Classic or classical ketogenic diet? Definitions and nomenclature

Dr. Ruby M. Schwartz coined the term "classical" ketogenic diet (KD) in 1989, followed by Dr. Stephen L. Kinsman in the USA, who introduced the term "classic" KD in 1992. Over the next decade, the term "classic KD" became increasingly common. So, which term is preferable-classic or classical? Given the widespread usage, we advocate for consistently using "classic KD." As there is also significant ambiguity about what exactly defines the classic KD compared to other diets, we believe two key aspects are required for the definition of classic KD: the principle of administration and the minimum ketogenic ratio (grams of fat to carbohydrates and protein). Classic KD studies emphasize a tailored, individualized approach to caloric intake and macronutrient distribution, with food items precisely measured. This personalized prescription is the defining feature of classic KD. Recent studies have proposed lower ratios, such as 2:1 or 2.5:1, yet the modified Atkins diet, introduced 80 years later, shows that a 1:1 ratio or lower can also induce ketosis. Therefore, labeling a classic KD with a minimum ratio of 3:1 or 4:1 is misleading. We contend that the classic KD should primarily be defined by its precise, individualized ratios, rather than by an arbitrary minimum value.