Fasted Cardio for Fat Loss?

Written By Hannah Garrett

Many of you have already heard of fasted cardio. It seems like this trend has been gaining a lot of popularity in the last year.

Why is it such big deal right now?

New research came out suggesting that you could burn more fat when you work out on an empty stomach.

Many of us struggle with fat loss and so we are immediately attracted to this claim. We want to try it out right away.

But, is there any truth to it? Is this the best way to burn fat and lose weight?

We are going to explain exactly what is going on in the body when you do fasted workouts, and give you the information you need to decide if it is the right method for you.

Fasted Cardio 101  

The whole idea behind fasted cardio is that your insulin is low in the morning before eating.

In this state, you are more likely to use lipolysis as your energy source instead of glycolysis. Which, in theory, means you would be burning more fat for fuel, versus more carbs.

It may sound like cutting-edge research, but targeting fat-burning through cardio is nothing new.

You can also activate lipolysis through low intensity cardio (ie. walking). Generally, the more intense the cardio, the more your body will rely on carbs, or glucose, to fuel that activity - and not fat. This is just how our bodies work.

You can also target fat-burning cardio by performing your cardio after weightlifting. Since you have already depleted your stores of carbs through your weightlifting session, your body will be forced to use fat.

So in theory you can “target” fat-burning through cardio. So the question is, how effective is fasting?

When you don’t fuel up with carbs pre-workout, you are more likely to use fat stored as fuel. There is research that backs up this claim as well.  

So, what’s the catch?

The big issue with this study is that it does not account for the hormonal differences between men and women. It also only looks at the effects during the workout, not across an entire day - or the long-term effects over time.

Let’s look at the research as it applies to men, in general first.

Then we will explore how women’s bodies react in a completely different way to fasted workouts.

For The Men…

The studies DO show that you will burn more fat during a fasted workout, however, you will burn less fat during the next 24 hours than you usually would. Additionally, your metabolism will tank if you don’t fuel properly after your workout too.

 You are probably thinking, “What if I work out fasted, and then eat immediately after?”

In general, this would solve the metabolic deterioration. However -

The studies also show that the fasted exercise group were HUNGRIER throughout the day. They were more likely to snack more. This could create a situation where you cancel out the fat you burned by increasing the calories you consume aka. Net energy balance will still be positive (more energy consumed than energy released).

BUT - if you can ignore the increase in hunger cues and stick to a caloric deficit, you will, indeed, lose fat.  

The kicker is – you would have gotten THE SAME EXACT RESULTS if you worked out in a fed state and maintained the same caloric deficit.

This has been proven with multiple studies. 

Additionally, not eating prior to your workout may affect your performance. If you are feeling hungry or weak during your workouts, you would probably perform better if you had a snack before. If you fuel your workouts, you can push yourself harder, and theoretically burn more calories.

So for males, the conclusion is, for most men, do what you prefer. Or rather, do what gives you the most energy for your workout. Overall, what matters most is your caloric intake (how much you eat in a day) vs. your caloric output (how much you move your body in a day).

Just make sure you at least get a meal in after your workout, so your body’s metabolism reboots.

 

For The Ladies….

Our bodies work differently. Our hormones are more sensitive low energy availability than men, and therefore we need to look at a few more factors.  

It has been proven that women do better when they work out in a fed state.

This is because during exercise, we are putting a stress on our body. Intermittent fasting alone, is also a stress on our body.

As women, we utilize more kisspeptin than men. Kisspeptin is a neopeptide that helps us regulate glucose, regulate appetite, and manage body composition. Fasting alone decreases the production of kisspeptin, which disrupts our hormones. Adding exercise into the equation makes the imbalance even worse. Your cortisol levels rise, and your estrogen and progesterone levels are disrupted.

It can cause insulin resistance, muscle loss, fatigue, and thyroid disfunction. All of these can lead to weight gain and an increase in belly fat, especially since our thyroid is what manages our metabolism.

Additionally, if women train in a fasted state, they are more likely to have to breakdown existing muscle in the body to fuel that workout since all the reserve fat & carb stores are being used for critical reproductive functions.

Too much cortisol and it seems our body hunkers down into survival mode, reducing energy output (metabolism) and breaking down existing muscle for fuel.  

This is a drastic difference from when we explored fasting for men. Men’s bodies learn to use fat as fuel when they are low on glucose. Women pull nutrients from their muscle instead.

This is a nightmare for our body composition.

I know it doesn’t seem fair – but just think about what our bodies are intended for. Our bodies are primed to hold another BEING inside of us – and providing enough nutrients so that baby is healthy. Because of this, our bodies hold on to fat and carbs more than men’s bodies do.

Even if you have seen results from fasted workouts – it is scientifically proven that it is not sustainable for women long-term. It will impact your hormones and your body will fight back.

So, what works for the girls?

Eating regularly seems to be the best way to promote recovery and reduce stress on the body. Important note - you can eat regularly and still maintain a slight caloric deficit, so you lose fat.

In general, try to eat 20g of protein and 30g of carbs prior to working out. This seems to be enough to signal to your body that nutrition is readily available.  

One of my favorite pre-workout snacks is throwing a scoop of protein powder in my coffee and snacking on a banana. This fuels my work out without making me feel bloated or uncomfortably full.

 Don’t neglect post-workout fueling either.

Women need 30g of protein within 30 minutes after your workout. We need protein immediately after to get the full effect of muscle protein synthesis (MPS).

Once again – this rule doesn’t apply to men.

Men don’t need to refuel for 3-18 hours after their workout to still reap the full benefits of MPS.  

Make sure you are also paying attention to the quality and macros of the food you are eating. Get 8 hours of sleep and exercise a few times a week. These are all other factors that impact hormone regulation.

 
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