W. C. Fields, in “My Little Chickadee”: “I always keep a bottle of whiskey handy, in case of snake bite. I also carry a large snake. . . .”
@Geesee People have largely filled you in, but here are a couple of other data that you might have missed: First, macro percentages are always percentages of total calories, not of total weight. Since a gram of fat contains 9 calories and a gram of protein 4, this means that an equal amount of fat and protein is actually about 61% fat and 39% protein, in terms of calories. So it’s easier to get enough fat than you may have been thinking.
But the real point is this: insulin is the fat-storage hormone of the human body, par excellence. To metabolize any excess fat that may be hanging around, and for general all-round metabolic health, the body needs to minimize insulin secretion, and the only way to do that effectively is to eat an absolute minimum of carbohydrate. So staying under the 20 g/day limit that we advise will lower your insulin, put you into nutritional ketosis, and eventually will lead to your becoming fat-adapted.
But where are you going to get all the calories you need once you stop eating carbohydrate? Why, from fat, of course, since fat is the least insulinogenic of the three macronutrients (protein is essential, so you can’t cut it out; just eat a reasonable amount). Fat is not magic, it’s just the safest source of calories. It is also very tasty and will help fill you up. So when you’re hungry, eat something fatty, such as buttered cheese, and try to get a bit more fat at your next meal.
. But it is how I usually start when someone I meet asks me how to do it. That really is the basics to keto. Replace carbs with fat. It won’t harm you. You will be going in the right direction. You can improve on the rest of it as you learn.