great range of responses among individuals on a ketogenic diet. Some show a drastic decrease in
cholesterol while others shown an increase.
Changes in blood TG levels are also common on the ketogenic diet. Somewhat
counterintiuitively, there is generally a decrease in blood TG levels, (28) which may indicate
greater uptake of TG by tissues such as skeletal muscle.
Since no absolute conclusions can be drawn regarding cholesterol levels on a ketogenic diet,
dieters are encouraged to have their blood lipid levels monitored for any negative responses.
Ideally, blood lipid levels should be checked prior to starting the diet and again 6-8 weeks later. If
repeat blood lipid tests show a worsening of lipid levels, saturated fats should be substituted with
unsaturated fats or the diet should be abandoned.
Low energy levels
Carbohydrates are the body’s preferred fuel when they are available (see chapter 4). As
well, they burn more efficiently than fats. Many individuals voice concerns about drops in general
energy levels (not including exercise) on a ketogenic diet due to the lack of carbohydrates.
Many subjects in early studies on ketosis or the PSMF noted transient lethargy and
weakness. As well many studies noted a high occurrence of orthostatic hypotension which is a
drop in blood pressure when individuals move from a sitting to standing position. This caused
lightheadedness in many individuals. It was always taken for granted that ketosis caused this to
happen.
However, later studies established that most of these symptoms could be avoided by
providing enough supplemental minerals, especially sodium. Providing 4-5 grams of sodium per
day (not much higher than the average American diet) prevents the majority of symptoms of
weakness and low energy, possibly by maintaining normal blood pressure (26).
In most individuals fatigue should disappear within a few days to a few weeks at most. If
fatigue remains after this time period, small amounts of carbohydrates can be added to the diet,
as long as ketosis is maintained, or the diet should be abandoned for a more balanced diet.
The effects of ketogenic diets on exercise are discussed in chapter 22. To summarize,
ketogenic diets can generally sustain low-intensity aerobic exercise without problem after a
period of adaptation. However because carbohydrates are an absolute requirement to sustain
high intensity exercise such as weight training or high-intensity aerobic exercise, a standard
ketogenic diet is not appropriate.
Effects on the brain
A well known effect of ketogenic diets is the increased use of ketones by the brain (29). As
well, some of the effects of the ketogenic diet in treating childhood epilepsy may be due to this
increased extraction of ketones (30,31). Due to the changes which occur, a variety of concerns
has been voiced in terms of possible side-effects. These include permanent brain impairment and
short term memory loss.