A carbohydrate at its most simple level is a compound made solely of carbon, giving the 'carbo', and hydrogen and oxygen, giving the 'hydrate'.
They come in two varieties depending on the size of their molecule; polysaccharides (which are commonly referred to as complex carbohydrates) and monosaccharides, (which are commonly known as simple carbohydrates).
They are produced by plants that carry out photosynthesis, and so are laid down in starch, sugar and gum.
They are the main source of energy in all animals.
Carbohydrates are contained in many different foods, although primarily in those that are white, such as pasta, rice, bread, and potato; foods that provide the staple diets of many people worldwide.
They are also found in smaller quantities in things like cereal, fruit, popcorn, chocolate, and a whole lot more.
This major food group acts as the fuel that keeps animals going; to move, think, and even to digest more food.
The other reason why we need them is that they are rich in vitamins and minerals that the body can't function without, so it is crucial that we eat them.
The low carbohydrate diet devised by Dr Atkins works on the principle that by limiting the supply of carbohydrates to the body, you can still operate without a problem, only your body uses fat to create energy instead of using carbs.
This works because you eat fat instead of carbohydrates (to stop your craving for carbs) and because this fat is burnt immediately and not absorbed, it does not make you fatter, and in fact reduces your overall body mass in fat.
In short; eating more fat means you end up with less fat.
All the hype about the diet is caused by the unanswered question of whether it causes any problems to your body.
The only obvious problem is that you lose out on some vitamins, but this can be easily fixed by taking vitamin supplements.
Beyond this, there are only theories, but no evidence, that suggest that the diet has any bad or truly negative effects.