A friend and I were talking about exercise today and he complained that if he really ups the intensity of his exercise he ends up gaining weight as his appetite increases a lot. I'm sure this is something others have experienced and thought the explanation and solution I gave him was worth sharing, so for all the gym bunnies out there here it is:
High intensity exercise is physically stressful on the body and when the body feels threatened it can up regulate appetite and store more fat, particularly around the middle, as a protective mechanism.
The other effect is that long bouts (40mins+) of cardiovascular exercise deplete the muscles glycogen levels. The body will then try and refill these stores, which it is most effective at doing immediately after exercise. Therefore if you don't refuel straight away your appetite will up regulate to get you to eat more carbs later on than you would have needed straight after exercise.
This is where sports nutrition comes in: within 30 minutes of finishing a high intensity work out you should have a snack comprised of high GI (glycemic index) low fat carbs such as sweets (yes Haribo can be good for you!), white bread, jam, breakfast cereal, sports recovery drinks, tropical or dried fruit or fruit yoghurt combined with some protein for muscle recovery. As a rough guide for every 60 mins intense cardio exercise you should eat 1 gram of carbohydrates per kg of body weight.
If you refuel properly immediately after exercise you shouldn't then be craving a lot of food later on and your body should recover quicker improving sports performance and encouraging fat loss.