To quote @PaulL:
There are three macronutrients: fatty acids, protein, and carbohydrate. Carbohydrate stimulates insulin production, and insulin is the hormone that causes fat to be stored in the fat cells (adipose tissue). At the level of carbohydrate consumption recommended by the U.S. government, most people’s bodies produce insulin at a very high rate, forcing most ot the carbohydrate to be stored as fatty acids in the adipose tissue. To mobilize excess stored fat for metabolism, therefore, we have to find some way of lowering our insulin level. The good news, however, is that the body’s daily requirement for carbohydrate is 0 (zero) grams.
Protein stimulates insulin production, but at about half the rate of carbohydrate. Since we absolutely require protein in our diet every day, we need to eat enough protein to avoid malnutrition while avoiding eating too much (for one thing, that way lies ammonia toxicity). For most people, a good range to eat is 0.8 to 1.0 grams of protein per kilogram of lean body mass each day.
Fat hardly stimulates insulin production at all, so to give our bodies the calories they need, it’s the only really safe macronutrient to eat. The reason we say “eat fat to satiety” is that doing so allows the body to tell us how much it needs; for most people, a few weeks of eating a well-formulated ketogenic diet is enough to restore satiety signaling, a sensation by which we lose interest in eating for a while. So there is no need to count calories, because the body decides what it needs, and all we have to do is eat fat until we stop being hungry. For most people entering ketosis, eating fat to satiety leads them to spontaneously limit their calories to around 1500 or so a day. But there are verified records of study participants eating far more than this while still losing excess fat, so don’t worry about how much you’re eating. When given an abundance of calories the body ramps up the basal metabolic rate and even finds ways of wasting calories, whereas limiting calories runs the risk of giving the body the impression there’s a famine on, and it needs to conserve energy at all costs.
There are two hypothesese of nutrition, one of which is about energy expenditure, and which we on these forums ridicule as CICO (Calories In, Calories Out). The other hypothesis takes into account hormonal regulation of food partititioning. Keto is based on the latter theory.
The problem with the energy-expenditure hypothesis is that you need to calculate your energy intake and expenditure to within about 20 (kilo)calories a day, if you don’t want to gain (or lose) weight, and this is impossible. To calculate your energy expenditure you need to know, among other things, your basal metabolic rate, which varies according to your food intake. How are you going to figure that? You also need a highly accurate assement of the caloric value of your food, which is also practically impossible to attain.
The hormonal-regulation hypothesis takes into account known science about the effect of carbohydrate on insulin secretion and the effect of serum insulin levels on whether fat is stored or metabolized. There are other hormones involved, but insulin is the key factor, and the effect of sustained high serum insulin levels has been determined to be the cause of metabolic disease (diabetes, cardiovascular disease, obesity, high blood pressure, stroke, gout, dental cavities, Alzheimer’s disease, and certain types of cancer). By allowing insulin levels to drop, a low-carbohydrate, high-fat diet has been shown to reverse metabolic disease, allow excess fat to be metabolized, and also switch the body from glucose as a main source of fuel to fatty acids and ketone bodies, particularly beta-hydroxybutyrate.
The key is to keep carbohydrate intake low enough to allow ketosis and fat-adaptation to take place, and to keep fat intake high enough to provide adequate energy to the body. In the presence of insulin, the muscles burn glucose and the fat cells store fat; in its absence, the muscles burn fat and the fat cells are free to release fat for them to burn. If you eat fat to satiety, your body will regulate your appetite to ensure that it has abundant energy, whether that energy comes from your diet or from your store of excess fat. Fat is highly satiating, so people generally find themselves stopping eating at a caloric level, whatever that happens to be, that allows the body to consume its excess fat store. The point is not to count calories, but to allow the body to set its own level. As Dr. Eric Bergman likes to say, “Calories do count—but you shouldn’t count them.”
The business about not eating too few calories comes from the fact that, in the presence of inadequate food intake, the body goes into starvation mode, cutting back on energy expenditures and reducing the basal metabolic rate. By contrast, in the presence of abundant food intake, the body ramps up the metabolic rate and at low insulin levels can even waste energy by burning excess fat for heat. Paradoxically, it’s better to eat nothing than to restrict calories on purpose.
Whlle there are people who have documented eating 3,000 or 5,000 calories a day on a ketogenic diet and still lost weight, I’m not sure it is possible for everyone. Dr. Phinney has found that the usual pattern is that when people with excess fat stores eat fat to satiety, they naturally limit themselves to around 1500 calories, the balance of their energy requirement coming from stored fat. As their excess fat deposits are eliminated, eating fat to satiety automatically raises their caloric intake to compensate, until they reach the point where all their daily energy needs are supplied from their food intake.
So the hormonal-regulation hypothesis says that the nature of the foods we eat has an effect on our body and determines whether each food gets metabolized or turned into fat and stored. The caloric value of each food is of secondary importance to the body’s decision whether to store or metabolize it. The energy-expenditure hypothesis, on the other hand, claims that our total caloric intake is all that matters, regardless of whether those calories take the form of sugar or other carbohydrate, protein, or fat. As simple and obvious as the energy-expenditure hypothesis appears at first glance, the hormonal-regulation hypothesis has far more science to back it up. From my own experience I can testify that taking this science into account in my way of eating has eliminated my metabolic problems and allowed me to lose sixty pounds, without ever going hungry or counting a single calorie.
