Air pollution seems unlikely as it's been falling for decades, and America has much lower levels than Europe. Microplastics are a perennial boogey man, and probably a genuine ecological issue, but there has no been mountains of studies done and documented health effects are virtually non-existent. Livestock and slaughterhouse conditions are certainly not good from an animal welfare perspective, but we've had similar practices for 100+ years and obesity wasn't a major issue in 1960. Pesticides in food products have been substantially reduced since the EPA changed guidelines in the 1990s, and yet obesity has exploded since then.