Compared to an adult of appropriate weight, an underweight adult will have what issues?

Compared to an adult of appropriate weight, an underweight adult will have a higher chance of suffering chronic fatigue. 
An underweight person is a person whose body weight is considered too low to be healthy. Underweight people have a body mass index of under 18.5 or a weight 15% to 20% below that normal for their age and height group. Being underweight may be due to genetics, metabolism, drug use, lack of food, eating disorder, or illness. 

No they’ve not done that