A diverse diet doesn't necessarily mean a healthy diversity in intestinal bacteria. In fact, it may mean just the opposite.
It’s important for the human body to have a diverse set of bacteria in the gut; after all, low diversity is linked to many diseases. But mixing up your diet might not lead to a wider spectrum of microbes living in your midsection.
According to researchers led by Dr. Daniel Bolnick of the University of Texas at Austin, the more diverse a fish’s diet, the less diverse the microbes in its gut. “We're still scratching our heads as to why,” Bolnick says. “We also don't really know yet whether this reduced microbial diversity is good or bad, though some diseases (colitis, for instance, and obesity) are associated with low microbial diversity.”
Studies have shown that diet and environment can affect the bacteria in the gut, but most studies have only looked at a single factor at a time, for instance the amount of fat in a person’s diet. Bolnick and his team wanted to go further to test how combinations of foods could affect bacteria in the gut.
“Treating diet as a set of discrete and different options isn't realistic though,” he says. So they turned to two species of fish, the threespine stickleback and the Eurasian perch, and monitored their diets. The researchers thought the fish who ate a variety of foods would have more diverse gut bacteria than the fish who stuck to one type. It turned out the opposite was true.
Fish and humans are very different, but they do share many of the same immune cells and genes in the gut lining. At the same time, our intestines are structured differently, and our diets are different.
“It remains an open question whether the patterns identified in our study will also apply to humans,” Bolnick says. He’s game to look into it, though. Bolnick plans to conduct diet experiments in humans to see if diverse diets lead to the same effect in humans.