OBJECTIVE: To evaluate the long term efficacy and implications of the low carbohydrate diets, especially the ketogenic variant, with respect to weight loss, changes in metabolism and mental effects.BACKGROUND: The low carbohydrate diets are a hot topic in the Norwegian media and a significant part of the population is, or has been, under a carbohydrate restricted diet.METHODS: Properly described problems were chosen and a MEDLINE search was done to find publications fitting the given problem. Search terms were low carbohydrate ketogenic diet paired with either weight loss, metabolic or mental. 16 publications with a variation of foci between the three main groups of problems were included .RESULTS: Both the low carbohydrate ketogenic diet (LCKD) and the conventional low fat diet (LFD) proved to be efficient in reducing weight compared to baseline. The LCKD implied a greater weight loss during the first six months with results flattening after twelve and 24 months. LCKD was followed by an increase in total cholesterol, VDL and HDL and a decrease in triglycerides compared to LFD. The LCKD participants reported significantly less hunger and showed less appetite while eating freely than did the LFD group.DISCUSSION: Many studies failed to blind the personnel doing the measuring. There is also generally high drop out rates. Another problem that may be raised is the fact that many trials have economic association to The Robert Atkins Foundation.CONCLUSION: LCKD presents itself as a real alternative to the conventional LFD. For patients not reaching their goals with the LFD, a LCKD may be an alternative to reach a desired weight loss. More research needs to be done, however, into what metabolic changes such a diet implies. We do not yet know what direct and indirect effects the low carbohydrate diets have on more strict outcomes like mortality or myocardial infarction.