I was also dubious of the claim that "processed" foods are less healthy, but there does seem to be some evidence to support the claim at least along one vector:
> Processing may affect the natural resistant starch content of foods. [...] Whole grain wheat may contain as high as 14% resistant starch, while milled wheat flour may contain only 2%.
> The fermentation of resistant starch produces more butyrate than other types of dietary fibers.
> Butyrates are important as food for cells lining the mammalian colon (colonocytes). [...] Butyrate is extremely essential to host immune homeostasis.
Basically, resistant starch is extremely important to the health of your colon, and fairly important to your health in general. From what I hear, colon cancer is not terribly fun. Since processing greatly reduces the resistant starch content of certain goods it seems reasonable to claim that "processing" makes some foods less healthy.
Though like all things there is a lot of subtly here; I wouldn't be surprised if plant based burgers end up healthier on the whole despite the processing when compared to regular meat. But they are unlikely to be healthier than the equivalent in unprocessed veggies.
> Basically, resistant starch is extremely important to the health of your colon, and fairly important to your health in general.
So if you eat exclusively processed grains, you don't have the resistant starch. Meanwhile, red meat is linked with actually causing colon cancer, not just failure to prevent it.
In a nation where most people have an extreme caloric surplus, "processing", aka "cooking" increases the caloric intake of diners. Processing usually removes fiber also.
A lot of processing does entail removing fiber and other nutritional content. That's why I just eat normal vegetables, not lab atrocities created at McDonald's.
