Basically a Ketogenic diet is a diet devoid of any starch or sugar.

Normal metabolism is based predominantly on the burning of simple and complex sugars, along with the proteins and fats we eat.

When the body is starving, it switches from a metabolism to a metabolism based on burning fat and protein. This is a natural survival mechanism that allows people to live on very little calories.

Ketogenic diets trick the body into going into a starvation mode. When there are no starches to be burned, the body will start burning endogenous fat and muscle in order to make the energy it needs, along with the protein and fat that is eaten. The liver also starts making its own sugar to meet the minimum needs of the body (gluconeogenesis). A byproduct of type of metabolism are ketones, hence "Ketogenic" diet.

A purely ketogenic diet is made up of all protein and fat, without any carbohydrates. Realistically one can eat a little cars, say less than 30 grams a day, and still stay ketotic, particularly if the person starts with four or five days of 0 carbs a day.

A side effect of this diet is weight loss. To some this is good, but to somebody who doesn't need to lose weight it may not be good. Unfortunately it is not a good weight loss either - after a long time on this diet you don't look healthy thin, you look more starving thin - because your body thinks you are starving and is burning the stuff it thinks it needs to burn to survive.

The "Atkins" diet is a pure ketogenic diet. The "South Beach" diet is a somewhat less ketogenic diet, but allows some complex and fiber based carbohydrates. Not as deeply ketotic but the same idea.

On any of these diets, one can check if its working by using a urine test strip, usually available in health food stores or pharmacies. The ketone part turns very purple if you're ketotic.
Source(s):
Personal expertise as a physician and former ketotic diet experimenter.


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