This is a problem because when we’re fasting we’ll quickly deplete our liver glycogen stores, at which point our body will look for other ways (muscles) to get this glucose.
This is why it’s crucial we use the aerobic energy system (low heart rate and low exertion) which can efficiently burn fat for energy as opposed to stored liver glycogen, allowing us to spare our muscles.
Control Cortisol As Much As Possible!
When on a prolonged fast, cortisol levels will go up, it’s inevitable.1https://academic.oup.com/jcem/article/90/2/741/2836628
This is the unavoidable reality. We don’t know exactly how elevated the cortisol level needs to be for the body to start breaking down muscle, but we do know that it’s imperative to keep cortisol levels as low as possible if we’re looking to avoid muscle catabolism.
So how can we do this? In the below video, Thomas Delauer does a great job of explaining one strategy for keeping cortisol production at bay.
Essentially, we want to work out at the start of our extended fast and at the end. But not in the middle.
The reason we’re happy to lift weights at the start of the fast is because cortisol is relatively low still, so we can afford to increase it a little via working out without the effects being too devastating.
The reason we can work out at the end of the fast, when cortisol is highest, is because we will be breaking the fast shortly and getting some protein in which will bring cortisol right back down.
Working out in the middle of your extended fast will create this ‘cortisol sandwich’ effect where cortisol was already high because of our earlier workouts and is only going to go higher because we’re still a while away from being able to break out fast!
This probably means we’ll not get anything beneficial out of working out in the middle of our fast and it may actually be detrimental by causing muscle loss.
This is why I only ever workout at the start and ends of my extended fasts. Below I’ll give an example of how I’ve planned workouts around my current 7 day fast to avoid spiking cortisol too high.
Avoiding Liver Glycogen Metabolism
We have two primary energy systems: aerobic and anaerobic. We want to do our best to stay in the aerobic energy system (steady state cardio and low-exertion weight training) for the duration of our fast. The aerobic system is able to burn fat as the primary fuel source. When we’re burning fat, we’re not burning through liver glycogen which is the last line of defence before we start tapping into muscle stores.
If we start activating the anaerobic system by doing too strenuous activity, we switch from fat burning mode and start looking for carbohydrates (glycogen stores in the liver) to supply us with energy. If we do this too much, we deplete the liver of glycogen and the body has to start looking for other ways to get glycogen and it’ll do this by breaking down muscle and converting it into glucose.
Now eventually this liver glycogen will get depleted on a really long fast, but we can preserve it for as long as possible by making sure we enter the fast as fat adapted as possible and by staying in the aerobic energy system for the duration of the fast by not going too hard in our workouts.
How To Lift Specifically While Fasting
So we can still lift but need to make sure we’re doing low volume. We don’t want to be exhausted by the end of our workout by any means.
For example if you normally do 12 reps of 80kg on the bench press, try doing just 6-7 reps on 70kg and then see how 80kg feels. Take long rests in between sets.
You’re not looking to set any PRs here. You’re just trying to send a signal from your muscles to your brain to say that they’re still being used. We’re just trying to do the minimum to keep muscle protein synthesis ticking over.
Below I give an example of how I modified my normal workout to a workout I used while on a 7 day fast so you can get a good idea of how you should be designing your own fasting workouts.
Importance Of Electrolytes
If you’re going to work out during your fast, you absolutely need to make sure you’re replenishing the electrolytes you’re losing through urination.
The simplest way of doing this is to mix up 1 teaspoon of salt with 1 teaspoon of potassium chloride into 1 liter of water and shake well. You can add half a teaspoon of magnesium sulphate (food grade epsom salt) to the mix as well if you have some.
Sip on this throughout your workout and throughout the day. If you still feel as though you’re weak and lethargic, you can add a little more of each of the salts, but I’d recommend no more than 2 teaspoons of each (and 1 max of magnesium) per day.
This is called snake juice and it’s absolute gold dust if you’re doing any prolonged water fast. It’ll make a huge difference as far as energy goes, so make sure you’re taking it!
How I Planned My 7 Day Fast To Maintain Max Muscle
I’m currently writing this on day 3 of a 7 day water fast. I decided at the outset I’d be doing cardio twice daily for the duration of the fast. For me this looks like an hour walk in the morning and an hour walk in the evening.
I also decided I’d lift weights on day 1, day 2, and day 7 only. This is to avoid that cortisol sandwich we discussed earlier.
The benefit of working out on the first 2 days is twofold: A) cortisol is relatively low still and B) liver glycogen stores aren’t depleted yet, so we can afford to train relatively hard without risking muscle catabolism yet. On day 7, our liver glycogen will be completely tapped however, so we have to make sure we take it quite easy still.
My workouts essentially consists of the following:
- 3 sets of 35 x 16kg goblet squats
- 3 sets of 20-25 x 16kg single arm bicep curls
- 3 sets of 8-10 x chin ups
- 3 sets of 15 x 20kg single arm shoulder press
- 3 sets of 8-10x dips
I’m still in lockdown here and the gyms are still closed so unfortunately I don’t have much choice for what exercises I can do. I’m improvising with a 6 pack of 1.5 liter water bottles stuffed into my backpack which I squat and curl at home.
If you have access to a gym you’ll probably want to do heavier weights and far less reps than this. That should stimulate the muscles a lot better. The main thing to remember is to avoid huffing and puffing and getting your heart rate up during a set, as this will engage your anaerobic system.
Lifting weights while on an extended fast is really important to maintain muscle protein synthesis in the absence of food. You need to be stimulating your muscles.
You do however need to be somewhat nuanced in how you approach designing your fast, as well as individual workouts, to ensure cortisol stays low and to preserve liver glycogen stores. This should stave off muscle catabolism as long as possible.
Remember to hit the weights, take your electrolytes, and get some cardio in for best fat loss and muscle maintenance results!