How it works:
The Ketogenic diet refers to a high fat, low carb diet designed to promote nutritional ketosis, or the use of ketone bodies for fuel. Ketone bodies are formed from fat, and as such, promotes a greater degree of fat burning in the body.
There is some promise of very significant benefits while on the ketogenic diet. One is that your body is more often in a "fat-burning" mode. There is a fair amount of evidence to suggest that your brain will run more optimally on ketones once that switchover is made from glucose. Because there are no large-scale influxes of carbohydrate, your blood sugar, and thus your energy and mood would remain more stable.
Anytime you are drastically switching your style of eating, it takes time for your body to adapt. There is a phenomenon known as the "keto flu" wherein people experience feelings of nausea, brain fog moodiness, irritation, cramps, fatigue, and diarrhea as the body adjusts to the extremely high fat, low carb content. There will also be a dip in the person's athletic performance as they are no longer sufficiently consuming the main source of fuel for high-intensity performance, carbohydrates.
The ketogenic diet has some great upside in terms of those searching for fat burning and mental acuity. Getting into a ketogenic state is not said to be a pleasant experience, but most of that does go away and you are left with the benefits. For this reason, I see it as being appropriate for those who are overweight and obese (with an extra thumbs up for diabetics) and are either sedentary or lightly active. I do not find this to be an appropriate diet solution for those who do high-intensity exercise. While the average person doesn't necessarily need a high-carb diet, they do need enough to support their activity level, and that is not supported by this diet. Basically eliminating a macronutrient is, in my opinion, always a losing battle for those who don't live their lives as a lab experiment, and therefore not sustainable for the long-term. Yes, this will help you lose fat, but there is so much more that goes with healthy living that I can't see myself recommending it for more than a short period (< 6 months), and probably only to those people that I listed above. Most people will get much more out of a balanced diet that looks like this,