The odd treat won't do any harm and you do need a decent meal in you. If I am staying away then I would go to an Italian restaurant and have pizza or pasta. So I guess none of my options are that great diet-wise, but it's only for a race, not every day. But for racing it is good to have plenty of carbs, and you'll burn over 600 calories doing a 10k ...not that much less than fish and chips. I find that when running I can treat myself too much because I'm running, but at only about 100 calories a mile it doesn't take too many choc bars to undo the good work! So, everything in moderation...