Less than 30–50 g of carbohydrates per day; pay attention to protein, fiber, and electrolytes.
Randomized pilot trial (47 patients with Parkinson's, 8 weeks): both the low-fat diet and the ketogenic diet improved symptoms; the ketogenic diet improved non-motor symptoms more. Small, preliminary study.
View the study (study) →⏱ 4 min read
The ketogenic diet is a dietary pattern characterized by a very significant restriction of carbohydrates (typically less than 30-50 g/day), a moderate protein intake (1.2-2.0 g/kg/day), and a high fat intake (covering 70-80 percent of total calories); this composition forces the body to produce and use ketone bodies (especially beta-hydroxybutyrate, acetoacetate, and acetone) as its main fuel instead of glucose, a metabolic state called nutritional ketosis that partially reproduces the metabolism of prolonged fasting and that has specific clinical applications with support of varying quality depending on the indication.
The clinical indication with the strongest support and the most historical one is pediatric refractory epilepsy: the classic ketogenic diet with a 4:1 ratio (4 g of fat for every 1 g of protein + carbohydrate combined) and its variants (modified Atkins, low glycemic index) are established treatments in pediatric epilepsy refractory to antiepileptic drugs, with reductions of 50 percent or more in seizure frequency in approximately half of patients; these diets are prescribed under specialized medical and strict nutritional supervision in specialized epilepsy centers, and are not the same as the popular "ketogenic" diets for weight loss.
In weight loss, several trials have documented significant losses, sometimes faster than with traditional low-fat diets during the first 3-6 months; however, at 12-24 months, results even out between diets when adjusted for adherence, and the long-term sustainability of the strict ketogenic diet is relatively low for most people; the ketogenic diet is a useful tool for some people but is not universally superior to other well-implemented weight-loss strategies.
In type 2 diabetes, several studies have documented significant improvements in blood glucose, glycated hemoglobin, and, in some cases, remission of diabetes with a supervised ketogenic diet over months to 1-2 years, with magnitudes in some cases greater than those of standard pharmacological treatments; the Virta Health trial and other studies have generated significant clinical interest in this indication, although it requires strict medical monitoring to adjust medication (especially insulin and secretagogues) and prevent hypoglycemia.
In neurodegenerative diseases (Alzheimer's, Parkinson's, ALS), cancers with specific glycolytic dependence (glioblastoma), and other conditions, the ketogenic diet is under investigation with preliminary data of varying quality; the line of research is active but robust clinical data for these indications are still limited.
Healthy fats (extra virgin olive oil, avocado, nuts, oily fish, seeds) should be the basis of fat intake; saturated and excessively processed fats are problematic in any dietary pattern, including the ketogenic diet; adequate protein intake (1.2-2.0 g/kg/day) is important for preserving muscle mass; low-glycemic-index vegetables (especially leafy greens, cruciferous vegetables, zucchini, bell peppers) should be abundant to ensure intake of fiber, vitamins, and minerals; hydration and adequate electrolyte intake (especially sodium, potassium, magnesium) are critical during initial keto-adaptation; the initial side effects ("keto flu" with headache, fatigue, irritability) are temporary and are minimized with good electrolyte intake.
Practical implementation requires careful planning: counting carbohydrates (less than 30-50 g/day), prioritizing healthy fat sources, maintaining adequate protein, and progressively adjusting amounts according to individual response; the optimal duration varies by indication (3-6 months for weight loss, indefinite under supervision for refractory epilepsy); "cycling" between ketogenic and Mediterranean periods is an option for people who prefer not to maintain ketosis indefinitely.
Safety considerations are important: the ketogenic diet is contraindicated in people with porphyria, specific enzymatic defects in ketone body metabolism (carnitine deficiency, primary pyruvate carboxylase deficiency, others), acute pancreatitis, severe liver disease, pregnancy and breastfeeding (except under very specific medical supervision), and active eating disorders; people with type 1 diabetes should take special care because of the risk of diabetic ketoacidosis (distinct from nutritional ketosis but clinically confusable); people with type 2 diabetes on pharmacological treatment require medication adjustments supervised by endocrinology; people with specific familial dyslipidemia may have worsening LDL with a ketogenic diet rich in saturated fats; medical follow-up during initial implementation and, ideally, throughout treatment is prudent; ultraprocessed commercial "keto" products are often inadvisable despite the label (unfavorable biochemical profile, problematic ingredients); the reasonable clinical stance is: the ketogenic diet is a valid clinical tool for specific indications (refractory epilepsy, some specific cancers, supervised type 2 diabetes, weight loss in selected people who tolerate and prefer it), but it is not universally superior to the Mediterranean diet for most population health goals.
Information, not medical advice. Scientific evidence reflects the quality of the studies.