A lot of what's out there tend to ignore or gloss over the science (that's true for most diet trends), but the ketogenic diet can be traced back to the 1920's, when it was developed as a diet for controlling epilepsy, before the drugs that are mostly used today were developed.
The basic principle is to keep the carbs consumed down while raising the amount of protein and, especially, fat. How low you have to get varies from person to person, generally below 50 carbs/day, though 20-30 is more likely to be successful.
Once the body uses up its reserves of glycogen (about 3 days worth, stored mostly in the liver and also in muscles), it will start converting fat to glycogen for energy. This is called ketogenesis. The trick is to avoid getting your ketones too high, which can turn the blood acidic, and is called ketoacidosis. It can be fatal. But there's a pretty wide range of ketone numbers where you're in ketogenesis before that happens.
There are multiple ways to test your ketones, some are better (or at least more accurate) than others.
Some of the proponents of the keto diet or its offshoots tend to get preachy, telling you to avoid most of the meats and other proteins in stores for reasons that have nothing to do with ketogenisis, eat only organic foods, avoid all gluten, etc.
A cyclical ketogenic diet should be a bit more flexible, allowing some carbs, even (oh, the shame of it all!) wheat. 🙂
Because fats are taste bombs, a ketogenic diet can be very tasty and filling. (Fats also fill you up faster and leave you more satisfied than carbs.)
Tonight, for example, we had a cheese souffle with mushroom sauce, using some almond flour and xanthan gum, cream (watered down), eggs, butter, cheddar cheese and mushrooms. A serving was probably 4-5 carbs (I'm checking it using multiple recipe analysis tools), and it was delicious! By comparison, my traditional souffle recipe (served with canned mushroom soup as a sauce) is more like 30-40 carbs/serving.
Being an engineer by training, I think I'll read some of the scientific papers on ketogenesis as we get further into this, but I don't claim that I'll fully understand them.
