You want another food, but you only eat buckwheat, and therefore you cannot eat its normal amount. Thus, there is a strong lack of calories from food, and the person loses weight. In order not to break away ahead of time, the diet is supplemented with kefir, which also does not have significant caloric content. Problems buckwheat diet as much as any mono-diet. Restricting the diet to 1-2 foods is fraught with low diet efficiency. Even if you lose weight on the buckwheat diet, you cannot keep the result after the rejection of such a diet plan.