It's an old axe that you are what you eat, but a growing body of evidence suggests that, in terms of our gut bacteria, it's really true. Recent research shows that the standard 'Western' diet high in animal fat, sugars, and refined carbohydrates fundamentally alters the bacterial ecosystem in our intestines. The bacteria that thrive in the house that McDonald's built are not only associated with obesity, but may actually excrete waste compounds that cause obesity.
So, what's an overweight person to do? If they've still got healthy bacteria lurking around, a switch to whole grains, fruits and vegetables will do the trick. The truly desperate – those who find losing weight to be nigh impossible – they can try a fecal transplant from a skinny person. Yes, it's exactly what it sounds like. However, as the Western-style diet spreads, we may be experiencing a hidden mass extinction. French fries and candy bars are destroying the habitat of friendly bacteria that evolved with humans for millions of years.
Enterprising 'fecoprospectors' are combing rural and tribal populations to catalog and preserve healthy, natural gut biomes. In some cases, scientists have even used mummified poo to reconstruct the bacteria that co-existed with extinct human populations. Perhaps soon we'll feel the need to set up 'poop reservations' and mandate that the inhabitants stick to their old-fashioned ways. Or, of course, we can all eat more plants and unprocessed foods, but that seems a little too simple to work.