If you decided to keep a diet, you should remember that some cultures and religions have restrictions concerning what foods are acceptable in a diet. For example, only Kosher foods are permitted by Judaism, and Halal/Haram foods by Islam.
A particular diet may be chosen to seek weight gain, weight loss, sports training, cardio-vascular health, avoidance of cancers, food allergies and for other reasons. Changing a subject’s dietary intake, or “going on a diet”, can change the energy balance and increase or decrease the amount of fat stored by the body. Some foods are specifically recommended, or even altered, for conformity to the requirements of a particular diet. These diets are often recommended in conjunction with exercise.