A few probable culprits:

- plastics / microplastics

- processed food / ultra processed food

- processing / conserving chemicals

- pesticides

- GMOs

- And last, but certainly not least, a combination of all the above, at concentrations well below any "proven" toxicity level

Yep. The food, soil, and water systems are now and probably forever more riddled with plastics, heavy metals, and industrial agro chemicals. Plastic pollution (being a massive diversity of different petrochemicals) are probably the largest growing issue that would explain the US increase.

However, there is one more culprit that is have recently been getting educated on. Blue light pollution.

I’ve been learning how the more we disrupt our circadian rhythm with screens and artificial light, especially at night, we massively disrupt our natural hormone cycles (master hormone leptin for example). This makes it impossible for adults past a certain age to lose any weight (regardless of diet and exercise), exacerbating the already growing obesity problem.