Wow! Good for you on your run!!! Maybe you need to allow yourself to have some of the activity calories if you don't already. I would imagine that a half marathon would leave you with a big deficit. 1547 days ago
Eating food helps--make sure you are eating healthy foods. Your muscles need more nutrition when you use them. Also, it takes calories to burn calories!
AND--stay hydrated. The body can put out the same signal for hunger as thirst, before you feel thirsty. I have read that when you feel thirsty, you are actually at the point of dehydration. So it's important to stay hydrated.