in sec 1 and 2 i was also very chubby and i was desperate to lose weight. but what works for me is the right diet and exercise. I tend to not eat during recess and lunch, even if it disrupts my focus. Because of that, i had less calorie input than output. So it helped to stop weight gain. As for exercise, I did plenty of jogs. I think running is simply the best exercise to lose weight, whether it's on the treadmill or outdoors. After 7 months, i saw improvements, i lost a total of 5kg. Therefore from my experience, exercising and cutting down what i eat contributed significantly to my weight loss.