Why do rats get fat?

(versión en español: pinchar aquí)

The Calories In Calories Out (CICO) theory should be valid for all animals (why wouldn’t it? It’s all about calories, not physiology, right?). I read about a study in rats in an article titled “Increasing Adiposity. Consequence or Cause of Overeating?“:

Rats fed high vs low glycemic index diets developed hyperinsulinemia, increased expression of fatty acid synthase in fat tissue, and greater incorporation of glucose into lipids— metabolic abnormalities that predispose to excessive fat deposition. When the high glycemic index animals were food-restricted to prevent excessive weight gain, they still gained substantially more fat (70%) than the low glycemic index animals and also exhibited adverse changes in cardiovascular disease risk factors.

This combination of increased adiposity despite reduced energy intake cannot be explained by the calorie-centric view of obesity but may be understood by the alternative model. (see)

Even when food-restricted, those rats gained more fat, because they ate a high-glycemic index diet.

From that result we can only conclude that the CICO theory is wrong. About that, the authors of the article say that “feeding studies demonstrate that changes in energy balance produce biological adaptations that antagonize ongoing weight loss or gain”. In other words you are not going to lose weight in the long term with a hypocaloric diet, i.e. following the CICO dogma, because your body adapts itself to the new calorie intake. Moreover, they warn us that conventional calorie-restricted diets “could exacerbate the underlying metabolic dysfunction by further limiting metabolic fuel availability, lowering energy expenditure, and increasing hunger“. Hypocaloric diets don’t stop the fattening process, quite the opposite. And the authors provide us with a schematic graph showing the differences between the prevailing model of obesity’s causes, and their own view:

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I think model A is just nonsense: another lie from the people that made us fat. Model B seems much better, doesn’t it? But in model B I don’t get the final step: how do increased energy intake and reduced energy expenditure cause obesity? I need a physiological mechanism and I can’t find one. I have asked this question before in this blog, but I still have no answer:

How does an adipocyte (fat cell) know we are eating too much and doing little exercise, so it can decide to store fat instead of releasing it?

Even the authors of the article say adipocytes store fat because of carbs, and changes in energy intake/expenditure are just a symptom, not a cause:

According to an alternative view, the metabolic effects of refined carbohydrate (consumed in greater amounts now than in the 1970s, with adoption of the low-fat diet) and other environmental factors cause the adipocyte to take in, store, and trap too many calories. Subsequently, energy expenditure declines and hunger increases.

It is not about calories: it is about physiology. I changed a little model B’s scheme so I can agree more with it:

Reading further:

 

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