Low Carb Diet Defined
Low-carb diets (low carbohydrate) refers to eating programs that restrict carbohydrate consumption.

These kinds of diet programs are normally used in the treatment of obesity, however a number of medical professionals are suggesting the low carb diets (especially very-low-carb diets) may be used as part of cancer treatment. 

The kinds of diets restrict the consumption of foods that are high in carbohydrates. There are two types of carbohydrates in a normal diet:
- Simple carbohydrates 
- Complex carbohydrates
Simple carbohydrates include sweet items such as sugar, glucose , while complex carbs are found in grains, starch and processed foods like cereals and pasta.

A true low carb diet limits both these kinds of carbs. The amount of carbohydrate allowed varies with depending on the low-carbohydrate diet. Very low carb restriction limits carbs to around 20 grams a day, while a low carb diet often limits carbs to around 50 to 75 grams of carbs a day.
In general a low carb diet is a high fat diet, not as is often assumed, a high protein diet. 
In general restriction of carbs to around 20 grams a day produces a ketogenic state, where the body burns ketones for fuel instead of glucose. This is NOT an unhealthy or dangerous state. In fact, many medical researchers suggest that we spent most of our lives in a ketogenic state in our primitive past.

Some diets like Atkins and the Decarb Diets purposely produce ketosis in the initial phases.

Note that the term "low-carbohydrate diet" is normally applied to diets restricting carbohydrates to less than 20% of caloric intake, but can also refer to diets that simply restrict or limit carbohydrates.

Low-carbohydrate diets can be used to prevent (or treat) chronic diseases including: heart disease, metabolic syndrome, high blood pressure and diabetes, epilepsy,[chronic fatigue syndrome , PCOS (polycystic ovarian syndrome) and some auto immune conditions.