I have been very thin my whole life, well, it started when I was about 10. The doctor told me that I have a fast metabolism, which means my body breaks down food quickly and only stores a very little amount as fat.
So basically, if I were to intake a lot of calories, I still would not gain weight. People simply tell me "Eat McDonald's everyday"!. trust me, I've tried that but with no luck.
Is there ANY possible way to gain weight by slowing down my metabolism? What certain foods should I be eating? Proteins, carbs, calories?

You don't say how old you are now --16? 36? 55? If you're still in your teens or even early 20s, I'd not be too concerned about packing on the pounds, but would rather join a gym and increase my muscle mass --not to look like Hulk Hogan, but to have smooth, streamlined arm and legs and be very fit.

That means too that you will have to zero in on your nutrition and do some research on the best foods to eat to be healthy.

You have the best of all worlds -- being healthy, slim, and able to wear nearly anything (big prints, knit tops with lots of layers, horizontal stripes, etc.) and look good.

I'm sorry, I forgot...
I'm 17, turning 18 in about a month. And your advice about hitting the gym has not worked for me. I've tried it already, and instead of gaining muscle, I ended up losing so much weight :( it was the complete opposite of what I wanted. So exercising PERIOD is out of the picture.
Besides, I'm looking to gain WEIGHT, not muscle. And I need to do that by slowing down my metabolism... but how?

Thank for your answer though!

If you were exercising and losing weight, the exercise plan wasn't being done right.

Have you seen a doctor or nutritionist about the metabolism problem? Has a doctor checked your thyroid functioning?

Also, try grazing -- eating many small meals throughout the day.

I'm not looking to gain muscle though... I want to put on a little fat first, and then maybe begin exercising to build muscle.

kittygirl5 - I'm in the same boat as you it would seem. I'm 17, 5ft 7 and weigh just about 150 lbs. I eat like there is no tomorrow and yet still don't put on any weigh. I've been told to try protein shakes... I'll let you know how I get on with that and then maybe you should give it a try.