Potential Side Effects of the Ketogenic Diet
The ketogenic diet is not recommended for cancer patients or individuals at risk of malnutrition due to its potential to induce or aggravate malnutrition through its highly restrictive nature and low palatability, which may lead to insufficient energy intake and weight loss. 1
Common Side Effects
Short-term Side Effects (Initiation Phase)
Gastrointestinal Effects
- Digestive system disorders 3
- Constipation
- Diarrhea
- Nausea
- Potential risk of pancreatitis (rare but serious) 2
- Protein-losing enteropathy (rare but serious) 2
Metabolic and Cardiovascular Effects
- Potential worsening of lipid profile 3, 4
- Potential prolonged QT interval (rare but serious) 2
- Risk of cardiomyopathy (rare but serious) 2
- Potential for fat-free mass loss 4
Nutritional Deficiencies
The ketogenic diet can lead to:
This is particularly concerning because the diet is highly restrictive in the type and quantity of specific foods, generally restricting food intake overall 1.
Special Risk Populations
Cancer Patients
The ESPEN guidelines strongly recommend against ketogenic diets for cancer patients, stating:
- No clinical trials demonstrate a benefit of ketogenic diets in cancer patients 1
- Low palatability may lead to insufficient energy intake and weight loss 1
- Increases risk of malnutrition in already vulnerable patients 1
Diabetic Patients
- Requires medical supervision, especially for those on insulin or SGLT2 inhibitors
- Risk of ketoacidosis 5
Children with Epilepsy
While therapeutic in this population, children require careful monitoring for:
- Blood counts
- Liver enzymes
- Renal function
- Vitamin and mineral levels
- Lipid profiles
- Serum carnitine levels 2
Long-term Considerations
The ketogenic diet's long-term effects remain inadequately studied:
- Its efficacy for weight loss is not significant in long-term observations 4
- Low-carb patterns are more beneficial than very low-carbohydrate (including ketogenic) diets in terms of cardiovascular mortality 4
- Further studies to determine long-term effects are required 3
Monitoring Recommendations
For those following a ketogenic diet for medical purposes:
- Blood ketone levels between 0.5-3.0 mmol/L indicate nutritional ketosis
- Levels above 3.0 mmol/L may require medical attention, especially in diabetic patients 5
- Regular monitoring of nutritional status and metabolic parameters is essential
Important Caveats
- The ketogenic diet does not fulfill the criteria of a healthy diet 4
- There are no diets known to reproducibly cure cancer or prevent cancer recurrence 1
- Many claims supporting extreme dietary regimens like the ketogenic diet are not based on scientific reasoning or solid evidence 1
- Compliance for following extreme dietary regimens is generally low 1
While some recent research suggests potential benefits for weight loss and metabolic parameters in the short term 6, 7, the significant risks and side effects warrant careful consideration, especially for vulnerable populations.