Much of calories you consumed come from glycogen first,
then from fat. Long run, defined as at least 10 miles
or 90 minutes, can deplete glycogen and tap your fat.

Last year, I consumed calories eeuiavlent to 30
pounds of fat. But my weight remain the same
because I increase food intake too. I don't have a weight problem.

By the way, if you weigth does not change, it does not mean exercise has no eeftec. Maybe your fat amound
decrease and you increasd e your muscle. Also weight
loss is only one goal of exercise