4 P52290 16. So we can retrain our brains to desire different foods. 17. While the brain clearly has a huge influence over what we eat, the influence of gut bacteria might be surprisingly large, too, and they can even affect our minds. 18. Joe Alcock at the University of New Mexico in Albuquerque and his colleagues published a review of research on the microbiome and came to an intriguing conclusion – gut microbes don’t just flourish on certain diets, they may also control our food cravings and preferences to serve their own purposes. 19. There are several ways they could do this. Animals’ gut flora has been shown to affect their taste receptors, which changes their food preferences. And many gut microbes can produce proteins that mimic gut hormones. Alcock’s team even thinks that changes in food preferences that people experience after bariatric surgery might be down to changes in gut microbes, not hormones. 20. That means interventions like probiotics, which help to change the composition of the microbiome, might be useful tools in regulating food cravings. And it suggests a varied diet would make it harder for any one type to flourish and exert control. 21. Because the faecal and oral microbiomes of families under the same roof are more similar than people who don’t live together, the idea that food cravings are influenced by gut bacteria also raises the intriguing possibility that through the spread of these microbes, cravings could even be contagious. Of course, this similarity could be because the members of a household have the same diet. But it might also be that gut bacteria are spread person to person. We already know people are much more likely to become obese if they have a friend who is obese, leading some to speculate that the effect is not down to social contagion, but the spread of microbes. 22. More needs to be done to work out how strong all these effects are, but this new appreciation for the hidden forces influencing our perception of food has wide-reaching implications. Goldstone even wonders whether tapping into the connection between the hunger and reward pathways could alter appetites of a different kind. Animal studies have already shown that ghrelin increases intake of alcohol, nicotine and other drugs, while “fullness” hormones reduce intake. 23. He suspects the same is true for humans. “We’ve shown that your nutritional state modifies the way the brain responds not just to food but also to winning money, and to stress,” he says. “That’s because the same reward circuitry is involved. There’s evidence that gut hormones modify not only reward and consumption of food but also any drug of abuse – such as nicotine, cocaine, alcohol,” he says. They are now beginning a large study. 24. At the very least, all this suggests that expecting people to rely purely on willpower to control what they eat, especially if they are obese, is misguided. “There’s a cabal of obesity researchers that have turned up their hands and said the only thing you can do is rely on willpower,” says Roberts, “I don’t think it’s worked for the last 30 years and it’s not going to work next year either. Which is why we’re trying to do it in a different way.”