Correction to my previous answer to your question re sun exposure and Vitamin D – in this morning's newspaper. "All you need is 5 minutes of sun exposure a day, three to four times a week, on a skin area the size of your hands or face…..On balance, it's better to minimize the risk of skin cancer (with sunscreen)…..Make sure the sunscreen blocks UVA as well as UVB rays (broad spectrum) and is rated at SPF 30 or higher….use about two tablespoons to cover the entire body….repeat every three to four hours."

Everything that you eat gets turned into simpler compounds before your body can process them. You body will burn sugars first and then fat. The bile from your liver helps to break down fat and from there it is digested and sent out through the body. The foods that we eat are what our body used for "fuel" first and then we use the stored stuff. You actually need the fat in the foods that you eat to keep your body going. The human body is actually like a very complex machine and the food you eat is what the cells use for energy. As long as you don't overeat, or eat exessive amounts of very fatty foods then you are fine. The laps you swim will help, and after exercise like that your metabolism is a bit higher, and you will even metablolize fat at a faster rate. Good luck to you.

Your body has to get more calories than it uses to store the energy, that is how we gain or lose weight. Regardless of whether what you eat is fat calories or complex carbohydrates it is the same thing. If you exercise and burn more than you ate then you do not gain weight. Your idea of burning the calories before you digest them is not the way it works. You can not burn off calories before they leave your digestive track. You do not burn off the new calories while they are in your stomach or intestines. So if you are counting calories and exercising eat healthy and you can control your weight.

I don't think so, for your body to utilize something it has to be processed first. So the food that you just ate is not digested yet so it's not available for use. The food is then going to be broken down into energy for the body to utilize I am not sure how long this process takes but I'm sure you can't do what you described. For the first 30 minutes your just going to be using the quick energy that you body has already prepared with the carbs that you ingested hours earlier.