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Yogurt makes you … shinier

At least if you’re a mouse. Research published this month found that mice fed yogurt were slimmer, sleeker and shinier than those that didn’t.

The male yogurt-eating mice also had larger testicles. (The junk-food eating mice had smaller testicles.) Female mice weren’t left out: they were smooth and shiny too, and had larger healthier litters.

In other words, eating yogurt made mice more attractive and more fertile, and presumably healthier. The researchers don’t know why, but they suspect it might have to do with the live bacterial cultures in the yogurt.

By the numbers, the human body is mostly bacteria: about one trillion human cells, and about ten trillion bacteria. (I don’t know the numbers for mice, but they’re probably similar.) We don’t even know what most of them are, though scientists think there are around 500 different species.

Many of those bacteria live in the digestive system, having colonized the infant during birth or shortly after. They help to digest the things we eat, release vitamins, help to keep out disease-causing bacteria: all sorts of useful things. The humans studied so far fall into one of three enterotypes, each of which has similar distinctive gut assemblages (even though they eat similar diets).

Nobody knows exactly what that means yet, but one possibility is that different enterotypes are more efficient at digesting particular foods. They may also be more or less effective at providing vitamins to their host. The abundances of different species change in response to diet, but mostly within certain limits. Gut flora have been linked to obesity, suggesting that bacteria may affect metabolism or efficiency of digestion. Having (or eating) the right bacteria might also be related to longevity.

When gut bacterial assemblages decline or get unbalanced, often as a result of taking antibiotics to treat some other condition, all sorts of problems can occur. One particularly nasty invader is Clostridium difficile, a bacterium that can cause persistent diarrhea and may become debilitating or life-threatening. Even C. diff, as it’s not-so-fondly known, is vulnerable to a diverse and balanced set of gut bacterial: a fecal transplant from a healthy individual is an effective cure.

Gut bacteria could have global environmental implications too: scientists are looking for ways to modify ruminal bacteria in cattle so that they eliminate less methane, a powerful greenhouse gas.

This stuff has all kinds of science-fictional implications. What about modifying the gut flora of planetary colonists to help them digest new foods, or to produce vitamins that they no longer get from their diet? Or superfoods that promote health or shininess or fertility? Such superfoods could be proprietary, or addictive. What happens if people try to culture them at home? Making your own yogurt is easy, and using a commercial yogurt as the starter ensures that you have the same culture. For the probiotics to contribute to the gut flora, they have to be alive.