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Dobbiamo ripensare le cause dell’obesità?

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Il giornalista scientifico Gary Taubes, uno dei 17 autori dell’articolo The carbohydrate-insulin model: a physiological perspective on the obesity pandemic” pubblicato su The American Journal of Clinical Nutrition (open access), ha scritto un articolo per STAT  in cui spiega le ragioni che lo hanno portato a mettere in dubbio il paradigma generalmente accettato per spiegare l’obesità, ovvero quello dell’energy imbalance (lo squilibrio tra apporto e consumo di calorie) e a diferendere il carbohydrate-insulin model. Ne parla anche SkyTG24.

By this ubiquitous thinking, obesity is an energy balance disorder: People get fat because they take in more calories than they expend. They stay lean when they don’t.

This is the central dogma of obesity science. Virtually all obesity research is interpreted in the context of this balance principle; all related public health discussions, not just on obesity but on all the common chronic diseases that associate with it, as well as the very nature of a healthy diet, rely fundamentally on its implications.

L’autore ripercorre la storia della ricerca sull’obesità e parla della nascita di questo paradigma. Nel 1930, Louis Newburg, uno dei primi ricercatori che si occupò di obesità, scriveva:

“The medical profession in general believes that there are two kinds of obese persons, those who have become fat because they overeat or under-exercise; and those composing a second group whose adiposity is not closely related to diet, but is caused by an endocrine or constitutional disorder.”

Questa affermazione porta a concludere che alcune persone siano predisposte ad accumulare grasso. È però innegabile che l’ambiente abbia un ruolo fondamentale.

The undeniable evidence is the enormous increase in the prevalence of obesity worldwide. In the U.S., 12% of Americans lived with obesity 60 years ago; more than 40% do today. Something has changed in the environment — in diets or lifestyles — to trigger such a dramatic rise in the prevalence of obesity. But is it nature or nurture that the environment triggers, behavior or physiology, minds or bodies?

Nel 1929, Newburg rispose a questa domanda in seguito ai suoi esperimenti sulla restizione calorica in pazienti obesi:

(…) Newburgh claimed to have established experimentally and definitively the primacy of overeating as its manifest cause.

When the Los Angeles Times reported on Newburgh’s work in 1932, the headline put it in appropriately blunt perspective: “Just Gluttony Causes Obesity. Michigan Professor Strips Defense of Portly.”

Da quel momento in poi la domanda per ogni scienziato è stata “perchè gli obesi mangiano troppo?” e non “perchè gli obesi accumulano troppo grasso?”. 

Had physicians in the 1930s thought to conceive of obesity as a fat accumulation disorder — an assumption-free definition of the problem — rather than as an energy-balance problem, they might have studied the physiological mechanisms that regulate fat storage.

Immagine da Pixabay.

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