Disease is very difficult to define, because many diseases are multifunctional in both their symptoms and how someone comes about developing such diseases. Diseases that are fatal or disfiguring are easily defined as disease, but diseases that in between the physical and psychological are not quite as easy. Obesity is a disease because it not only falls under the criteria of disease, but is comparable to many disordered that can considered diseases.
Physical disease is when the body is physically unable to function. An example of a physical disease would be Cerebral Palsy. This is a disease that is thought to be the result of trauma to a child's brain before, during or after birth. It can affect a child in varying degrees of physical disability. There are several types of Cerebral Palsy which affect different parts of the body; Hemiplegia affects either the left or right side of the body, Diplegia affects both legs, and Quadriplegia affects both arms and legs equally.
There is nothing wrong with the sufferer's mind and it does not affect the life expectancy of the person (Wikipedia Cerebral Palsy).
Mental disease is when the mind has been distorted in some way to produce a behavior which is considered as "abnormal". Anorexia nervosas is a good example of this, as the sufferer has a distorted image of themselves and believes that they are fat. They restrict their food intake and up their exercise regime to the point of extreme ill health. There could be many reasons causing someone to be anorexic. Many believe it is the feeling that the sufferer is not in control of their lives, and food and exercise is something they can control. Others believe that the sufferer is struggling to cope with becoming an adult. Whichever the reason behind such behavior,