Q: Does your body burn more fat if you do moderate cardio on an empty stomach before breakfast or is it better to eat first?

A: No, I recommend having a light meal before morning cardio. Even something as simple as a scoop of whey protein powder dissolved in water would be a lot better than nothing. Breakfast is called that for a reason -- you're breaking a 10+ hour fast! If you don't eat for a long time, your body has a predisposition for burning muscle instead of fat and doing cardio before eating would certainly encourage that process further.

That advice goes doubly for weightlifting -- please find a few minutes to sit down and have a good breakfast before lifting weights in the morning. And eat again after the weightlifting session before getting on with your day.

There are trainers out there who will advise doing cardio on empty stomach in the morning and then eating. Personally I do not see why it's any more effective than doing cardio after having eaten -- the total amounts of calories you take in and burn off is the same in both cases. But in one case, your body clearly is more predisposed to burning muscle for energy than in the other case.

The one case when exercising on an empty stomach may make sense is for people who simply get sick if they exercise soon after having eaten but don't have time in the morning to wait 30-45 minutes for the food to settle down. If you are like that I guess you will need to choose your priorities. But in general I recommend always eating in the morning before any physical activity.