Instructors often talk about mobilising fat as energy as opposed to glycogen (carbs) during training sessions as way to help you achieve a leaner body. This is more commonly known as fasted cardio. There are multiple ways you can do fasted cardio including maintaining a lower blood sugar level in general, ingesting omega 3 fish oil or training at a very high intensity using interval training (HIIT).

Before looking at the pros and cons of fasted cardio, it's worthwhile noting that whilst many people do HIIT in a fasted state, this in some ways doesn't suit. HIIT is designed to speed up your metabolic rate and help you keep burning fat for many hours post-workout. So if you're looking to maximise fat burning during a session (which is what you desire from fasted cardio) then the two don't necessarily work in harmony.

If you're keen to give fasted cardio a go, here's what you need to know...

Pros:

1. A study done by Jenna Gillen PHD from The University of Toronto found that fasted cardio will assist in oxidising fat and help with those problematic and stubborn fat yielding areas i.e. the inner thigh and lower abdominal area. So if this is something you struggle with it may well be worth trialing fasted cardio sessions.

2. It's a really simple one but if you're fasted before training it can help you keep your calorie intake lower that day. If you're on a calorie deficit diet and looking to cut down your food intake then this can be a good way to remove a meal's worth of calories by avoiding pre-training nutrition altogether.

3. John Kiefer, a physicist and nutrition expert says: "When you're fasted in the morning, the hormone cortisol is high and its only job is to break down the appropriate tissue based on what other hormones are around. Insulin is elevated after eating and cortisol will attack muscle. But, if you are fasted, insulin is low and cortisol will then go after body fat reserves."

Cons:

1. In light of increased stress and metal health issues in general, it's important to note that fasted cardio can actually lead to increased anxiety levels. When you rise in the morning your fight or flight hormone cortisol is released - when you fast and/or do exercise it is also released. So, you could actually double or triple your cortisol levels. This is too high for some people leaving them feeling anxious post-workout and potentially all day. Fat loss slows downs dramatically when you're stressed so it's important that you listen to your body.

2. Losing muscle mass is a common side affect of fasted cardio as muscle proteins are more readably available for use as energy. To help combat this, I would recommend taking some supplements pre-session, BCCAs and/or a protein shake. I would also recommend adding some good quality fats like coconut oil so as not to cannibalise muscle proteins. After all, nobody wants to be losing weight in the wrong way.

3. There is also a potential for lower tolerance in cardio sessions in a fasted state especially for someone that's been out of training for a while. Many people suffer with light-headedness or dizziness when trying it for the first time. 

Verdict:

I feel the positives outweigh the negatives and with the right attitude towards fasted cardio training you will likely see some fairly quick results. As with anything fitness or nutrition related you must try and test it on yourself to see how you react. 

Now, read Dan's earlier column about how exercise can positively affect your career