Therapeutic nutrition is the therapeutic adaptation of the normal diet. Diet therapy is the use of food  as an agent in effecting recovery from illness. It is concerned with the nutrition of all patients, those receiving normal diets as well as those for whom modified diets have been prescribed. Modified diets are the principle therapeutic agents in some metabolic diseases such as diabetes mellitus.
In some other forms of diseases, diet therapy serves as a preventive measure as well as therapeutic aid. Example: Fat control diet may be beneficial to those individuals who are likely to develop coronary disease.
For therapeutic purpose, the normal diet may be modified for the following:
1. To provide change in consistency as in a 'fluid' or 'soft' diet.
2. To include grater or less amounts of one or more nutrients-high protein, low fat, low sodium, high carbohydrate.
3. To increase or decrease bulk as in high and low fiber diets.
4. To provide food, bland in flavour as in peptic ulcer.
5. To exclude specific foods as in allergic conditions.
6. To modify the intervals of feeding.

The purpose of diet therapy are:
1. To maintain good nutritional status.
2. To correct deficiency which may have occurred.
3. To afford rest to the whole body or to certain organs which may be affected
4. To adjust the food intake to the body weight whenever necessary.

In order to play the part of dietitian, they should have the knowledge of:
1. The underlying disease condition which require a change in the diet.
2. The possible duration of the disease.
3. The dietary factors which must be altered to overcome these conditions.
4. The patients tolerance for food by mouth.

The planning of the therapeutic diets implies the ability to adapt the principle of normal nutrition the specific disease condition as well as for economy and palatability. A correctly planned diet is successful only if it is eaten. Therefore, care should be taken for the service of not only nutritious, but appealing and palatable food to the patient. The planning of meals also necessitates consideration, religions and cultural patterns, availability and cost of food and suitable methods of preparation.

TYPES OF DIET
1. Soft diet: This diet represents the dietary step between the liquid diet and the normal diet. It may be used in (i) acute infections (ii) some gastro-intestinal disturbances, etc. The diet is soft in consistency, easy to chew, made up of easily digestible food and contains no harsh fiber, no rich or highly flavoured food. It is nutritionally adequate when planned on the basis of the normal diet.
Foods included are: milk, eggs, potato, finely chopped or strained vegetables, bananas, pappaya, fruits without skin, broken cereals, porridges, well cooked rice, puddings etc.

2. Liquid diet: Liquid diets are used in fever, soon after an operation or whenever the patient is unable to tolerate solid foods. They are of two types:
(i) Clear fluid diet  (ii) Full-fluid diet.

Methods of feeding:
Food is given through mouth, when the patient can eat, digest and absorb sufficient food to meet his nutrient-requirements.
But in severe illness, it may be necessary to give food either by (i) Intravenous feeding and (ii) Tube feeding.