Western Diet Tied to Intestinal Disease and Allergies

All those Lucky Charms and Big Macs that people in the developed world scarf down could explain why they are more susceptible to allergies, autoimmune disorders, and inflammatory bowel disease than are residents of agrarian societies. New research suggests that people living in rural Africa have a healthier mix of microbes in their guts than do their Western counterparts, which may protect them from the intestinal diseases that are common in modern developed countries.

The human gut houses trillions of microbes, our microbiota, that help us digest and metabolize what we eat, protect us against diseases, and train our immune system to recognize and reject pathogens. As our ancestors' diets changed over time, their gut inhabitants did, too, from microbes that could easily break down the fibrous foods plentiful in early human diets to other bugs suited to the animal proteins, sugars, and starches prevalent after the advent of agriculture and animal husbandry about 10,000 years ago.

Modern sanitation and medicines have further changed the types of bacteria people encounter. Scientists have hypothesized that these dietary and sanitary changes have made people in developed countries more susceptible to gastrointestinal diseases and obesity, but so far they have been unable to establish why.

A team of researchers led by Paolo Lionetti, a pediatric gastroenterologist at Meyer Children Hospital in Florence, Italy, decided to compare the fecal microbes of healthy children from a village in Burkina Faso, in western Africa, with those from healthy Italian children. The African children ate a high-fiber, low-fat, vegetable-heavy diet that reflects what people ate at the dawn of agriculture, whereas the Italian kids had a typical Western diet, low in fiber but high in animal protein, sugar, starch, and fat.

The researchers found that the children from Burkina Faso had significantly more bacteria from the Bacteroidetes class than did the Italian children and significantly fewer Firmicute bacteria. Previous research has shown that people with more Bacteroidetes and fewer Firmicutes tend to be lean, whereas people with the opposite ratio are more likely to be obese.

Additionally, the researchers detected bacterial strains of Prevotella, Xylanibacter, and Treponema only in the children from Burkina Faso. These bacteria are excellent at breaking down fibrous foods and producing short-chain fatty acids that provide added energy. Studies have also shown that those same fatty acids help protect the intestines from inflammation, which could explain why inflammatory bowel disease is almost unheard of in African communities that eat high-fiber diets, Lionetti says.

The increased diversity of microbes in the gut also makes the body more resistant to intestinal pathogens while tempering the immune system's response to harmless molecules, leading to fewer allergies, Lionetti says. The group reports its findings online today in the Proceedings of the National Academy of Sciences.

"The intestine is the site where the immune system meets the microbiota," Lionetti says, "and we have demonstrated that diet is the most important thing for having a diverse, healthy gut." He adds that people living in Western countries could benefit from changing their diets to better reflect those of people living in Burkina Faso. "If we change our diets, then we change our microbiota," he says. "Then we can improve our health."

Justin Sonnenburg, an immunologist at Stanford University in California, says the researchers did a good job designing their study and that the results are tantalizing. "It would be fascinating to do a crossover study where people from each community swap diets to see how much variance is based on inheritance," he says. "The article really lays the groundwork for some very interesting studies in the future."