A Ketogenic Diet, as generally misunderstood by the lay reader, is a diet very low in carbohydrates and very high in dietary fat. That is, the fat in that Ketogenic Diet is taken by mouth. It is the fat you eat. But if you want to lose weight, you do not want to eat a Ketogenic diet very high in dietary fat. If you want to lose weight, you want the fat that your body burns to be the fat on your body that it has stored there for the purpose.
At the cellular level, the body doesn’t care where the fat comes from. So, while you’re hormonally in a “fat-burner” state (by eating a diet very low in carbohydrates), your body will burn the few carbs you ate first and then the fat you ate. 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 to maintain energy balance, it won’t. And you have defeated your purpose. You need to be careful not to OVEREAT fat, because you want to burn BODY fat.
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 the fat component is sourced. It is sourced in the liver where your metabolism breaks down the triglycerides (fat) you’ve stored instead of the triglycerides (fat) you ate. It’s a little harder to calculate, but the physiology is the same. The difference is that the macronutrient ratios of the “food” you use for energy are not measured where it is “taken by mouth” but where your body takes them up for energy – in the bloodstream.
Most nutrients from food you eat are absorbed into the bloodstream from where they are digested in the small intestine. From there they circulate until they are taken up by your cells. When you eat Very Low Carb, and your hormonal state has switched from sugar-burner (glucose-based) to fat-burner (fatty-acid based), your body will process the foods you ate and then, to maintain energy balance (homeostasis), it will break down your 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 will do this so long as you eat Very Low Carb and remain in the fat-burner state.
Your metabolism will NOT slow down. Your metabolism will continue to run at full speed because you are not being “starved” for lack of “food.” Your body has supplied the energy it needed from the “food” 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 fat eaten and stored fat. And YOU will determine the eaten/stored fat ratio by how much fat you eat.
Let’s do an example: A certain, mostly sedentary man (me) needs say 2,400kcal/day to maintain his current 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 the balance 75% fat (by calories, not grams). That’s 30 carb grams (120kcal), 120 protein grams (480kcal) and 200 fat grams (1,800kcal) a day. That’s 2,400kcal total. 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 will not lose weight because he’s EATING too much fat.Now, envision this same man eating the same 30 carb grams (120kcal) and the same 120 protein grams (480kcal) and BUT JUST 100 GRAMS OF FAT (900KCAL). His “diet,” i.e. what he has taken 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 because it is being fed with body fat, 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 taken up and used – the macronutrient components are unchanged. Both are Very Low Carb and Very High Fat and protein is the same. He is Fat Adapted, but by mouth, he is not eating a Ketogenic diet. But, at the cellular level, he is Ketogenic. I hope I’ve cleared up that misunderstanding.