Adopted Foodways and health
Researchers Discuss Dietary Acculturation
Trillions of microorganisms live on our skin and inside our bodies—a community known as the microbiome. Most of these organisms (bacteria, archaea, fungi, protozoa and viruses) reside in our lower digestive tract.
Our gut microbiome (GMB) plays a large role in gut health and can also affect metabolism, the immune system, the central nervous system and beyond. Each person’s GMB is unique, determined by a mixture of genetics, environment, medication use and diet.
Dietary changes can affect the composition of our GMB. This knowledge prompted a question for several researchers in the NIH Microbiome, Diet, and Health Interrelationships and Nutrition and Health Disparities Implementation working groups. They presented a joint lecture, “The Gut Microbiome and Dietary Acculturation Among U.S. Immigrants.”
How do dietary changes from immigration affect the microbiome? Dietary acculturation is the process that occurs when members of a minority group adopt the eating patterns or food choices of their host country. For individuals who move to live in the U.S., that may involve adopting a more “Westernized” diet, i.e., consuming foods high in sugars and fats and low in fiber.
Western diets, said Dr. Justin Sonnenburg of Stanford University, have “very different metabolic outcomes than a more plant-based diet.”
One way to study how our GMBs have changed is to learn what they used to look like.
Sonnenburg accomplished this by studying samples obtained from the Hadza people, a hunter-gatherer community that is one of the last such communities in Africa. He found that the Hadza gut harbors microbial species that are both more diverse and distinct when compared to people from industrialized communities. One notable difference is that the Hadza have many Prevotella species, a group of bacteria that have been associated with high-fiber diets. Alternatively, industrialized guts are populated with more Bacteroides species. Some microbe types, including the Prevotella, also cycled seasonally in the Hadza, seeming to coincide with the seasonal availability of certain plants.
Interestingly, other researchers have found that the microbial diversity in non-industrialized peoples is very similar to that found in the feces of ancient (paleo) humans. Industrialization seems to coincide with a general decline in microbial diversity, as well as an increase in chronic inflammatory diseases.
“Our microbial identity has changed,” Sonnenburg said.
But how do peoples’ microbial identities change when they move to new places and alter their eating habits? To answer this question, researchers studied U.S. residents of Hispanic/Latino descent. People in this group make up 19% of the U.S. population and are widespread across the nation. About four in five study participants were born in Latin America. Diet varies from country to country, but in general, Hispanic/Latino individuals following the diet traditions of Latin America generally eat a more fiber-rich diet, with staples such as beans, fruits and vegetables.
Dr. Robert Kaplan, a professor at the Albert Einstein College of Medicine, found that duration of time spent in this country is a leading correlate among Latinos of gut microbiome diversity and prevalence of particular bacteria, such as fiber-utilizing Prevotella. Kaplan’s findings were informed by a cohort study of 16,000 Latin American adults across the U.S.
He categorized individuals into national background groups and evaluated their metabolic risk factors: incidence of conditions like hypertension, dyslipidemia, obesity and diabetes.
Interestingly, as English language use rose among U.S. Latinos, so did their body mass index (BMI). This trend held true even when Kaplan accounted for education level. Participants also provided details about their diets and self-assessed their dietary identity as Hispanic or American.
Results showed “a great degree of diversity” in the healthfulness of participants’ diets, Kaplan noted. He was able to identify three groups of dietary patterns: burgers-fries-soft drinks, fish-salad-whole grains and white rice-beans-red meat. The latter group is reflective of a traditionally Hispanic diet, and the first (Westernized or American-style) diet group is associated with fewer fiber-rich foods. Many individuals in the cohort study reported eating higher proportions of American foods than Hispanic foods as they spent more time in the U.S.
Kaplan and his team measured multiple variables and determined their role in GMB diversity and composition; time living in U.S. was a leading factor. Also, researchers learned that microbial species abundance varied by region of birth as well as diet.
Prevotella, for example, a genus of bacteria that is associated with high-fiber diets, was much less abundant in individuals who were born in the U.S. compared to people born in Latin America. Conversely, in folks born in the U.S. as well as people who relocated here from Latin America at a young age, the diets were higher in fat and protein and the gut was enriched with genus Bacteroides.
For individuals who were born in the U.S, national background did not seem to have an effect on microbial genus abundance. This suggests that Americans of Puerto Rican, Mexican and other Latino heritage all may be susceptible to changes in gut microbiome if they adapt a more Americanized lifestyle.
“The Prevotella to Bacteroides ratio was higher for those who ate more whole grains and vegetables, and lower for those who ate more meats and trans fats,” Kaplan summarized.
Birthplace and age of relocation also influenced this ratio: Individuals born in Latin America who relocated later in life had a much higher Prevotella to Bacteroides ratio than someone born in mainland U.S. or who relocated in childhood.
“Birthplace and migration do have demonstrable differences in the gut microbiome that go beyond dietary preferences,” Kaplan’s study found. “Birthplace and acculturation have lasting effects.”
Differences in GMB are also observable in other immigrant groups.
Dr. Brandilyn Peters-Samuelson, an assistant professor at Albert Einstein School of Medicine, worked with a different cohort study that follows participants over time and studies incidence of cancer and other conditions. This research involved Asian, Black, Hispanic and White groups.
The two largest groups in the cohort—White U.S.-born people and foreign-born Korean individuals—showed a significant separation in GMB communities. Peters-Samuelson also compared the Bacteroides to Prevotella ratio in all groups, and determined that it was highest in the White, U.S.-born group.
In addition, Peters-Samuelson developed a dietary acculturation index that she graphed against the GMB diversity of the study participants. Higher dietary acculturation index in foreign-born Korean individuals was “marginally associated with a decrease in GMB diversity,” although it was not statistically significant, she found.
Findings were similar for the foreign-born Hispanic group. One example of this diversity loss can be seen in the abundance of bacterial species Bacteroides plebius, which is prevalent in many Asian communities because the microbe is especially adept at digesting the complex carbohydrates in seaweed. The prevalence of B. plebius in foreign-born Koreans in the study decreased as dietary acculturation index increased. She observed similar patterns in several microbial species common to foreign-born Hispanics.
Researchers noted that there is much to learn still about the implications and process of dietary acculturation. Not all changes are deleterious, but those that are may contribute to conditions such as obesity, diabetes and cardiovascular disease.
Looking forward, Peters-Samuelson said, she wants to define and encourage “healthy” dietary acculturation.