If you prefer to do fasted cardio because you cannot stomach food beforehand, this is fine. However, it is unlikely to provide any additional benefit compared to fed cardio.
There is currently no evidence to suggest that fasted (empty stomach) is more beneficial than fed (eating before) cardio.
The theory behind the idea that fasted is superior to fed cardio is that because you are in a fasted state, you will burn more fat for energy compared to fed. What actually matters is fat oxidation over a longer period (24 hours, 7 days etc). In other words, just because you’re burning more stored fat during 30 mins of fasted cardio, doesn’t mean you burn more fat over a longer period. You will perhaps in that short window, but it’s still calories in vs calories out, and it evens out over the course of the day.
A 2018 pilot study actually showed ingestion of protein prior to cardio go increase post-exercise energy expenditure, and saw no significant differences in fat oxidation compared to not eating anything at all.
However, some people simply prefer doing cardio as soon as they wake up, which is fine. If your goal is to get to extreme levels of conditioning and/or maximise muscle retention, we’d recommend having some form of protein before or during in the form of a protein shake or BCAAs. If not, make sure to eat soon after.