Im thinking about trying the Ketogenic diet because my friend lost a lot of weight on it
I have heard it helps people lose lots of weight, it works by forcing the body to burn fat instead of consuming carbs. Just be careful not to yo-yo. 
Oh can it be dangerous?
Generally not, the most common side effect is constipation which occurs in about 30% of patients. and has a slight increased risk of kidney stones. 
That still doesnt sound fun, but it would be good to lose some weight.  
I think the diet was originally for treating epilepsy patients, because it seems to reduce seizures by half in young people and children. Still good for weight lose though.
Thats amazing that it was able to help people like that.  Science is so cool sometimes
It works because the liver converts fat into fatty acids  and ketones.