"many modern diets provide very little good food for microbes"
... thought for food... and why you should NOT eat highly processed foods... here.
"Empirical evidence has shown that rising obesity rates closely parallel the increased consumption of processed foods (PF) consumption in USA. Differences in postprandial thermogenic responses to a whole-food (WF) meal vs. a PF meal may be a key factor in explaining obesity trends, but currently there is limited research exploring this potential link."
In other words... if you eat processed foods you WILL get fat because your body absorbs more calories and you are not absorbing the microbes necessary to adapt to this...