The point of a ketogenic diet is to keep blood levels of insulin and glucose as low as possible for as much of the time as possible. The reason is that high levels of each damage the body. Insulin is also the body’s primary fat storage hormone, which if you are overweight or obese, is another reason to keep your insulin level as low as you can.
The principal way to keep insulin low is to eat as little carbohydrate as possible, since carbohydrates are nothing more than chains of glucose molecules, and glucose has a major effect on insulin secretion. It is especially important to avoid sucrose (table sugar) and high-fructose corn syrup, because sucrose is a glucose molecule bonded to a fructose molecue. The glucose molecule will cause your insulin to rise, and too much fructose causes the same kind of damage to your liver that too much alcohol causes.
You can safely eat some carbohydrate, but we recommend no more than 20 g/day. This means sticking to leafy greens and cruciferous vegetables, such as broccoli and cauliflower, because they contain a lot of water and fiber, and not so much digestible carbohydrate. Certain high-fiber fruits, such as strawberries and blueberries, are safe in low quantity. Avocado is also a good fruit to eat on a ketogenic diet, because it contains very little sugar and is a good source of healthy fat.
Basically, your diet should consist mostly of protein and fat, and you should eat enough to satisfy your hunger. We recommend an amount of protein somewhere in the neighborhood of 1.0-2.0 grams a day per kilogram of lean body mass, but if you are still in your growth spurt, that limit does not apply to you. (It’s for adults who have finished growing up and now grow only sideways, lol!) Protein does stimulate insulin secretion, but that’s a good thing, because we do need small level of it in our blood in order to live (Type I diabetics, whose bodies can’t make insulin at all, used to starve to death before insulin was discovered). When we eat very little or no carbohydrate, the insulinogenic effect of protein is enough for survival and not worth worrying about otherwise. Remember that even meat is only about 25% protein, so if you want to eat 100 grams of protein, that would come to about a pound of meat.
Fat is a safe source of calories, because it’s effect on insulin secretion is almost non-existent. You will read many posts here encouraging people to eat more fat. But you should not be stuffing yourself to the gills with fat, you should simply eat enough protein and fat to assuage your hunger, and not eat again until you feel hungry again. If you are eating enough food, you will find yourself going several hours between meals. If you let hunger and satiety be your guide, your body will happily tell you when it needs food and when it doesn’t. This is a lot easier than calculating caloric intake and figuring quantities to eat.
