carbohydrates (5% of total daily calories) can prevent a buildup of uric acid (35). Additionally, in
studies of both epileptic children as well as adults the incidence of gout are very few, and only
occur in individuals who are predisposed genetically (12, 26,34).
Related to this topic, uric acid stones have occasionally been found in epileptic children
following the ketogenic diet (36). This appears to be related to high levels of urinary ketones, low
urinary pH and fluid restriction in these patients. It is unknown whether individuals consuming
sufficient water on a ketogenic diet have any risk for this complication.
From a practical standpoint, individuals with a genetic predisposition towards gout should
either include a minimal amount of carbohydrates (5% of total calories) in their diet or not use a
ketogenic diet.
Kidney stones and kidney damage
A common concern voiced about ketogenic diets is the potential for kidney damage or the
passing of kidney stones, presumably from an increase in kidney workload from having to filter
ketones, urea, and ammonia. As well, dehydration can cause kidney stones in predisposed
individuals. Finally, the ‘high-protein’ nature of ketogenic diets alarms some individuals who are
concerned with potential kidney damage.
Overall there is little data to suggest any negative effect of ketogenic diets on kidney
function or the incidence of kidney stones. In epileptic children, there is a low incidence (~5%) of
small kidney stones (22,30). This may be related to the dehydrated state the children are
deliberately kept in rather than the state of ketosis itself (22).
The few short term studies of adults suggest no alteration in kidney function (by
measuring the levels of various kidney enzymes) or increased incidence of kidney stones, either
while on the diet or for periods up to six months after the diet is stopped (26). Once again, the lack
of any long term data prevents conclusions about potential long-term effects of ketosis on kidney
function.
With regards to the protein issue, it should be noted that kidney problems resulting from a
high protein intake have only been noted in individuals with preexisting kidney problems, and little
human data exists to suggest that a high protein intake will cause kidney damage (37). From a
purely anecdotal standpoint, athletes have consumed high protein diets for long periods and one
would expect kidney problems to show up with increasing incidence in this group. But such an
increase has not appeared, suggesting that a high protein intake is not harmful to the kidneys
under normal circumstances (37).
However, much of this is predicated on drinking sufficient water to maintain hydration,
especially to limit the possibility of kidney stones. Individuals who are predisposed to kidney
stones (or have preexisting kidney problems) should consider seriously whether a ketogenic diet is
appropriate for them. If they do choose to use a ketogenic diet, kidney function should be
monitored with regular blood work to ensure that no complications arise.