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«There are no fattening nor slimming foods. What makes you fat are the calories you don’t burn, no matter the food they come from. Some foods are more caloric dense than others, and that is all.»
Let’s think, hypothetically, of two identical twins. Both of them eat the same amount of calories, but the contents of their diet is different, will they lose or weight always the same amount of weight? If we believe that for our body it is all a matter of calories, no matter the food they come from, we must answer «yes» to that question, right?
Young et al. compared 3 isoenergetic diet (1800 Calories/day), all 3 with the same amount of protein (115g), but different amounts of carbs (30g, 60g and 104g/day) and fat (136g, 122g and 103g).
After nine weeks of eating this way, those who followed the diet with 30g of carbs (diet C) had lost an average of 16.2Kg , while those who followed the diet with 104g of carbs (diet A) only lost 11.9Kg, a difference of more than four kilograms.
Remember that the 3 diets, A, B and C had the same caloric count: 1800 Calories/day. And the result is that the diet that produces a bigger weight loss is the one with more calories from fat and less carbs.
Moreover, in those subjects who followed diet C, 95% of the weight loss was from fat. But for those on diet A, the one with the more carbs, only 75% of the weight loss was related to fat. Diet composition does not only determine how much weight you lose, but also the quality of that weight loss.
If the only parameter that matters is the total amount of calories of the diet and not where do those calories come from, how can the results above be explained? There is no doubt that inferring from just the caloric contents of a food, if it is going to make us fat or not, is deadly wrong. Calories measure the energy stored in the foods, the heat you can extract from them if you burn them in an oven.
«One calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius»
Is the way our body works even remotely similar to the way a water heater works? We, human beings, are much more complex than a water heater and the foods we eat induce in our bodies extreamly complex physical and chemical reactions. Not all foods contain the same metabolizable energy, not all of them induce the same changes in our basal energy expenditure, not all of them change our hormones to the same degree.
What is more fattening, 100 Calories of butter or 100 Calories of bread?
If we answer that «the are equally fattening» we are ignoring all the scientific evidence and we are accepting the dogma that says that all calories are equal, no matter their source. Answering that «the are equally fattening» implies the assumption that a system as complex as the human body works exactly in the same way as an oven or a water heater. And the problem here is that that theory is wrong over and over again. May be we don’t fully understand why specific foods are more fattening than others (held constant the caloric content), but we can’t deny that fact, specially when the «a calorie is a calorie» dogma has clearly not helped people to stay lean. This dogma is not just wrong: until it is not buried, people can’t be told how to eat in order to stay healthy.