Is it true that when you go through puberty you lose a lot of weight and you also get taller?

Taller, yes; lighter, no

It is quite common for adolescents to appear to get thinner when they are actually maintaining their weight and getting taller. Actually losing weight is not typical, and losing lots of weight is not normal, unless the person, who may be more concerned with appealing to the opposite sex, is consciously trying to cut down on the calories.

Lots taller lighter hell no

Im also 11 and ive actually grown about a foot since i was 10 ill be 12 in february so you do get lots taller but i weigh 105 pounds still i wouldn't say im overweight just a bit broad but i am appearing to be much thiner and taller