One needs to regularly go for gym in order to gain weight and avoid the chances of diabetes, heart disease and other metabolic syndromes. Most of the people after losing a considerable amount of weight stop working out, which is not advisable.
From timesofindia.indiatimes.com:
This study furthers research completed earlier this year, in which MU researchers found that participation in aerobic exercise while regaining weight counters many of the risk factors associated with chronic diseases. These studies are some of the first to consider the effects of exercise on people’s health who regain weight they recently lost.
You need to keep exercising; a little weight gain is good to be protective against serious medical conditions. There will be a little gain in your weight and then maintaining is the most important.