These concerns are difficult to understand in terms of where they originated. What must
be understood is that ketones are normal physiological substances. As discussed in great detail
in chapter 4, ketones provide the brain with fuel when glucose (or food in general) is not available.
The brain develops the enzymes to use ketones during fetal development and these enzymes are
still present as we age (32), which should serve to illustrate that ketones are normal fuels, and
not toxic byproducts of an abnormal metabolism.
Although not a perfect model, epileptic children provide some insight into possible
detrimental long term effects of the ketogenic diet on brain function. Quite simply, there are no
negative effects in terms of cognitive function (30). Except for some initial transient fatigue,
similar to what is reported in adults, there appears to be no decrement in mental functioning
while on the diet or after it is ended.
However, this is not absolute proof that the ketogenic diet couldn’t have possible long-term
effects on the brain ; simply that no data currently exists to suggest that it will have any
negative effects. Anecdotally, individuals tend to report one of two types of functioning while in
ketosis: excellent or terrible. Some individuals feel that they concentrate better and think more
lucidly while in ketosis ; others feel nothing but fatigue. Differences in individual physiology may
explain the difference.
With regard to short term memory loss, the only study which remotely addresses this
point is a recent study which showed temporary decrements in a trail-making task (which
requires a high degree of mental flexibility) during the first week of a low-calorie ketogenic diet as
compared to a non-ketogenic diet (33). The majority of the effects were seen during the first week
of the diet, and disappeared as the study progressed.
As stated previously, some individuals do note mental fatigue and a lack of concentration
during the first 1-3 weeks of a ketogenic diet. In practical terms, this means that individuals who
operate heavy machinery, or need maximum mental acuity for some reason (i.e. a presentation
or final exam) should not start a ketogenic diet during this time period.
Uric acid levels
Uric acid is a waste product of protein metabolism that is excreted through the kidneys.
Under normal circumstances, uric acid is excreted as quickly as it is produced. This prevents a
buildup of uric acid in the bloodstream which can cause problems, the most common of which is
gout. Gout occurs when urate cause deposit in the joints and cause pain.
High levels of uric acid in the bloodstream can occur under one of two conditions: when
production is increased or when removal through the kidneys is decreased. The ketogenic diet has
been shown to affect the rate of uric acid excretion through the kidneys.
Ketones and uric acid compete for the same transport mechanism in the kidneys. Thus
when the kidneys remove excess ketone bodies from the bloodstream, the removal of uric acid
decreases and a buildup occurs.
Studies of the ketogenic diet and PSMF show a consistent and large (oftentimes doubling or
tripling from normal levels) initial increase in uric acid levels in the blood (24,26). In general
however, levels return towards normal after several weeks of the diet (35). Small amounts of