I watched a fascinating BBC program last week on the Atkins diet. Several scientific experiments were conducted to test Dr. Atkins' claims of how his diet worked. This was the largest medium term trial ever conducted on diet types (300 people, 5 types over six months). The experiments disproved the claims. However, individuals in the experiment on the Atkins diet did loose more weight than both the control group or those on other types of diets. The program investigated this further, with findings summarized as follows:

"At last the mystery of how the Atkins diet works may have been solved. It might have nothing to do with calories being lost. Probably nothing to do with ketosis. And apparently nothing to do with burning more calories. Neither does it seem to be due to gorging on fats. The secret to the diets success may be down to something completely different. Protein makes you feel full. Increasing the amount of protein in the diet may control appetite and make people eat less than they would normally."

http://www.bbc.co.uk/science/horizon/2004/atkins.shtml