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Should I workout on an empty stomach?

February 16, 2020

it has long been held that working out on an empty stomach, or fasted cardio, is one of the best ways to lose weight and lose body fat quickly. There are a number of reasons why this rumour started circulating, but is there any truth to this? and will it help you shed those Kg's faster than if you worked out after breakfast. 

 

Let's take a look at what the evidence says and if doing fasted cardio really lives up to the weight loss hype? 

 

What is fasted cardio?

When is the best time to workout on an empty stomach?

When it is not ok to workout on an empty stomach?

What are the best types of workouts to do as fasted cardio?

Can you enter the "Fat burning" zone when not doing fasted cardio?

How long should you eat before doing a workout?

What should you eat before a workout?

So, should you do fasted cardio?

 

What is fasted cardio?

If you workout in the morning, chances are that you workout before breakfast and it would have been roughly 10 - 12 hours at least since you last ate. Although you don't have to wait that long, as fasted cardio is technically when your body has finished processing it's last meal, which can be between 4-6 hours after you last ate. It would be hard for anyone to find a time during the day that it would be a long enough time between meals. When you workout on an empty stomach, your levels of insulin (the hormone that gets produced in the body by the pancreas when you ingest food) will be at it's lowest level, generally below your baseline level. When these levels are low, there is only a relatively small amount of readily available glucose in your bloodstream to be used for energy. Thus, your body must rely on it's stored fat and glycogen in muscle to fuel your movements. Meaning that you enter the "fat burning" zone quicker than you would if you worked out just after you ate. 

 

 

When is the best time to workout on an empty stomach?

The best time to workout on an empty stomach is first thing in the morning as it would have been numerous hours since your last meal, presumable dinner the night before. Although for Night shift workers this could vary as they may come off shift at 6am, go straight to sleep until 1 or 2pm, so then doing cardio when they wake up mid afternoon, before they ate would be fasted cardio for them. 

When your insulin levels are low and you don't have as much glycogen to be able to fuel your workout, it is even more critically important to listen to your body and what type of workout would be best. A high intensity workout on an empty stomach may leave you feeling lightheaded and dizzy whereas a morning walk or bike ride may be ok.

 

When is it not ok to workout on an empty stomach

If you are doing a high intensity workout at the end of an intermittent fast (16 - 18 hours without eating) you will most likely feel tired and sore half way through and may get dizzy and light headed as you will not have enough stored glycogen to get you through the workout. We typically only have enough stored glycogen to get through about 45 minute to an hour workout. 

This can also cause muscle being used up for energy and thus cause muscle loss and wastage. This is something that you do not want as muscle gives you definition, shape and tone. 

 

What are the best types of workouts to do as Fasted Cardio?

The best types of workouts to do after an intermittent fast is a light walk or run. A high intensity workout on an empty stomach may leave you feeling lightheaded and dizzy whereas a morning walk or bike ride may be ok. One where you are exerting yourself to about a 5-6/10 and are slightly puffing but can still hold a conversation with ease. 

 

Can you enter the "fat burning" zone when not doing fasted cardio?

Our bodies generally have enough blood glucose stores to fuel for a 45 - 60 minute continuous workout - as long as there is oxygen entering the body, as you need oxygen to be able to burn fat. So exerting yourself to about a 5-6/10 and are slightly puffing but can still hold a conversation with ease. Thus the most time when you burn fat is when you are exercising at a 50-65% capacity. Going for a power walk or swim for 40 minutes is going to help you to burn more fat than doing a 20 minute HIIT session at 95% capacity.

 

How long should you eat before a workout?

If you are exercising later in the day or afternoon/ night chances are that you would have eaten relatively soon before your workout. My rule of thumb is to not eat at east 1.5 - 2 hours before a high intensity workout. For a slower paced walk or workout where you are not exerting as much energy, it isn't as crucial the timing but I still recommend not eating for at least an hour before going for a walk. This will give your body enough time to have digested the food and you will be able to have a better workout.

 

What should you eat before a workout?

In terms of what should you eat before a workout, a light snack always works well, not a full main meal. Something which isn't too high in fibre as that could make you need to go to the bathroom in the middle of your session or run. A piece of fruit such as an apple, a banana or handful of nuts are always good options. If you are a night owl who prefers to train after work or after dinner. Leave a couple of hours after your meal or split your dinner into 2 so that you aren't as full during your workout and you are sure to be hungry post workout so will leave you something to eat. 

 

So, should you do fasted cardio?

If you exercise in the morning, then chances are that you will be doing fasted cardio as generally people won't have time to wake up, have breakfast then wait 2 hours to train, they would generally train first thing before breakfast. However, if you are training mid morning, afternoon or dinner, it if significantly harder to ensure that you have the 4-6 hour window after eating before training so they will generally be training within an hour or 2 after a meal. 
 
Both have their benefits, and one does not outweigh the other in terms of effectiveness.
 
The best workout is the one you do. Don't waster your time thinking oh i can't do a fasted workout today so i might as not workout, whatever workout you do is better than none!
 

 

 

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