Eat. This meal herbal was provided as part of a test of the effects of diet on gut microbes.
Lawrence David
With all the recent talk about how gut bacteria affect health and disease, it begins to seem like they could be in charge of our body. But we can have our say by what we eat. For the first time in humans, the researchers showed that a radical change in diet can quickly change the microbial composition in the gut and also change what these bacteria do. The study takes a first step to identify how these microbes, collectively the intestinal microbiome, can be used to keep us healthy.
"It is a landmark study," said Rob Knight, a microbial ecologist at the University of Colorado, Boulder, who was not involved in the work. "It changes our view of the speed of the microbiome may change."
Almost every month, a new study suggests a link between bacteria living in the gut and diseases ranging from obesity to autism, at least in mice. Researchers have struggled, however, immobilizing the links between health and the microbes in humans, in part because it is difficult to make people change their diet for weeks and months that researchers thought need to change the gut microbes and see a health effect.
But in 09, Peter Turnbaugh, a microbiologist at Harvard University, demonstrated in mice that the change in diet affected the microbiome in a day. So he and Laurent David, now a biologist calculation at Duke University in Durham, North Carolina, decided to see if the diet could have an immediate effect in humans too. They recruited 10 volunteers to eat only what the researchers provided for 5 days. Half ate only animal bacon and eggs for breakfast; spareribs and chest for lunch; salami and a selection of cheese for dinner with pork rinds and string cheese as snacks. The other half consumed a high-fiber, plant-only diet with grains, beans, fruits and vegetables. For the few days before and after the experiment, the volunteers recorded what they ate so that the researchers could evaluate how dietary intake differed.
The scientists isolated DNA and other molecules, as well as bacteria from stool samples from before, during and after the experiment. This way they could identify bacterial species were present in the intestines and what they produced. The researchers also examined the activity of genes in microbes.
Within each diet group, the differences between microbiomes volunteers began to disappear. The types of bacteria in the intestines do not change much, but the abundance of these different types have, especially in meat eaters, David Turnbaugh, and colleagues reported online today in Nature . In 4 days, the bacteria known to tolerate high levels of bile acids increased significantly in meat eaters. (The body secretes more bile to digest meat.) The activity of genes, which reflects how the bacteria were metabolizing food, has also changed a little. In eating meat, genes involved in protein degradation have increased their activity, while in food plants, other genes that help digest carbohydrates resurfaced. "What was really surprising is that the gene [activity] profiles conform almost exactly what [is seen] in herbivores and carnivores," David said. This same rapid change has occurred in the long-term vegetarian who switched to meat for the study, he said. "I'm really surprised how quickly it happened."
From the perspective of evolution, that intestinal bacteria can contribute to mitigating the effects of a rapid change in diet food, reviving quickly different metabolic capabilities based on meal consumed, may have been useful to early humans, said David. But this flexibility also has possible implications for health today.
"this is a very important aspect of a very hot area of science, "writes Colin Hill, a microbiologist at University college Cork in Ireland, which has not participated. "Perhaps by adjusting diet, we can shape the microbiome in ways that can promote health," added Sarkis Mazmanian, a microbiologist at the California Institute of Technology in Pasadena, also affiliated with the study.
But how it should be shaped is still in the air. "We are not yet at the point where we can make significant dietary recommendations to" improve "the microbiota (and host)" wrote Hill. He and others are cautious, for example, on the consequences of the increase in any bacterium, Bilophila wadsworthia , in meat eaters than in mice is associated with inflammatory bowel disease and diets high in fat. Knight said, "There is still a long way to go before causation is established"
So Hill best advice for today. "People should ideally consume a varied diet with nutrients and micronutrient-whether derived from appropriate animal or plant or a mixed system. "
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