Phase one of the Atkins diet needs to last a minimum of 2 weeks, as stated by Atkins. Phase one can be longer if the weight needs to be lost in a shorter amount of time or if a person is morbidly obese.
Phase one of the Atkins diet is essentially meant to get the metabolism started again to ensure that weight will be lost quickly. While in this stage, only a certain amount of carbohydrates are allowed daily per person. The amount of carbohydrates allowed depends on several factors, but the average daily amount is roughly 20 grams of net carbs, as stated by Atkins on its website.