What should i need to eat to gain weight?

High Protein complex: Carbs and healthy fat (fish and plant based fat) is what i would recommend. If you want to put on "healthy" weight, you need to build more muscle. So protein supplements with added 10 grams of sugar and some fruit right after work-outs will help build muscle. I suggest getting your metabolic rate checked and based on that, go on a high calorie zone type diet which is healthy and high protein.