[nscalf]

Well this is just wrong. First off, there is no evidence that it will be impossible for medical science to eventually solve most aging related illness, and mitigate most diseases. There is no practical reason to assume that trying to increase lifespan is a fools errand. Medical advancements look like big breakthroughs followed by decades of incremental improvements. Right now, it's starting to look like AI can increase the rate of breakthroughs and tighten the incremental improvement periods, so an extra 5 years of life may end up being enough to benefit from substantial medical progress.

Second, obesity isn't caused by the availability of food. Most well developed countries have an essentially infinite amount of food for any given individual, and most individuals do not stop eating because they lack the resources to access more food. So why isn't every individual in these society with these resources massively obese? Because there are a number of psychological, chemical, and biological reasons for obesity. Largely, the cause for obesity comes in the form of appetite suppression vs satiation. There are many chemicals like PFAS which decreases satiety, increasing the calories you intake.

Just like how removing heavy metals from drinking water and increases in food availability increased the general quality of life for all affected people, decreasing the amount of chemicals affecting satiety in the general environment could have massive impacts for societies that are impacted.

In short, if your baseline hunger is lower, you won't get fat.