Add healthy calories to your diet. Spend a few days tracking what you eat and reading the nutritional panels of all your foods. Then you'll know where you need to add on to your diet. An easy fix is to just add a Boost shake or an Ensure shake between meals. But be careful of your fat intake and your cholesterol. I've been on a weight-gain campaign of my own for several months now (I've gained 5 pounds so far - woo hoo!) but now my cholesterol is too high.