No it is not necessary to buy Ketostix. However, one of the keys to the diet is being in ketosis. To be able to confirm ketosis is always a moral lift. Also, when switching to the Ongoing Weight Loss and Maintenance parts of the diet where you start to increase your carbohydrate intake, the Ketostix will be able to help you determine where your tolerance level for carbohydrates is. Being able to actually see that you are indeed, in ketosis, usually helps people tremendously, and gives them that extra edge in pursuing their weight-loss goals.