Nobody ever reads this blog, which is fine by me. I have occasionally written some articles about diet, and this is another one. I have deliberately chosen a provocative title to make this interesting.
Obviously you can't eat vast quantities of food and expect to lose weight. I am just criticizing those people who log everything into apps to figure out the calories and try to maintain a 200 calorie (or whatever) deficit per day, and then try to lose1 lb a week.
Not all calories are created equal. How are calories determined? Basically, food scientists use a calorimeter, burn the food item to ashes, and then determine how much energy is released. But the body doesn't use energy this way.
Read this article: https://www.ruled.me/too-much-protein-bad-for-ketosis/ which does a good job of explaining it.
Basically, think of eating and digesting food as a chemical process. Your body needs a certain number of calories each day to survive (but that number is less than you think, and you don't have to consume food every day to meet that number). Let's say that say that number is 800 calories. Your digestive system will turn all food you eat either into blood sugar or fat. (Any carbs will be turned into sugar). An excess of blood sugar will trigger insulin. An excess of fat will trigger glucagon. "Insulin decreases ketone production while glucagon stimulates it."
So the ideal diet (for someone trying to lose weight via ketosis) is an almost unlimited amount of fat, limited protein, and almost no carbs. How much protein should a person eat? The rule of thumb is 0.8 grams of protein per kilograms of body weight per day, which is 0.36 grams per pound. So a 200 lb man would need 72 grams of protein per day. One 5 ounce can of tuna has 26 grams. Turkey breast has 5g per ounce. A quarter pound (4 oz) hamburger has 31g of protein So that is 3 cans of tuna per day or 14 ounces of turkey or 9 ounces of hamburger.
What happens to the excess protein? Read the article above. There isn't a simple answer to this. Excess protein generally doesn't spike insulin in the same way that carbs do, but it will increase it slightly. It depends on the insulin sensitivity of the person. If you are insulin resistant, like a diabetic or obese person, then you need much insulin. If you are insulin sensitive, then you don't need as much insulin. The excess protein is mostly stored as glycogen, but at some point, if you eat way too much, it is treated just like a carb.
What happens if you eat too many carbs? They are first stored as glycogen at a 1 to 4 or 1 to 5 ratio. So 1/2 lb of excess carbs can cause (temporary) weight gain of 2 lbs.
What happens if you eat too much fat? Generally not a problem, however you could get fatty liver disease if you have a damaged liver (from drinking too much alcohol).
So back to the original question - if I am saying CICO doesn't work, then what does work? Well, to figure out the exact formula, you would need to know your maintenance calories and you would need your insulin sensitivity number. And you would need to know how healthy your liver is.
So I would scrap CICO. Instead be very strict about carbs and rate yourself on a pass/fail basis. (If you eat more than a trivial amount of carbs you fail). Measure grams of protein instead. Since there are 4 calories per gram of protein, aim for about 300 calories (4*72) per day from protein. And totally ignore fat, except there should be an upper limit, of maybe 150 grams of fat per day. One ounce of butter has 12g of fat, so don't eat more than about 12 ounces per day. (It is really hard to eat that much fat without carbs).
So there you go. The only thing you should be measuring is protein. Of course, if you insist you can lose weight while eating carbs, then more power to you.
Disclaimer: I am not a registered dietician and this is not medical advice.