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Then comes the part LOL is a popular and well known brand, so doing something even remotely linked to it will drag an audience. Remember how the World war Z movie ignored the books but paid licencing fee for the title (and the associated _brand recognition)
As usual, weight is driven by Calorie in - Calorie out. If it’s positive you gain weight, if it’s negative you loose weigt.
Your brother is a tall, young male, all of that would point toward a relatively high calorie out also without knowing him in details it’s hard to evaluate. There is always that person taking desert twice when out, but skipping lunch on regular day while doing a lot of sport.