In nutrition, the diet is the sum of the food consumed by an organism. Proper nutrition for a human requires vitamins, minerals, proteins, and fuel in the form of carbohydrates and fats. Imbalances between the consumed fuels and expended energy results in either starvation or excessive reserves of adipose tissue, or body fat. Poor intake of various vitamins and minerals can lead to diseases like scurvy or iodine deficiency.
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 the 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. Foods intended to help produce weight loss are frequently labeled "diet foods".
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 the islam, in the diet of believers. In addition, different countries from region to region, have different characteristics. For instance, Americans eat more red meat than people in most other countries, and Japanese eat more fish and rice. Rice and beans are typical parts of a diet in Latin-American countries, while lentils and pita bread are typical in the middle east.
Nutrition is a science which studies the relationship between diet and states of health and disease. Dieticians are Health professionals who are specialized in this area of expertise. They are also the only highly trained health professionals able to provide safe, evidence-based and accurate dietary advice and interventions.
Between the extremes of optimal health and death from starvation or malnutrition, there is an array of disease states that can be caused or alleviated by changes in diet. Deficiencies, excesses and imbalances in diet can produce negative impacts on health, which may lead to diseases such as scurvy, obesity or osteoporosis, as well as psychological and behavioral problems. Moreover, excessive ingestion of elements that have no apparent role in health, (e.g. lead, mercury, PCBs, dioxins), may incur toxic and potentially lethal effects, depending on the dose. The science of nutrition attempts to understand how and why specific dietary aspects influence health.