Side effects of Ketogenic Therapy

Early side effects

During initiation of ketogenic therapy there is a risk of hypoglycaemia, acidosis, dehydration and high levels of ketones (1). Children on carbonic anhydrase inhibitor medications (for example, topiramate or zonisamide) may have increased risk of excess ketosis and metabolic acidosis on commencing ketogenic therapy (2).

Nutrition and growth

Children with drug resistant epilepsy are at risk of insufficient vitamin D status prior to starting ketogenic therapy (3) and although levels can be normalised with vitamin D supplementation, a decline in both whole body and spine bone mineral content while on the ketogenic diet has been reported (4) despite reduction in anticonvulsant medication. Selenium deficiency can occur in children on the ketogenic diet (5) with risk of impaired myocardial function (6). Low plasma magnesium has also been reported (1) and may be a particular problem in children on the classical diet despite micronutrient supplementation (7). Vitamin C deficiency was found in one child on the ketogenic diet (8) but plasma levels of fat soluble vitamins A and E can often be raised as a consequence of a high fat intake (7). A fall in carnitine status of children and young adults during the first few months of the ketogenic diet has been seen with some cases requiring supplementation (9), although levels tended to normalise with time on diet therapy.

There is evidence of impaired growth in children on the ketogenic diet (10, 11, 12); younger children may be more at risk (13). Despite the higher protein allowance of the medium chain triglyceride (MCT) diet, no differences were seen in the growth of children on this diet compared to the lower-protein classical diet (14). Long-term follow up of children treated with the ketogenic diet in the past suggests that although growth does improve after diet treatment is discontinued, height gain can still be below expected (15).

Individual requirements for vitamin, mineral and trace element supplementation must be monitored by a dietitian. A child’s growth should be regularly assessed while on ketogenic therapy taking into account that children with neurological disability will often have growth measurements that fall well below the expected for age.


Elevated blood cholesterol and triglyceride levels have been reported in children on the ketogenic diet with significant increases in atherogenic apoB-containing lipoproteins (16). Raised blood lipids may trend back to normal with time on treatment (17) and dietary modifications can also help to achieve healthy levels (18).  The full assessment of cardiovascular risk requires investigation of any physiological changes in the function of the arteries.  Results suggest that while arterial stiffness may increase initially on the ketogenic diet (19), the changes in arterial function observed within the first year of treatment are not significant after 24 months and appear to be reversible (20).

Kidney stones

The reported incidence of kidney stones in children on the ketogenic diet is higher than that of the general paediatric population. Uric acid, calcium oxalate, calcium phosphate or mixed composition stones have been reported in up to 7% of children on the diet (21, 22, 23). Risk may be higher with long-term treatment (12) and concurrent use of carbonic anhydrase inhibitors such as topiramate or zonisamide (24).


Gastro-intestinal problems are common side effects of ketogenic therapy however can usually be alleviated with dietary manipulation.  Vomiting, nausea, diarrhoea, and abdominal discomfort have been reported in studies of the MCT (25, 26) and classical ketogenic diets (1). There is a risk that children with pre-existing gastro oesophageal reflux will have symptoms exacerbated by a high fat regime. Constipation is the most common reported complication of ketogenic therapy; despite dietary changes to help lessen the problem many individuals do need additional treatment with medication.

Other side effects

Other rare side effects that have been reported with ketogenic therapy are increased infection risk, bruising, raised uric acid in the blood, bone fractures, pancreatitis, lipid-aspiration pneumonia, and cardiac abnormalities (1, 6, 27, 28, 29). Ketogenic diet-induced toxicity of the anticonvulsant medication sodium valproate has been reported (30) however these treatments can be used together without problem in most cases (31).

Modified diets

The literature on side effects of ketogenic therapies has mainly studied traditional ketogenic diets. The limited reports of complications arising from use of the modified Atkins diet (MAD) or low glycaemic index treatment suggest fewer and less serious adverse events when these more liberal modified diets are used (32, 33, 34, 35), although a prospective review of 6 MAD studies found 13% of 92 children and adults discontinued the diet due to intolerance or side effects (36).


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