Liver damage
Another concern often raised is for the potential negative effects of a ketogenic diet on the
liver. In one of the few longer-term (4 weeks) studies of the ketogenic diet, liver enzymes were
measured and no change was observed (26). Additionally, no liver problems are encountered in
epileptic children. However, it is unknown whether negative effects would be seen in the longer
term.
Constipation
Arguably one of the more common side-effects seen on a ketogenic diet is that of reduced
bowel movements and constipation (30,34). In all likelihood, this stems from two different
causes: a lack of fiber and increased gastrointestinal absorption of foods.
First and foremost, the lack of carbohydrates in a ketogenic diet means that fiber intake
will be low unless supplements are used. There is no doubt that fiber is an important nutrient to
human health. A high fiber intake has been linked to the prevention of a variety of health
problems including some forms of cancer and heart disease.
To make a ketogenic diet as healthy as possible, some type of sugar-free fiber supplement
should be used. In addition to possibly preventing any health problems, this will help to maintain
bowel regularity. Many individuals find that a large salad containing fibrous vegetables may help
with regularity and should fit easily with the 30 gram carbohydrate limit.
One interesting effect of the ketogenic diet is the typically reduced stool volume seen (30).
Presumably this is due to enhanced absorption/digestion of foods which leads to less waste
products being generated (22).
Vitamin/mineral deficiencies
The restricted food choices of a ketogenic diet raise concerns about possible deficiencies in
vitamin and mineral intake. Any diet which is restricted in calories, whether ketogenic or not, will
show a decrease in micro-nutrient intake compared to a similar diet at higher calories. So the
question is whether the ketogenic diet is more or less nutritionally adequate compared to a
‘balanced’ diet at the same calorie level. While this is a fairly moot point for those who have
already decided to use a ketogenic diet, it is important to examine, if for no other reason than to
know what nutrients should be supplemented to the diet.
It is difficult, if not impossible, to obtain adequate micro-nutrients on any diet containing
less than 1200 calories per day (37). To a great degree, micro-nutrient intake is affected by total
caloric intake regardless of diet. That is, a diet containing 400 calories will have less micro-
nutrients that one containing 2000 calories regardless of composition. Therefore, let us look at
nutrient intake relative to caloric intake (amount of nutrient per calorie).
One researcher did exactly this, comparing nutrient intakes of his low-carbohydrate diet to
the subject’s normal diet (39). He then examined how much micronutrient intake would be
affected if the subject’s normal diets were reduced to the same caloric level as they consumed on