Eating well makes you happy. We can argue endlessly about what defines "well", from ethically-sourced local legumes to deep-fried industrial bacon.

It's the sort of argument that draws in both politics and health, and is irreducible: There aren't many simple answers to how to eat well, especially if you come from the perspective that there are serious problems with the food system. What is incontestable is that food affects our emotional state. It's an aphorism that makes Brillat-Savarin's observation (and slogan for Iron Chef) "Tell me what you eat, and I will tell you what you are" seem obvious. But how? Why is food particularly memorable beyond the multitude of sensations that it invokes? Beyond satiating hunger, the effects of food on our body and our sense of self are complex and contested.

Interesting research on the "gut-brain axis" seems to support that what you eat also begins to form who you are. John Cryan, a neuroscientist at University College Cork in Ireland, has completed a short study on rats that seems to suggest an effect of probiotic and generally benign bacteria to change minds. From the American Association for the Advancement of Science:

One recent study suggested that even benign bacteria can alter the brain and behaviour, but until now there has been very little work in this area, Cryan says. To further investigate the mind-altering potential of benign bacteria, Cryan and colleagues at McMaster University in Canada fed mice a broth containing a benign bacterium, Lactobacillus rhamnosus. The scientists chose this particular bug partly because they had a handy supply and also because related Lactobacillus bacteria are a major ingredient of probiotic supplements and very little is known about their potential side effects, Cryan says.

In this case, the side effects appeared to be beneficial. Mice whose diets were supplemented with L. rhamnosus for six weeks exhibited fewer signs of stress and anxiety in standard lab tests, Cryan and colleagues report online today in the Proceedings of the National Academy of Sciences [PNAS]. For example, the rodents spent more time exploring narrow elevated walkways and wide-open spaces, which are scary to rodents, and they exhibited a smaller spike in stress hormone levels when the researchers put them in water. "This was really exciting because it tells us the animals are more chilled out and don't mount the same stress response," Cryan says.

Maybe rats are more chilled out when their food tastes different. It's probably going to ramp up the claims of probiotic foods, which are best approached with a huge degree of skepticism: The ways in which food makes us happy is a very human endeavour.