We all have trillions of gut bacteria growing inside of us that flourish to protect our bodies. Sounds kind of gross, right? But, in reality, these tiny germs are actually what keep your immune system healthy and strong. The scientific community has long hypothesized that gut microbiome diversity can lead to improved health and wellness, but new research suggests that moving to the U.S. can have a significant — and less-than-desirable effect — on the gut microbiome of immigrants.
In a recent study conducted at the University of Minnesota, scientists examined stool samples from more than 500 women from two Asian ethnic groups, the Hmong and Karen from Thailand, which make up a large portion of Minnesota's immigrant community. They discovered that microbiome diversity dwindled by 15 percent shortly after the participants moved to the U.S.
"Studies have also shown that a microbiome lacking in diversity leads to inflammation, which can lead to leaky gut," celebrity chef and nutritionist Serena Poon told LIVESTRONG. "This means more bacterial cells are able to pass through the damaged lining of the gut, which causes heightened immune system reactions. This can lead to digestive disorders and diseases, susceptibility to food-borne illness, a weakened immune system and effects on our mental health and clarity."
In the University of Minnesota study, immigrants began to lose their native microbes within months of moving to the U.S. "You pick up the microbiome of the new country and possibly some of the new disease risks that are more common in that country, " lead researcher Dan Knights told The Washington Post. "It's been known from previous studies that people in developing nations tend to have more gut microbiome diversity and lower risk of metabolic diseases. It was also known that moving from a developing nation to the U.S. increases your risk of those diseases."
Researchers attributed the decrease in microbe diversity to the fact that the Hmong and Karen women had a significant change in diet, eating more sugar, fat and protein than than they typically ate at home. "In Southeast Asia, the native diet is rich with what is available to them locally: rice, vegetables and other plants they can forage in the nearby forest," said Poon. "This included fibrous foods such as tamarind, coconuts, palm and konjac. The indigestible fiber and carbohydrates we get from consuming plant-based, high fiber foods are critically important for supporting the beneficial bacteria that lives in our gut microbiota."
Fermenting food is also common in these cultures, which contributed to the immigrants' flourishing gut bacteria diversity. "The process of fermentation not only helps multiply the number of bacteria in food, it also contributes to the diversity of these microorganisms, resulting in food that is naturally high in a probiotics," said Poon. "So, before immigrating to the United States, people in the study consumed a diet primarily of whole foods from grains, vegetables and fermented foods, which resulted in native gut flora that was diverse in microbes."
On the other side of the equation are foods high in processed sugars, fat and protein, which make up a large part of the modern-day U.S. diet. Poon explains that these foods are lacking in fiber, and that this lack of fiber "directly affects the growth of healthy bacteria, reduces that production of short chain fatty acids, degrades the colonic mucus barrier and alternately supports the nutrient absorption for the bad bacteria."
So how can we achieve a healthy gut filled with diverse good bacteria? Poon recommends filling your fridge with fewer pre-packaged, processed foods and more fibrous, plant-based, whole grain foods. "By consuming a wide range of whole foods, we feed our gut a high variety of microbes and prebiotics to create a healthy microbiota," she said. "Along with these foods, fermented foods like kimchi, sauerkraut, yogurt and kombucha provide our guts with loads of probiotics that also help to maintain strong gut biodiversity. These are all great food sources for a healthy gut, but not integral in the diet of typical Americans."
In addition to diminished microbe diversity, Knights and his team also noticed a spike in weight gain among the study participants. Obesity rates increased sixfold after moving to the U.S.. As the diversity of their gut bacteria decreased, the immigrant's obesity rates increased, putting the Karen and Hmong at greater risk for heart disease, diabetes and strokes. Those who became obese lost an additional 10 percent of their microbe diversity, giving them less protection against illnesses than they had in Southeast Asia.
Scientists theorize that these changes are linked to their change in diet, as well as different water and possibly antibiotics. Studies with mice suggest the same, however, there is still no hard evidence linking obesity to immigrant women. That said, there is plenty of anecdotal evidence to back up Knight's study.
"I can attest that their research is actually reflected in the cases of many of my own clients," says Poon. "I've had a lot of clients who have immigrated here from another country, primarily Europe and Asia, who found that their digestive systems and weight changed within a few weeks of moving to the United States."
Regardless of whether or not weight gain is solely due to gut bacteria, Poon strongly advises her immigrant clients to avoid highly processed foods (which many Americans consume regularly) in favor of whole foods during their transition to the U.S.. She also suggests eating many of the same foods they ate in their native country, along with a few new ones, to help their bodies adjust to an American lifestyle.
"Moving from one house to another can be stressful, even if it's just a few blocks away," notes Poon. "Immigrating to a new country is full of a wide variety of stressors that will ultimately have a domino effect on our bodies, and in particular, the health of our gut bacteria."
Keeping your gut healthy also helps keep your entire body in balance. And immigrants aren't the only ones who can benefit from increased microbe diversity.
"Healthy gut bacteria is the foundation for many important systems in our body, from our adrenals, to our immune system, brain function and most noticeably, our weight and digestive system," says Poon. "Proper gut health helps to support a healthy gut barrier, which allows us to properly digest food, promote nutrient absorption and normalize glucose levels, all of which are necessary to help with weight loss."
Not sure where to start? Poon says it may be simpler than you think. "The best way to maintain a healthy gut flora is by eating a wide variety of fresh whole foods, primarily from plant-based sources such as vegetables, fruits, whole grains and legumes."
In particular, foods high in both soluble and insoluble fiber are ideal. Insoluble fiber cannot be digested by our body, however it can be digested by some of the bacteria in the gut, which promotes the growth of beneficial bacteria. So consuming fruits, vegetables, bean, grains and legumes is great for the gut," she says.