What is it? The ketogenic diet is a diet that severely restricts carbohydrate consumption to about 20-50 g/day in order to establish a state of ketosis. (For reference. The recommended consumption of carbs for a 1500 calorie diet is about 150-200 g/day). Our cells preferred source of energy is glucose (aka blood sugar), which comes from the carbs we eat in our diet. In the absence of carbs, glucose will deplete after about 2-3 days and the body will start to break down fat stores to produce ketone bodies and use that as the main source of energy. It’s at this point the body is in a state of ketosis and solely burning fat for energy. It's this "fat burning" mechanism that is the draw for the weight loss industry.
History: The keto diet started as a therapeutic diet in the clinical setting to treat children with epilepsy. Since our brains prefer and almost exclusively use glucose for energy, researchers found episodes of seizures went down significantly when carbs were nearly eliminated in the diet. This approach in many cases is just as effective as medications and is still used today as an effective treatment for epilepsy. There are on-going studies looking at the effectiveness of the ketogenic diet in treating other illnesses including cancer and a number of other neurological illnesses.
Keto for weight-loss: Several studies have shown that weight loss can be achieved when eating a keto diet. Similar results have been found when looking at a variety of other diets including low carb, low fat and low calorie diets. However, most studies show weight re-gain after several months, or when the diet adherence goes down. As with any “diet’ the moment you stop following it, is the moment you’re likely to start gaining the weight back.
Is keto healthy for generally healthy people? By following a strict keto diet, you will be restricting or nearly eliminating an entire macro-nutrient group, carbohydrates. In this case there is certainly concern for nutrient deficiencies which, at the very least should be monitored and supplemented appropriately. The keto diet contains high fat and high protein foods, from both animal and plant sources. Nutrients like potassium, calcium, magnesium, folate and vitamin C are nearly impossible to get through animal protein sources and plant fats without supplementation. Restricting carb intake to 20 g is the equivalent to eating half of a banana or about 10 crackers per day. Foods like grains, most vegetables, fruits, beans and legumes must be avoided in order to attain this level of carb restriction. Furthermore, humans have a physiological protein ceiling, which is the limit of our liver’s ability to up-regulate enzymes necessary for urea synthesis, necessary to safely digest and process high protein intake. This limit is typically 30-40% of our calories coming from protein. In a keto diet, protein it typically much higher. Long term adherence of the keto diet has also been shown to develop of Non-Alcoholic Fatty Liver Disease signatures and systemic glucose intolerance in liver and adipose tissue. Additional studies have also shown decreased performance in athletes due to the significantly low levels of muscle glycogen stores (or glucose stores in the muscle).
Additionally, countless non-keto focused research provides overwhelming evidence that the Mediterranean diet, a mostly plant based diet with very little red meat and saturated fat is the accepted healthy diet for long term health. The health claims of the ketogenic diet conflicts with endless research published and replicated over decades of time in this field supporting a mostly plant based, moderate carb diet.
My takeaway: As a evidence-based Registered Dietitian, I would not recommend the keto diet to any generally healthy individual for weight loss or any other reason. At this time epilepsy is the only well documented illness with substantial evidence that shows it can be improved or managed by following a ketogenic diet.