Hello,
I am 21 years old boy. I have a height of 5'5 and I weigh about 45kgs. I am underweight and desperately want to increase my weight. Whenever I increase my diet I start gaining weight but as soon as I come back to normal diet schedule, my weight heavily decreases. Professionally I am a college student and dealing with good amout of stress.
Please let me know how to gain weight.
Thanks in advance

Well you could try not going back on your regular diet or just take little bits of it back at a time and eventually your body will get used to that diet and you can live off it but don't gain too much or you will become overweight

What kind of normal diet do you currently have?

What kind of "extended diet" did you try to keep?

At 5'5" and 45 kgs (100 lbs) you are dangerously underweight...regardless, let's try some things...

eat constantly. I don't mean eat entire meals all day...but keep something in your bookbag, car, desk, whatever...just keep on snacking. By snacking, don't eat junk food...eat things that are high in "good fat" such as:

Nuts (these are great small snacks that you can keep anywhere)
Legumes
Meat
Chicken
Turkey
Olive oil
Avocados (GREAT for gaining weight healthily)
Pasta

Also maintain a relatively moderate exercise routine... as you gain muscle, you'll gain more weight as muscle has more density than fat does.

At your age, height, and build, you're burning about 2200 calories a day... so try to consume more than that during the day and you should be gaining weight slowly.

:confused: why do you want to gain weight. If you have a lot of trouble gaining weight it might be because you have a high metabolism. My dad has the same problem. If you truly need to gain weight then having a lot of stress will help. You should also try eating a lot more during the day.

... are you suggesting that he gets MORE stressed out.. I mean... what kind of advice are you giving out here..

I agree with the following: eat more.
But.. don't eat junk food, that won't work. Eat real meals. (Fast food can work but will not gain you muscle and is bad for your heart)

Buy the bags of fruits and nuts mixes that you can carry with you.
Drink milkshakes and eat ice cream (you have the calcium benefit)
Wendy's is a great fast food alternative (baked potatoes, chili, and their burgers are real beef)

I am not an expert but I do have to try to keep weight on my mom who has cancer

Rice all the way