There are clear and unan­i­mous fig­ures that obe­si­ty has increased over time, espe­cial­ly in rich nations like the Unit­ed States. On aver­age peo­ple today weigh more and have high­er body fat per­cent­ages than their recent ances­tors at sim­i­lar ages. But why is that the case?

One wide­spread assump­tion is the palata­bil­i­ty the­o­ry. It posits that the pri­ma­ry cause is an increase in reward sig­nals in the mod­ern envi­ron­ment from processed food, medi­at­ed by the moti­va­tion sys­tem in the brain, caus­ing us to overeat.

This the­o­ry was out­lined by Stephan J. Guyenet in his book The Hun­gry Brain, pro­vid­ing his own spec­u­la­tion, point­ing to genet­ics, and not only because of this fact it has been wide­ly dis­cussed late­ly. But what exact­ly are we faced with? A sci­en­tif­i­cal­ly found­ed con­cept? Or just a the­o­ry that let Guyenet take a supe­ri­or per­spec­tive and say that oth­er peo­ple can’t help themselves?

Matthew Bar­nett intends to clar­i­fy the core claims of the palata­bil­i­ty the­o­ry in an arti­cle pub­lished on Less­Wrong, because «there are many ways to be con­fused about what the the­o­ry is actu­al­ly claim­ing, and indeed, I think many peo­ple are at present con­fused about it. There­fore, I’m going to go through the main parts of the the­o­ry, step by step, in the hopes that this clears up some confusion.»

It’s a detailed, but nev­er ver­bose analy­sis that is worth read­ing and think­ing about. And Bar­nett makes an unequiv­o­cal judg­ment, adding one wish: «My hope is that, if you dis­agree, you can be more pre­cise in your dis­agree­ment by object­ing to one of the core claims of the the­o­ry that I have now provided.»