This chapter gives an overview on nutritional disorders, which includes protein-energy malnutrition (PEM), obesity, and bulimia. Vitamins are vital organic substances required in limited amounts with key roles in certain metabolic pathways. Fat-soluble vitamins and water-soluble vitamins are two categories of vitamins. Fat-soluble vitamins include A, D, E, and K. Fat-soluble vitamins are stored in the body, but their absorption may be poor in fat malabsorption disorders or in disturbances of digestive functions. Water-soluble vitamins include all other vitamins such as vitamins of the B complex group [thiamine (vitamin B1), riboflavin (Vitamin B2), niacin (vitamin B3), pyridoxine (vitamin B6), and vitamin B12] and vitamin C. PEM or protein-calorie malnutrition refers to a group of malnutrition where there is inadequate calorie or protein intake. PEM includes marasmus, kwashiorkor and intermediate states of marasmus–kwashiorkor. Obesity is defined as an accumulation of excess body fat (adipose tissue) that is of sufficient magnitude to impair health. Bulimia is an eating disorder in which the patient binges on food and then induces vomiting. The average age of onset is at 20 years of age.