Cyclical Ketogenic Diets Part 1
Copyright Lyle McDonald 1996
Abstract
After roughly a 20 year absence from the public eye, the ketogenic diet
has made a reappearance in both the fields of weight loss as well as sports
nutrition. Books like "Dr. Atkins New Diet Revolution", "Protein Power" by
the Eades', and to a lesser degree "The Carbohydrate Addicts Diet" by the
Hellers have brought low carb dieting back into the weight loss arena.
Additionally, in the field of sports nutrition, two slightly different
approaches have entered the fray in the form of "The Anabolic Diet" created
by Dr. Mauro DiPasquale and "Bodyopus" created by Dan Duchaine. Rather
than suggesting a low carbohydrate approach indefinitely, these two diets
advocate a cyclical ketogenic approach combining 5 days of low carbohydrate
intake with a 2 day carb-up akin to what endurance athletes used to do
prior to competition.
Unfortunately, it is difficult to draw any absolute conclusions about this
approach from article written about it as the groups involved in the debate
invariably have some vested financial interest in either promoting or
decrying the approach. In this article, I simply want to examine some of
the theoretical bases of the cyclical ketogenic diet and if it has any
merit. Additionally, possible health concerns will be discussed.
Some Basic physiology
What are ketones?
Ketone or ketone bodies (KB) are a byproduct of fat metabolism. KB's are
generated in the liver due to the actions of glucagon (15). There are two
KB's which circulate freely in the bloodstream. They are acetoacetate and
beta-hydroxybutyrate. Most aerobic tissues, including the brain, skeletal
muscle, and the heart can oxidize KB's for fuel (8). Under normal blood
sugar conditions, glucose is the preferred fuel in the brain, muscles and
heart. Under these conditions the rate of ketone body utilization by
tissue depends in part on their concentration. Under normal conditions, KB
metabolism is minimal, perhaps 1-2% of total energy expenditure. In
diabetic ketotic patients, this can increase to 5% (8).
Glucagon, insulin and ketogenesis:
The formation of KB's and utilization of fuel is ultimately controlled by
the circulating levels of insulin and glucagon. Insulin is a hormone
released from the pancreas in response to eating carbohydrates. Glucagon
is insulin's antagonistic hormone and is only present when insulin levels
fall to quite low levels. In the liver, high glucagon levels direct FFA
away from TG synthesis and towards beta-oxidation. Glucagon also activates
adipose tissue lipase which activates lipolysis. Glucagon's ketogenic and
lipolytic effects are inactivated by even small amounts of insulin. To
achieve sufficient glucagon concentrations for increased
ketogenesis/lipolysis, blood glucose levels must drop to around 50-60 mg/dl
and insulin must drop almost to zero. This drop in insulin can occur with
complete fasting, exercise, or by simply restricting carbohydrate intake to
below 30 grams per day. Within about 3 days of carbohydrate restriction,
blood glucose will fall below 60 mg/dl, insulin levels will drop to zero
and glucagon levels will increase causing an increase in KB formation.
With exercise training, ketogenesis should occur more quickly and ketosis
established. (2)
How to induce ketosis?
Ketosis (defined as the buildup of the KB's in the bloodstream) will occur
under several conditions including: fasting, after prolonged exercise, and
when a high fat diet is consumed. (7,8,15).
Once ketosis is established (i.e. when ketone concentration in the blood
is higher than glucose concentration), ketones will become the preferred
fuel by all three tissues providing up to 75% of the fuel utilized (7).
The brain, which normally utilizes glucose exclusively for fuel will, after
a period of 2 to 3 weeks, switch almost exclusively to using KB's for fuel
(1, 6, 15). The time delay for the brain to make this metabolic shift has
some major implications which need to be discussed. As described further
below, one study (22) found a decrement in mental flexibility during the
first week of adopting aketogenic diet. Therefore, for individuals who's
jobs or livelihood requires great mental acuity, the ketogenic diet
approach (cyclical or otherwise) may not be an ideal one.