Escrevi o texto abaixo como resposta a um blog de um médico que respeito muito, mas cuja opinião sobre dieta e obesidade representa exatamente o motivo pelo qual resolvi criar este blog. O texto original encontra-se aqui: http://theness.com/neurologicablog/index.php/how-to-lose-weight-eat-less-exercise-more/
A resposta (que traduzirei em breve) jamais foi publicada no blog acima. Assim, resolvi colocá-la aqui, já que acabou virando um bom resumo da minha opinião. Segue abaixo o meu texto:
I have had (and repeated) the exact same opinion you have expressed until a year ago. After trying a low carb diet and having an unbelievable success with it (lost 15 Kg of fat in 3 months without hunger and kept it thatway), I have been thinking and reading a lot on the subject.
First of all, nobody is trying to prove the first law of thermodynamics wrong. It just happens that this law has no cause and effect built into it. If you decrease your mass, you necessarily expend more calories than you take in. If you increase your mass, the opposite will be true. But this says NOTHING about the cause of this increase or decrease. It is a necessary condition, but it is meaningless. Everyone agrees that if you have a condition (like untreated diabetes) that increases the production of urine, it will also make you thirsty. By the same token, if you drink a lot of water (for whatever reason), you will urinate a lot. But this says NOTHING about cause. If a person urinates 5 liters a day, this may be because he or she has uncontrolled diabetes, or has diabetes insipidus (a completelly differente cause), or it could be that the person intentionally ingests a lot of water. Water in, water out, right? If you don't care about cause, what is to prevent you to treat diabetes by restricting water intake? It will decrease urine production, and you can then write about "the THIRST problem" (as opposed to the "hunger problem" of diets). The best analogy I know is the growing child (it could be the growing anything). For a boy to grow, he HAS to eat more calories than he expends. That's a truism. However, no one would argue that the boy grows BECAUSE he eats a lot. He eats a lot BECAUSE he is growing. The first law of thermodynamics is as valid here as it is valid everywhere. However, again, it says NOTHING about causality. The boy grows BECAUSE he has a hormone (GH) that directs his body to do so. And, in order to mantain energy (and mass) conservation, he NEEDS to eat more to compensate. Now, why would (human) fat tissue be the only tissue that is not controlled by hormones, but acts as a passive deposit of excess calories?
You cannot treat food and calories as if people are simple calorimeters that incinerate food in order to generate heat. Different foods have different endocrine actions, and this is crucial. Let's look at another example, type I diabetes. In this disease, the person makes no insulin. Of course, that means an impaired glucose metabolism. But this disease highlights another important function of insulin: fat storage. Before the discovery and clinical use of insulin, type 1 diabetics became emaciated as a result of accelerated fat breakdown. Fat storage requires insulin, and lack of insulin leads adipocytes to release fat into circulation. Physicians know that what usually kills an untreated type I diabetic is not so much the hyperosmolar coma due to very high sugar levels, but the metabolic acidosis due to massive amounts of fat being dumped into the bloodstream because of an absolute lack of insulin.
So, are all calories equal? In a calorimeter, sure. In a human body, well, 4 Kcal will still be 4 Kcal weather it is from fat, protein or carbohydrates, but they have different ENDOCRINE consequences and, hence, the ENERGY PARTITIONING can be quite different. Carbohydrates increases insulin and, as every biochemestry 101 student knows, this partitions calories towards storage (insulin is a storage hormone). In contrast, by avoiding carbohydrates and thus keeping insulin levels down, you end up having more lipolysis. Now your hunger decreases, because you are burning more of your own fat as energy. The end result is you eat less. But you eat less BECAUSE you are loosing weight, you are not loosing weight because you are eating less. This is no semantic trick. This is a huge difference. It means loosing weight by deliberately starving yourself versus doing it without hunger. In both cases, you eat less, so I agree with you that calories in, calories out, applies here, but this is concept is incredibly obvious and, at the same time, useless.
Having said that, my interpretation of the literature is pretty different. All prospective randomized comparisons of low carb diets consistently show greater weight loss and better cardiovascular markers when compared to low-fat diets. And those of us that have the clinical experience (I have been applying this to my patients for a year now) see a huge difference in terms of lack of hunger and compliance with a properly formulated low carb diet.
There are many other aspects that I could write about (satiety of proteins and fats, insulin resistance, leptin, etc.) in which different macronutrient ratios will have completely different implications in spite of having the same total calories in a diet. But I hope I made a point that calling a dieting strategy that has been around since the 19th century a "fad" is not the best approach. Nothing in biology makes sense outside of evolution theory. And we have good evolutionary reasons to suppose that (most) humans are not genetically adapted to having very high insulin levels 24/7 due to foods that weren't around when we evolved