Is it healthy for a 16 year old to go on a diet? i am at my normal weight, intending to lose 5kg.

No need to diet: If your weight is normal, there is no reason to lose weight. Some teens feel they are "overweight" even with a normal weight. If you have questions about your body shape or size or have started restricting your foods or overeating, it is important to see your doctor. You might be at risk for an eating disorder which can have serious complications.