Whether or not you’ll be burning more fat than carbohydrates or proteins will be dependent on your diet and also the primary energy system, and thereby the energy substrates, that your body is putting into use during the workout. With everything else being equal (i.e. you’re not starving yourself and your calorie intake is similar to your calorie expenditure), your body will be mostly burning fat for energy throughout the day when you’re not engaging in physical activities. When you first start to run or jog, your body will be switching from burning fat to carbohydrates. Another switch will occur when you’re working out at a submaximal level (i.e. 40-60% of your VO2Max). When you’re at a near maximal level, there will be another switch and again your body will prefer burning carbohydrates (this is why if you increase your VO2Max by cardiovascular training, you will be burning more fat as you will be able to stay longer in the fat-burning zone). It is not until your exercise bouts start to exceed 90 minutes or so that your body starts burning protein for energy.

I hope this helps!

-Alvin