When cows are fed with corn instead of grass, they produce more of the harmful toxin, e. coli.  This is caused by improper breakdown of the starches, since cattle are designed by nature to chomp grass not leftover grains.  Of course, when they do eat a primarily grain fed diet, their flesh is better marbled with fat...so it appears more desirable to the decadent meat eaters. 

(I wonder if part of the reason unhealthy meat appeals to us is that somewhere deep inside our primitive selves remember that we aren't supposed to destroy healthy, strong, vital animals...we are supposed to strengthen other species by taking down the weak and preying on the less healthy.) 

I also wonder if the same is true for human diet?  Maybe not so much over abundance of E Coli (we might notice that?) but other inhospitable organisms.  Like the kinds that may (or may not) be linked to Crohns disease, and other Inflammatory Bowel Disease.  Or simply an overgrowth of bad bacteria that leads to an epidemic of IBS?

Of course, I'm not a doctor.  The two probably aren't related.  A professional would surely tell you...it's just stress.  Maybe what we really should ask is who's stress matters most...ours, or that of the animals we eat?