Maybe? I don't think we all know this. And some research, especially into people with unusual metabolism (but not necessarily known metabolic disorders) indicates that even with these restrictions, they need to operate at a significant calorie deficit simply to maintain a healthy weight. [1]

It might be that they are already exposed to enough processed food and pesticides that simply getting those things out of their diet is not sufficient, but I think it's clear that there's more going on here than a simple answer.

And, I think, most damningly, there are many people who maintain a healthy weight with no active efforts to maintain that weight, including a lack of exercise and consumption of processed food. It might be that a significant fraction of people are resistant to this effect or might just not enjoy the taste of processed food so naturally gain the benefits of avoidance.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989512/