fasted cardio

Posted 2 years ago

Do you need to do fasted cardio?

One of the most commonly asked questions surrounding cardio is whether doing it fasted, first thing in the morning, burns more fat than if you were to do it at any other time in the day.

I won’t even encourage you to google it, because there is an overwhelming number of different opinions out there. Some coaches swear by it without any logical reasoning behind it, whereas others are completely against it and will always encourage you to eat before cardio. But who’s right? Well, the purpose of this article is to discuss fasted cardio and how it relates to fat loss, describe why some people may recommend it, and also reflect on my own personal experience.

For the purpose of this article, we are going to refer to a fasted state as having eaten the night before but having not eaten anything in the morning.

Aim when dieting

Before we get into debating the pros and cons of fasted cardio, we need to establish what the aim of cardio is when we are dieting. As you may have already guessed, the goal is to create a negative energy balance, so that fat loss can occur whilst we hold on to as much muscle mass as we can.

To better understand what I mean by energy balance, imagine a seesaw, where on one side you have food which is your “energy in”, and on the other side you have all the activity you take part in during the day (e.g., steps, cardio, training, NEAT), which is your “energy out”. In simple terms, to lose fat we need to be in a negative energy balance, where we’re expending more energy than we’re taking in. When our body finds itself in a negative energy balanced state, it will use our use our fat stores to provide the body the energy difference that we have created across the day/weeks, and thus we have ‘fat burning’ (lipolysis).

Creating a negative energy balance will, for the most part, take days and sometimes weeks to accumulate. This is why if you are adherent to your diet Mon-Fri and go off the rails Sat/Sun you will not lose much body fat. Therefore, I would suggest that if you are dieting, to be consistent and also patient with the process. It might take 3-4 weeks before you notice any difference.

Anyway, the point I’m trying to make here is that cardio in and of itself, is just one of the many tools we use to create that negative energy balance. Whether you like it or not, cardio will always be part of any dieting phase. This may come in the form low intensity steady state (LISS) such as steps or high intensity interval training (HIIT) such as sprints on the spin bike.

When we’re dieting though, we want to go with what is most efficient and creates the best returns for our goals, which is why the notion of fasted cardio became so popular. Because of course, if I’m doing cardio to create a negative energy balance, but doing that same cardio creates more of an energy deficit if I do it fasted, why would I not?!

Pros of fasted cardio

If you are dieting for a show or a shoot, it will be quite common for you to be using lipolytics – supplements that aid fat loss. Those supplements can include but are not limited to: yohombine HCL, clenbuterol and growth hormone.

Yohombine and clenbuterol are explained in great details in other parts of the site but they both have a stimulatory effect on the CNS, causing a rapid increase in adrenaline, which can bind to the beta receptor (good receptor) in fat cells, eliciting fat loss. Adrenaline can also bind to the alpha receptor (bad receptor) which doesn’t allow this to occur, but Yohimbine blocks this receptor, meaning we get the best of both worlds.

However, when taking Yohimbine we need to be mindful of the fact that the hormone insulin, which is produced by the body once we have eaten food, cancels its effects. Thus, to get the benefit from Yohimbine, it must be taken as far away from food as possible, and the easiest time to do so would be first thing in the morning.

The large adrenaline production by clen will not require you to be in a fasted state to elicit fat loss, but often athletes will combine both clenbuterol and yohimbine. The more adrenaline in your system, alongside the ‘bad receptor’ being blocked means more fat loss can occur, and since you need to be in a fasted state then many just take advantage of it and get their cardio done in this state.

Similar to Yohimbine, the evidence on Growth hormone (GH) suggests that its lipolytic effects are improved in a fasted state – that is, it upregulates fat loss in a fasted state, with one study finding that it ‘doubled the rate of lipolysis’ [1]. In Laymen’s terms, it speeds up fat loss without you having to manipulate energy balance. This is of course something that we would take advantage of. However, this certain study showed participants fasted for 2 days prior to testing. We know that this is unrealistic for bodybuilding as we would inevitably lose muscle mass. However, it still is applicable because we will tend to inject more than the body will produce naturally. Therefore, the correlation between increased levels of GH in a fasted state increasing fat loss, still holds strong.

With this in mind, another thing we need to factor in is the fact that these substances will increase adrenaline production, which we’d preferably avoid later in the day. As such, one of the benefits of doing fasted cardio would be that you have the additional adrenaline boost from these compounds, meaning that you might even work harder during your cardio. Therefore, whilst there’s no specific benefit to doing cardio fasted on its own, it makes sense to put cardio in fasted when you’re taking these substances anyway.

Cons of fasted cardio

Now that we understand why fasted cardio might be preferable and helpful in some instances – if we’re taking lipolytics – let’s look at the situations in which it’s not, which would be if we assume you’re not taking any supplements to help with fat loss.

Thinking back to the paragraph on energy balance, the bottom line is that in order to lose fat, all we need to do is create a negative energy balance. Therefore, if your goal is simply to lose a little fat, you won’t be using any supplements that benefit from you being fasted, and thus you don’t need to do your cardio in a fasted state. It’s also worth considering the fact that you might struggle to perform your cardio at a high intensity if you haven’t got any food in you. In fact, your performance could improve if you’d eaten a meal 90 minutes prior to doing your cardio.

And why does cardio performance matter? Well, thinking back to creating a negative energy balance, it might be that if you do your cardio fasted, you find that you don’t push yourself as hard. As such, your energy output or calorie burn will be lower when compared to a session you might do after having eaten some food. Although the difference might feel insignificant – something like a 50-100kcal difference – if you were to add that up over all your cardio sessions, it quickly adds up to a lot.

Therefore, if you are simply dieting to shed some fat and it isn’t too aggressive, it would make more sense to do cardio whenever it suits your schedule and whenever you are able to perform to your highest possible level.

Personal experience

I’m quite open about my use of performance enhancing drugs, and I do use clenbuterol and growth hormone. Back in 2017, I dieted for a men’s physique show doing fasted cardio (figure 1), then in 2019 cardio in a fed state (figure 2), then in 2020 doing fasted cardio (figure 3). You could say I’ve done it all.

Figure 1                                      Figure 2                                      Figure 3

Now that I’m prepping again in 2021, I’ve chosen to do my cardio fasted. Why? Simply because it works better for me. Yes, I get the benefit of increased fat lipolytics but also, I just like getting up and getting it done. It’s probably my least favourite task of the day and that being said, I like to box those off first.

Although you will see increased fat loss from doing fasted cardio when taking lipolytics, it’s not compulsory or part of the rule book. For example, if doing so means you are losing out on 1-2 hours of sleep, it’s not worth it: always prioritise recovery. If your performance is poor whilst doing it, it’s not worth it. Instead, just do it later on in the day.

In summary, when dieting, look for ways to achieve a negative energy balance and be patient. If you are only undertaking a short dieting phase and looking to lose only a few kilograms, you don’t need to consider doing fasted cardio if it’s not your preference. If you are prepping for a show and using lipolytics it would be favourable to do your cardio in a fasted state to gain the benefits of increased fat loss.