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There are two dominant theories as to why Westerners have gotten increasingly obese in the last fifty years. One is that we're eating too many carbs and carbs make us fat. Another is that our primitive appetite \u2014 which is wired to gorge on calorically dense foods as a survival mechanism \u2014 is misaligned with a modern landscape in which food is available in an overabundance.\n\nMy guest today says that there's too much evidence which contradicts these theories for them to completely explain the problem of weight gain, and forwards a different and quite surprising theory as to what may be going on instead.