In nutrition, the sum of the food consumed by a body is its diet. Proper nutrition for a human requires vitamins, minerals, protein, 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.
Changing the dietary intake or going on a diet can change the energy balance and increase or decrease the body fat of a body.
In politics, a Diet is a formal deliberative assembly. The term is derived from Medieval Latin dietas, and ultimately comes from the Latin dies "day." The word came to be used in this sense because these assemblies met on a daily basis. (see the external link below).
This word, unlike the diet above, is pronounced dee-it (with a long E sound rather than a long I sound), as in the word deity.