If say every human on the planet had a diet of processed foods high in sugar, salt, fat, and oils. All the corn syrup goodness and mechanically separated filler meat . If every human on the planet had this diet, how would our digestive system and bodies adapt? Could we adapt and if so what would it's changes be in 1,000 or even 100,000 years?

Charles Darwin`s Theory of Evolution and Natural Selection may answer your question. It is good to be open-minded.

Note that our bodies adapt only within our own lifetime but that is not necessarily transferred to the next generation. What you may be thinking of is that whether in a population a pool of e.g. high cholesterol resistant people may persist while others die off.. The key point is whether that diet influences reproductive success. Typically issues associated with high fat, salt and sugar (I think it is better to specifically target these points as "processed" is a bit broad) manifest issues later in live (on average). So people may start dying in their 50s (to pull out a random number), but they will have had kids before that.

Note that our bodies adapt only within our own lifetime but that is not necessarily transferred to the next generation. What you may be thinking of is that whether in a population a pool of e.g. high cholesterol resistant people may persist while others die off.. The key point is whether that diet influences reproductive success. Typically issues associated with high fat, salt and sugar (I think it is better to specifically target these points as "processed" is a bit broad) manifest issues later in live (on average). So people may start dying in their 50s (to pull out a random number), but they will have had kids before that.

Doesn't obesity affect fertility and sex drive, though? So people may not (typically) be dropping dead before the age that they'd reproduce, but they may be somewhat less likely to have children than someone who metabolizes the crappy diet better. And even if the adverse health effects are more likely to show up later in life, that doesn't mean they never start early. Even a slight decrease in reproductive fitness will have some impact.

 

It's just that this probably won't be a particularly strong pressure, so any evolutionary changes resulting from it are likely to take quite a long time to manifest on a population level.

Wouldn't the environmental pressures of our diet being diabetes, high blood pressure, high cholesterol. Wouldn't we naturally select and adapt to these changes in our body over the course of multiple generations?

What is a "processed food"? Really any modification to food, whether it be grinding, cooking, etc is processing of some sort. Man hasn't ate "raw" food on a regular basis for a long long time.

I could see how this not having much effect on reproductive efficiency, thus not having enough environmental pressure for us to evolve.