Fasted Cardio Blog Post


Fasted cardio is exactly what the name suggests – performing a form of aerobic exercise in a fasted state. 

Dietary interventions such as fasted cardio are often introduced with the idea of speeding up fat loss and fast tracking our goals. Does purposefully not eating before a workout, despite being hungry have any proven benefits? Let’s take a look at the science behind it. 

Some theories suggest that consistent exercising, while in a fasted state results in bodily adaptations which support fat oxidation (the breaking down of fat cells)1. 

In a study published by the Journal of The International Society of Sports Nutrition, the changes in fat mass versus fat free mass was investigated using a four-week investigation of fasted versus fed state participants. Twenty female participants who performed cardio on a regular basis were provided with customised dietary plans (caloric deficit) and split into two groups1. The first performed exercise after an overnight fast while the other consumed a meal prior to exercise. Training consisted of 1 hour of cardio 3 days a week. Protein intake was set at 1.8g/kg to minimise loss in lean body mass1. Total energy intake remained the same between the two groups throughout the study. The results between the 2 groups were as follows:1

  • No differences in the loss of fat-mass
  • No differences in the loss of lean-mass
  • No differences in percentage body fat
  • No differences in waist circumference 

Basically, no difference occurred whether one consumed food prior to working out or not. 

Our bodies continually adapt and change what is used as a source of fuel. According to the study’s author, Brad Schoenfeld, “There is evidence that a greater utilization of fat for fuel during a given time period is compensated by a greater carbohydrate utilization later in the day. Hence, fat burning must be considered over the course of days not on an hour-to-hour basis”.  

Early morning fasted training can be convenient and certain people prefer it. It may be more suited to your lifestyle to eat after that early morning session however, purposefully skipping a meal before exercising despite being excessively hungry won’t result in any extra fat loss or beneficial outcome. 

What we can take home from the study done by Schoenfeld is that whether we choose to work out in a fasted state or not, it doesn’t really matter. What does matter is what is best suited to your individual preferences and lifestyle.

If you prefer working out after having eaten here are some tips and options to choose from:

  • A mixture of carbohydrates and protein works best about an hour or two before your workout. You’ll give your body time to partially digest some of the food.
  • It is better to include more fats post-workout as proteins and carbohydrates are easier to digest. 
  • 20-30g of protein pre-workout is ideal
  • Smoothies work well as they’re easy to digest and you can adjust the flavours according to what you are feeling like 
  • Other easy options include:
    • Oats with egg whites and maple syrup
    • Greek yoghurt and fruit
    • Egg on toast
    • High protein baked goods such as banana loaves / pancakes 

1: Schoenfeld B, Aragon A, Wilborn C et al. (2014). ‘Body composition changes associated with fasted versus non-fasted aerobic exercise’. Journal of the International society of sports nutrition. 11(54).  

Written by: Nicole Keeling – Registered Dietitian, @cape.townfoods


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