Nutrition. Muscle mass. Heart problems.

I'm 15 years old 6 ft 1 in (185 cm) and 200 lbs (90 kg) which translates into being 20 lbs overweight.I have read somewhere that exersising while being overweight increases your stamina by working out the heart the same way weight training does is it true or I'm just damaging my heart? If I don't damage my heart in my current condition thought I will lose the weight later(when I'm an adult). If it is a health issue now I'll ignore everything else and lose weight immediatly(1 lbs per day tops). Ofc I'll wait till my exams end to start any diet. My activities will also be less as most probably we won't have basketball training. But since I'm on Syros(a greek island) the impact won't be too much since I'll swim regularly 2-3 times a week. But I think I need to regulate my income(on calories). 5 apples a day plus an occasional ice-cream for 2-3 days are good for starters. Nonetheless I'm still growing and I don't want to destroy my health so how long can I keep up with the 5 apples diet and after the disintoxication what should I follow. Are there any limits on water too?
I'm going to brasil and it's not a place to lose weight with the churascarias(all-you can eat barbeques with little fee at least for my family whose income is 3k per month. Losing weight only to gain(every time I go to brasil I come back with 5 lbs more) it back is not a problem for me unless it would cause any side effects.Lastly I have heard that losing weight while not exersing burns muscles too. Should I wait for the trainings to start anew?


So in a nutshel
Losing weight in my situation is a health issue?
How many days can I keep up with a 5 apples per day diet? After it what should I do?
How much water can I take?
Should I wait for me to return from Brasil/start having basketball training to lose weight?

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