Do NOT eat a Ketogenic Diet to lose weight! If you’re “normal” weight, or you have intractable epilepsy and will benefit from a very high dietary fat diet, then okay. Eat a high fat diet. But if you are overweight and want to burn body fat, you first need to get in a hormonal state conducive to fat burning – by eating Low Carb (LC). Or, if you have Insulin Resistance, eating Very Low Carb (VLC); then, while eating LC or VLC, and “enough” protein, you need to be careful not to over EAT fat because, you want to burn BODY fat.
A Ketogenic Diet, as defined here and elsewhere, is very high in dietary fat. Whatever else it is, the fat in the Ketogenic Diet is thus taken by mouth. But at the cellular level, the body doesn’t care where the fat comes from, and it has to do something with the fat you eat. So, while you’re hormonally in a “fat-burner” state, as your body digests the fat you eat, it’s going to burn what it needs and store what it doesn’t. And if it doesn’t need to burn your body fat, it keeps it in reserve, as it was intended to be. You have defeated your purpose.
So what does this do to the macronutrient ratios I have talked about for years? It doesn’t change the ratios. It just changes where they are sourced. Your biology hasn’t changed, just the way you (or I) pictured it. It’s a little harder to calculate, but the physiology is the same. The difference is that the macronutrient ratios are not measured where it is “taken by mouth” but where your body takes it up for energy – at the cellular level.
Most nutrients from food you eat are absorbed at the small intestine. From there they circulate in the blood or are held in the liver until needed. There are some exceptions: iodine is stored in breast tissue, lutein is stored in the macula of the eye, for example. When you eat VLC, and your hormonal state has transitioned from sugar-burner (glucose-based) to fat-burner, your body will first process all the foods you ate and then, to maintain energy balance (homeostasis), it will break down body fat (triglycerides) into fatty acids for fuel. Fatty acids will then circulate and mix with the other fuels in the blood until taken up wherever needed. It can do this, remember, only so long as you eat LC or VLC and remain in the fat-burner (vs. sugar-burner) state.
Your metabolism will NOT slow down and you will NOT excrete vitamins and minerals before they can be stored. Your metabolism will continue to run at full speed because you are not being “starved” by the absence of “food.” Your body has supplied the “food” it needed from the energy reserves it had stored.
So, in practical terms, what does this do to the macronutrient ratios, as traditionally applied to food ingested (taken by mouth)? The ratios don’t change. The carbs are exactly the same. The protein is exactly the same. Total fat is the same too, only it is divided between eaten fat and stored fat. And YOU will determine the fat ratio by how much fat you eat. To keep in energy balance, the remainder will be body fat that you burn.
Let’s do an example: A certain, mostly sedentary man (me) needs say 2,400kcal/day to maintain his “normal” weight. But, he’s overweight and wants to burn body fat, so he eats a diet with macronutrient ratios that gets his body in a hormonal state conducive to fat burning: 5% carbs. 20% protein and 75% fat. That’s 30 carb grams, 120 protein grams and 200 fat grams a day. If he eats this Ketogenic Diet (k/g ratio: 2.0), he will not be hungry. He will be fat-adapted and in ketosis, but he won’t lose weight. He’s EATING way too much fat.Now, envision this same man eating the same 30 carb grams and the same 120 protein grams and but just 100 grams of fat. His “diet,” i.e. what he has taken in by mouth, is now 1,500kcal/day, but because he is still eating Very Low Carb, he is still in a hormonal state conducive to fat-burning, and his body will have to break down 100 grams of body fat a day to maintain the 2,400kcal his body requires for energy balance. His metabolism runs full speed, he is not hungry, and he loses weight. His macronutrient ratios (by mouth) are now 8% carb, 32% protein and 60% fat (k/g ratio just 1.4), but it doesn’t matter. At the cellular level – where the energy is used – they are unchanged. Both are Very Low Carb. He is still fat adapted but, at K:G=1.4, he is not ketogenic.