"Fat Factors", by Robin Marantz Henig. Posted by Andrew V. Uroskie.

This article is about the role of gut microbes and viruses in determining a person's weight. The researchers concluded every person's menu of microbes is different, therefore the way in which they use calories varies, as well.

"A diet has a certain amount of absolute energy," [Jeffrey Gordon] said. "But the amount that can be extracted from that diet may vary between individuals -- not in a huge way, but if the energy balance is affected by just a few calories a day, over time that can make a big difference in body weight."

It is a long but very fascinating article that provides insight into the complexity of obesity and its causes.