(NaturalNews) A shift in diet can dramatically change the composition of your gut bacteria in just a single day, according to a study published in the journal Nature. This may explain the strong connection between diet and certain diseases.
More than 10,000 separate species dwell naturally in the human gut, playing important roles in maintaining the health of the human digestive and immune systems. These organisms are so numerous that they outnumber our body's own cells by 10 to 1.
Scientists still know very little about the composition of human gut flora, or about how changes in this internal ecosystem can affect our health. But the research conducted thus far suggests that gut flora may play a role in obesity and certain diseases such as inflammatory bowel disease. Studies have also shown that diets high in fat and sugar may change the makeup of our internal ecosystems.
To further examine the connection between diet and gut flora, the researchers in the new study had 10 people (six men and four women) submit diet journals and fecal samples for four days as they ate their normal diets. For the next four days, all participants ate the food that was provided to them by the researchers, either a diet composed almost entirely of fruits and vegetables or one composed almost entirely of animal products. One of the participants, a lifelong vegetarian, was switched to a diet composed entirely of eggs and cheese. The participants were then returned to their normal diets and observed for another six days.
The researchers found that, within a single day of switching diets, the bacterial content of participants' fecal samples dramatically changed. Participants who were shifted over to a diet high in animal products experienced increases in bacteria with a high tolerance for bile, a fluid produced by the liver to help break down fat. The prevalence of bacteria known as Firmicutes, which break down carbohydrates, significantly decreased. Furthermore, bacterial species already common in the gut actually changed the expression of their genes to help them better digest protein.
Fewer changes were observed when participants were switched to plant-based diets significantly higher in fiber and significantly lower in fat and protein. However, the researchers did observe an increase in the expression of genes that allow bacteria to ferment carbohydrates in order to digest starch and cellulose.
The changes seen in the various diets "mirrored the differences between herbivorous and carnivorous mammals," the researchers wrote.
Although prior studies had shown that the makeup of gut flora in mice could change within a single day of a dietary shift, this effect had not previously been seen in humans.
"It's exciting and gratifying to find out this holds up in people," researcher Lawrence David said. "We're getting an increasing appreciation of how flexible and responsive the microbiome is, even on a very short time scale."
Implications for health
The flexibility of the internal ecosystem might have provided a major advantage to our foraging ancestors, David suggested.
"It creates a way of buffering nutritional changes and may have enabled ancient humans to be a little more flexible with their diet," he said.
Unfortunately, humans' symbiotic relationship with their gut flora did not evolve in an environment of abundant processed, fatty foods.
For example, another important change seen in the animal-based diet was an increase in a species of anaerobic bacteria known as Bilophila wadsworthia, which thrives in the presence of fat and has been linked to the development of colitis in mice. This may explain, in part, why high-fat diets are linked with inflammatory bowel disease.