The 'breakthrough' study, published in Nature, investigated how short-term alterations to diet affect the composition of gut bacteria that make-up our intestinal microbiota - finding that alterations to dietary patterns can lead to rapid changes in microbial ecology.
Led by Lawrence David of Harvard University, the team noted that while long-term dietary intake is known to influence the structure and activity of the trillions of microorganisms residing in the human gut, it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient changes.
"Here we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression," explained the Harvard-led team who revealed that consumption of the animal-based diet that included meat and dairy but very few carbohydrates increased the abundance of bile-tolerant microorganisms (such as Alistipes, Bilophila andBacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii).
David and his colleagues noted that while research in mice had already suggested that the microbiome could change within a day, until now the effect hadn’t been replicated in humans.
“It’s exciting and gratifying to find out this holds up in people,” said David. “We’re getting an increasing appreciation of how flexible and responsive the microbiome is, even on a very short time scale.”
Indeed, the Harvard researcher and his team also suggested that the rapid adaptability to different foods could be used to control illnesses tied to the microbiota.
"Increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease," noted the team. "In concert, these results demonstrate that the gut microbiome can rapidly respond to altered diet, potentially facilitating the diversity of human dietary lifestyles."
The researchers recruited nine volunteers, who were each given the two extreme diets for five days with a washout period between them.
The animal-based diet, focused primarily on meat and cheese, said David: "Breakfast was eggs and bacon. Lunch was ribs and briskets, and then for dinner, it was salami and prosciutto with an assortment of cheeses," he said - noting that the volunteers had pork rinds for snacks.
After a break, the volunteers began the second, fibre-rich diet, which focused primarily on foods from plants - including granola, rice, lentils, fruit and vegetables.
While David conceded that the animal-based diet is 'a little extreme', he did suggest that the plant-based diet "is one you might find in a developing country."
The Harvard-led research team analysed the make-up of the volunteers' microbiota before, during and after each diet.
The findings were stark, said David: "The relative abundance of various bacteria species looked like it shifted within a day after the food hit the gut."
After around three days on the diets, not only had the make-up of the microbiota changed, but so had the behaviours of the gut bacteria.
"The kind of genes turned on in the microbes changed in both diets," explained David.
Published online ahead of print, doi: 10.1038/nature12820
"Diet rapidly and reproducibly alters the human gut microbiome"
Authors: Lawrence A. David, Corinne F. Maurice, Rachel N. Carmody, et al