Ok size does matter. Portion size that is. Many runners fall into the trap of thinking they are burning more calories than they actually are and therefore increasing their food intake by too much. Some people who run wonder why they are not losing weight or lose weight for a while and then plateau. It can be a Catch 22 situation, you run and then get hungry so you eat more. Many people underestimate the calorific value of meals and snacks so the balance of what we consume and what we burn is out. To lose weight there needs to be a calorie deficit.