Chapter 10:
Carbohydrates and the ketogenic diet
In addition to the standard ketogenic diet (SKD), this book also details two modifications
which have been made to the SKD. As discussed in forthcoming chapters on exercise, a SKD
cannot sustain high-intensity exercise performance such as weight training or high-intensity
aerobic training and carbohydrates must be integrated to the SKD in some fashion.
There are two primary types of ‘modified ketogenic diets’ which incorporate carbohydrate
intake within the structure of a SKD. The first of these is the Targeted Ketogenic Diet (TKD) in
which individuals consume carbohydrates around exercise only. This allows for a maintenance of
exercise performance and glycogen resynthesis without interrupting ketosis for long periods of
time.
The second type of ‘modified ketogenic diet’ is the Cyclical Ketogenic Diet or CKD. The
CKD alternates periods of a ketogenic diet (generally 5-6 days) with periods of high carbohydrate
intake (1-2 days).
Typically the TKD is used by those individuals who either can not or will not perform the
longer carb-load of the cyclical ketogenic diet (CKD) or by individuals who are just starting
exercise programs and are not ready to perform the amount of exercise needed to make the CKD
work.
The CKD is typically aimed at individuals who are more advanced in terms of their exercise
programs (i.e. bodybuilders) due to the high volume and intensity of training needed to optimize
the diet. Before discussing the TKD and CKD in chapters 11 and 12, some general comments are
made regarding glycogen levels and rates of glycogen depletion. This chapter discusses glycogen
levels and depletion, topics which apply to both the TKD and CKD.
Section 1: Glycogen levels
To understand the basis of both the TKD and the CKD, a discussion of glycogen levels
under a variety of conditions is necessary. To achieve optimal results from either the TKD or
CKD requires that some estimations be made in terms of the amount of training which can and
should be done as well as how much carbohydrate should be consumed at a given time.
Muscle glycogen is measured in millimoles per kilogram of muscle (mmol/kg). An individual
following a normal mixed diet will maintain glycogen levels around 80-100 mmol/kg. Athletes
following a mixed diet have higher levels, around 110-130 mmol/kg (1). On a standard ketogenic
diet, with aerobic exercise only, muscle glycogen levels maintain around 70 mmol/kg with about
50 mmol/kg of that in the Type I muscle fibers (2,3).
As discussed in greater detail in upcoming chapters, fat oxidation increases, both at rest
and during aerobic exercise around 70 mmol/kg. Below 40 mmol/kg, exercise performance is
impaired. Total exhaustion during exercise occurs at 15-25 mmol/kg. Additionally, when glycogen