Objective: To evaluate the effect of a low-carbohydrate, ketogenic diet (LCKD) on weight loss and side effects.Background: Many Norwegian embrace the “Ketolytic diet” (<20g carbohydrates/day), even if they know little of nutrition and although this diet is yet not scientifically proved. Methods: I performed MEDLINE search for English language studies, with the key words Ketogenic diet, Very low carbohydrate diet and weight loss. I included articles describing randomized, controlled trials comparing LCKD with other diets in overweight adults. Only articles that allowed ad libitum intake of fat, protein and calories, were included. Fourteen articles matched the inclusion criteria, reporting data for 1089 participants.Results: The studies produced results on weight loss, serum lipids, glucose, insulin, insulin sensitivity/-resistance, HbA1c, blood pressure, positive side effects and adverse effects, and thus gave results on diabetes II, the metabolic syndrome and cardiovascular risk factors. Discussion: In many studies blinding of personnel and description of the randomization procedure were absent. A high dropout rate and bad compliance seemed to be a problem. In some studies the groups were not treated equal. Unfortunately many studies did not say if the changes compared to baseline were significant. For some of the results the data were too small to make conclusions.Conclusion: LCKD seems to have a better impact than other diets on weight, triglyceride, LDL-profile (with exceptions), HDL, diabetes II and metabolic syndrome. All diets seem to improve the level of total cholesterol and blood pressure. LCKD does probably give more adverse effects than other diets.