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Fasted Cardio for Fat-loss

There is still some debate as to whether fasted cardio is superior to fed cardio for fat loss (once total calories and protein are matched).

The general premise behind performing cardio after an overnight fast is that it accelerates fat loss more than if you completed the same work in a fed state.

To shed light on the topic, Schoenfeld and colleagues tested body composition changes associated with fasted versus non-fasted aerobic exercise in 20 healthy females who were randomly assigned to either group.

Following four weeks of aerobic exercises during dieting conditions (ie, being in an energy deficit), both groups lost body weight and fat mass. The key finding was that there were no significant between-group differences shown in any outcome measure. Put simply, the fasted group did not lose significantly more body fat compared to the fed group.

If that’s the case, what is behind the idea that fasted cardio could be superior for fat loss?​ For that to be the case, fasted exercise would have to achieve one of the following:

• Affect 24-hr energy expenditure so that the energy/calorie deficit is increased
• Suppress appetite leading to a reduction in calorie intake
• Have a protein-sparing effect delivering higher retention of fat-free mass (and therefore making a higher proportion of the weight-loss to be fat)

None of these conditions have been shown to be true!

Interestingly, a recent study on skipping breakfast before resistance training found a reduction in performance on the bench press and back squat. The male participants were resistance-trained and habitual breakfast eaters, providing solid evidence that fasted resistance-training performance among those who normally have breakfast may be compromised over the short term.

If you prefer, and feel better, training fasted without any comprise on performance, then go for it! But if you feel terrible training fasted and/or are only doing so for the proposed fat loss benefits, reconsider your strategy and include a meal/snack/shake beforehand instead. Fat loss will not differ once total calorie and protein intake remain the same. As always, for fat loss success, consistency and patience is key!

The best way to understand your fat and muscle composition with a DEXA body scan. You could try one protocol (eg, fasted exercise) for three months; and a different protocol for the same amount of time. DEXA scans which ‘book end’ each consistent protocol, as explained in this DEXA information video about frequency, will show the differences. But be careful – your experiment is unlikely to be scientific and control for all variables, especially over sustained periods. You are likely to change diet, workout and meal timings, and exercises. That said, DEXA is the best way of tracking body composition over time.

Kevin Garde
Bodyscan Consultant and Nutritonist

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