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Experiments in mice show that gut bacteria, combined with a high-fat diet, can lead to heart disease. Antibiotics that kill intestinal bacteria reduce the amount of artery damage in mice on high-fat diets rich in the nutrient choline (chart, left). When mice are fed a high-fat diet, microbes in the gut convert a fat containing choline into an artery-damaging substance. This triggers more inflammation-inducing cells called macrophages (red, above) to flock into arteries (center) compared with mice fed regular chow (left). When mice on a high-choline diet are given antibiotics to kill intestinal bacteria, macrophages no longer crowd heart arteries (right). Credit: chart: Janel Kiley; images: Z. Wang et al/Nature 2011