Distance Running and weight loss

I'm trying to lose 10 pounds and was wondering if it is unhealthy to not eat back the exercise calories. I'm female, 50's and my bmi is 24. If I lose 10 pounds, my bmi would drop to 22.3. I want to be thinner since I love to run 5K to HM competitively, although I am not really fast, just an average runner who does well at local races in my age group. I ran 16 miles at a 10:10 pace yesterday and did not eat back any of the calories. Now I wonder if I should eat back at least some of the calories when I do long run.