[idle_zealot]

Of course not 100% of people are obese. Individual susceptibility varies, and as you mention could well be influenced by how the environment or common diets impacts the body, and further by how those changes in the body impact the mind. That said, its not really surprising that a decent portion of the population crave food rich in starches, fat, refined sugar, and salt. On an evolutionary timescale these nutrients have been scarse, so desiring them was advantageous. At the same time, problems from overconsumption were likely vanishingly rare, so there was no pressure to develope countermeasures like decreases appetite in responce to long-term abundance. In many ways our bodies and minds are not adapted for modern life, and this is a distinct problem from our inadvertent mass-poisoning ourselves.