Dangerous. Your brain and red blood cells need glucose to function at their best. When you don't consume enough carbs, your body breaks down muscle to supply the needed glucose. Only carbohydrate and protein can be used to produce glucose (fats cannot produce glucose). So when you don't consume enough carbohydrate, your body uses muscle mass for gluconeogenesis. So you lose muscle mass, which you do not want, as muscle is a metabolically active tissue - the more muscle mass you have, the more calories you burn, even at rest. While ketogenic diets may be used for epilepsy that doesn't respond to other treatments, it is done with close medical supervision and advice from a registered dietitian to ensure that the diet is nutritionally adequate.
In the short term, all diets work, regardless of the macronutrient composition, because people are paying closer attention to the foods that they consume. In the long run, changes that can be sustained are important, as most people regain the weight they lost if they haven't made sustainable changes.
From research, we know that most people regain the weight they lost after following "fad" diets, and the ketogenic diet is a fad diet. Sadly, many people end up at a higher weight! And we know that weight cycling (repeatedly losing and regaining weight) is even more dangerous than being obese!
Long term, sustainable weight loss is only achieved by making lifestyle changes that can be continued for the rest of the individual's life. For some people that may mean a low healthy fat diet, for others it may mean a low carb diet (but never as low as that advocated by the keto diet). Following something like the healthy plate model (half of your plate should be fruits and vegetables, a quarter grains and starches, a quarter protein, with minimal added sugars and just enough healthy fats to obtain your essential fatty acids) has been shown to have better long-term success in terms of both weight maintenance and health, than any fad diet out there.
The research basically says: in the short term, ALL diets work. In the long term, weight loss / maintenance only occurs in those who are able to make dietary changes that they can sustain for the rest of their lives. And regardless of what changes are made, lifestyle changes (i.e. diet and exercise) can, at most, allow an individual to lose 10% of their initial staring weight. It's been shown time and time again in research studies. Improving health, however, can be attained with lifestyle changes, even in the absence of significant weight loss.
Caylynn, RD, MPH
