If obesity is disliked by all those who are figure conscious, then the extremely thin people equally dislike being thin. Such people wish to put on weight. It is a fact that anything that is either in excess or deficient cause disease if left uncontrolled. While obesity causes diseases of vital organs of the body which are degenerative & crippling in origin, emaciation also causes infectious & febrile diseases. That is why someone rightly said, "life is full of extremes & contrast". Two of mankind's most pressing problems seem to be how to keep half the population from starving & the other half from being overweight. Thinness or emaciation is the condition when there is weight loss, either gradually or suddenly. Active illnesses, as in any fever like typhoid, measles make one thinner. In such cases, once complete cure of the disease takes place and if there is return to normal eating habits & activities, the lost weight is usually regained.

There are three types of people who are extremely thin.

Those who eat well & stay thin.
Those who cannot digest whatever they eat and inspite of a good living because of illness or deficiencies & remain thin.
Those who are undernourished & over worked.