Useless to exercise to lose weight, when you choose fast food. Is the quality of the food that it makes the difference on take calories.
In an article in The New York Times, Aaron E. Carroll, explains that to lose 350 kcal is required to run for 30 minutes: actually to achieve the same result would be enough to give up two cans and a half (139 cal per 33 cl) of Coca Cola. Several studies show that physical activity, that every person should practice it provides many health benefits, it really is not effective for weight loss.
The author of the New York Times, citing many studies in the literature, concluded that the food that is much more important to introduce physical activity in weight control.
For example in Italy to reduce daily calories would be enough to reduce the oil a few tablespoons (-200 kcal), eliminating sugar in coffee (20 x 3 = 60 kcal), drink a glass of wine in less (-100 kcal ) and we would have the result that we can get in an hour of jogging, without great effort and without reducing the amount of food that we introduce.
Vice versa if a child brings snacks that have about 550 Kcal / hectogram and drink orange juice or fruit juice with 40-50 kcal / 100 ml, there is no physical activity that takes because any caloric expenditure will be easily neutralized.
To maintain long-limbed, physical activity is important, but much more so is, to learn how to eat and eliminate snacks, sugary drinks and fast food.