Yes, underweight people should fast. Instead, fasting will be extremely beneficial for you to gain weight in a healthy manner.

 

There is a misconception that more food means more health, which is not true. Food and nutrition are not synonymous. One is not nourished based on the amount of food ingested but in proportion to how much food one digests & assimilates. It is not what you eat but what you digest that matters.

 

Emaciation is not caused due to lack of food but due to reduced health. What you need is not more food but a perfectly functioning, well-detoxified system to be able to digest and absorb the food. Fasting will help improve digestion & food absorption capabilities and help gain weight in a healthy manner.