Exercising more doesn't necessarily mean you can eat more
Running a few times a week will mean your body is burning more calories, and you may feel hungrier than you usually do. However, it's easy to overestimate how much more you can really eat - and if weight loss is part of the reason for your running, it's easy to wipe out your deficit entirely with a couple of extra snacks! Try to keep your diet balanced and filling to combat any post-running hunger pangs: Up your energy levels with carbohydrate-rich foods like bread, cereals, rice, pasta and potatoes (wholegrain is best for your heart) and chuck in the essential fats you get from things like oily fish, nuts and seeds. Fish and nuts are also good sources of protein, which is essential for repairing muscles after a heavy workout.
When you exercise you can lose up to a litre of fluid in an hour - so keep yourself well-watered! Make sure you're drinking plenty of fluids during the day - around 2 litres for men and 1.6 litres for women. This will make sure you're hydrated when you start running. Aim to have 400-600 ml water two to three hours before a running session, then 200-250ml 10 to 15 minutes before you start. And if the session is more than 90 minutes, gulp down 200-250ml during your exercise. You could also consider drinking fluid that includes some carbohydrate and electrolytes during your run if it's longer than an hour and a half. Isotonic sports drinks have 5-7% carbohydrate, but you can also make your own - mix 200ml concentrated orange squash (not sugar-free) with a litre of water and a pinch of salt.
Don't exercise on a full stomach (or an empty one)
For short morning runs, you could get away with going on an empty stomach - especially if you've enjoyed a carbohydrate-heavy meal the night before. For a longer run, starting fully fuelled means you have a better chance of completing your challenge to the best of your ability, improving your fitness as part of your training. But eating a big meal too close to a long workout isn't ideal, either. If your digestive system is working hard on the huge bowl of pasta you hurriedly inhaled before lacing up, your muscles won't be getting the supply of nutrients they need. So avoid a big feed within two hours of your exercise - ideally you'd have it 3-4 hours before, but we know how busy you are. A light snack just before your run, like a banana and yogurt or cereal with low fat milk, is fine.