[omid (OP)]

Hey guys I am 17 and my wieght is 45Kg.
my question is that why don't I get fat its not that I am too skiny but I want to be a little fat, what should I do? []
Btw I do eat a lot of junk food []

[JnA]

I'm going to go with 'metabolism'.

How tall are you?

Eating junk food isn't that great even for people with high metabolism. Skinny on the outside does not indicate good health or healthy organs. In fact organs (like the heart and liver) can have a layer of fat around them not discernible from the outside, which increases risk.

So how do you put on weight?  The way to do it is to build muscle. For that you need the right foods and the right exercise. Talk to someone who knows about 'hard gainers' and can see you physically.

Good luck.

[omid (OP)]

my Hieght is 165cm and would omid look good growing MUSCLES []

[JnA]

that gives you a BMI of 16.5.  which is considered underweight.

BMI is not a great indicator of health or body type for the individual (it's generally considered a comparative tool), but it's a starting point.

Just watch your intake of types of food. Just because you don't gain visible weight does not mean you can ignore good eating patterns.

[neilep]

I wish I could eat junk food and not get fat !*le sigh*

[BenV]

At 17, there's also a strong chance you're still growing - your body needs the energy resources from your food for growth and development, rather than storing it up.