Fasted Cardio For Faster Fat Loss - Fact or Fiction?

Fasted Cardio! I have heard many a personal trainer swear by this as a method of accelerating and maximising fat loss during periods of caloric deficit. In theory, when training after an overnight fast, low glycogen and insulin levels cause the body to shift away from using carbohydrates as energy, allowing greater mobilisation of stored fat for fuel.

Despite having a sound theoretical basis, there is little evidence investigating the loss of fat, over time, in a fasted compared with a 'fed' state, particularly during periods of caloric deficit. It was against this background that Brad Schoenfeld et al. (2014) conducted their research.

The Method (in a Nutshell):

The researchers recruited 20 young, healthy and non-obese females. Thereafter, they assigned 10 to a FASTED group, that performed exercise after an overnight fast, and 10 to a FED group, that exercised after consuming a meal. Participants performed:

• 1 hours steady-state cardio, 3 times a week

They were also provided with customised dietary plans to ensure that they were within a caloric deficit (500 calorie), required to log calories daily via MyFitnessPal and were provided with nutritional guidance to ensure they adhered to the protocol.

The Results:

If we break down the above table, we see a reduction in weight for both the FASTED and FED group, along with a drop in body fat %, waist circumference, and fat mass (kg). However, there were no significant differences in the rate of fat loss between the groups.

Key Take-Aways:

For the time-being, I would say that this novel study has 'busted' the claim that training fasted will accelerate the loss of fat during your 'summer shred' (at least for the general, healthy and non-obese population).

However, I would be highly curious to see the results of the study replicated with a larger sample size, to add further statistical power to the results, as well as for future research to broaden and build upon the question of whether fasted training produces accelerated results in physique athletes in the lead up to competition.

Until that study comes along, we can generally assume that the Average Joe and Jane are free to perform their cardio, whenever they please without fear of 'hindering' their fat loss results.

Reference:

B.J.Schoenfeld, et. al (2014) Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nut, 11(1); 54.