A diet comprises those foods that one lives on from day to day. Generally, humans are either omnivores or vegetarians. Omnivores are people whose diets consist of plant and animal food sources; whereas, vegetarians live on vegetables and fruits only.
The New Webster’s Dictionary of English Language defines diet as; the food and drink normally taken by an individual or a group or a prescribed course of what is to be eaten and what is not. This definition takes into account the fact that what you drink e.g. Milk, water, beer, whisky etc is part of your diet.
There is a saying that, you are what you eat, meaning that your diet can go a long way to predict what you will become in future considering that some diets confers longevity and some kill you fast.