Ketogenic weight-reduction dieting methods have existed since antiquity. Recent research has demonstrated their value in controlling type 2 diabetes. Although research done in the 1920s provided a mathematical model of non-weight-reduction ketogenic clinical diets using the concept of a ketogenic ratio (KR), little has been done to evaluate the ketogenic nature of purported ketogenic weight-reduction diets. The mathematical model of Woodyatt is valid only under isocaloric conditions where dietary energy intake is balanced by energy use. It is hypothesised that under certain conditions of weight loss, energy deficit can predict utilization of stored lipid so that a modified formula for total ketogenic ratio (TKR) may be derived. Such a predictive mathematical model may be a useful tool in predicting the efficacy of weight-reduction diets and adapting such diets to individual patient needs.