Scientists know that the trillions of bacteria and other microbes that live in our intestines play important health roles and affect our risk of obesity, heart disease, type 2 diabetes, and a host of other conditions. Now, a major new international study has found that the makeup of these microorganisms, collectively known as our microbiomes, largely depends on what we eat.
When analyzing the diet, health, and microbiomes of more than a thousand people, researchers found that a diet high in nutritious whole foods supports the growth of beneficial microbes that promote health. However, a diet full of highly processed foods with added sugar, salt, and other additives had the opposite effect, promoting gut microbes that have been linked to poorer cardiovascular and metabolic health.
The researchers found that what people ate had a greater impact on the composition of their microbiomes than their genes. They also discovered that a variety of plant and animal foods were linked to a more favorable microbiome.
A critical factor was whether or not people ate foods that were highly processed. People who tended to eat minimally processed foods like vegetables, nuts, eggs, and seafood were more likely to harbor beneficial gut bacteria. In contrast, consuming large amounts of juices, sweetened beverages, white bread, refined grains, and processed meats has been linked to microbes that have been linked to poor metabolic health.
“It goes back to the age-old message of eating as much whole and unprocessed foods as possible,” said Dr. Sarah E. Berry, nutritionist at King’s College London and co-author of the new study. which was published in Nature Medicine on Monday. “What this research is showing for the first time is the relationship between the quality of the food we eat, the quality of our microbiomes and, ultimately, our health outcomes.”
The results could one day help doctors and nutritionists prevent, or perhaps even treat, some diet-related diseases, and enable them to prescribe personalized diets for people based on the unique makeup of their microbiomes and other factors.
Many studies suggest that there is no one size fits all diet. For example, the new study found that while some foods are generally better for health than others, different people can have wildly different metabolic responses to the same foods, partly mediated by the types of microbes living in their gut.
“What we found in our study was that the same diet in two different people does not lead to the same microbiome or metabolic response,” said Dr. Andrew T. Chan, co-author and professor of medicine at Harvard Medical School and Massachusetts General Hospital. “There are many variations.”
The new findings come from an international study on personalized nutrition called Predict the world’s largest research project designed to look at individual reactions to food. The study was started in 2018 by British epidemiologist Tim Spector and has tracked over 1,100 mostly healthy adults in the US and UK, including hundreds of identical and non-identical twins.
The researchers collected data on a variety of factors that affect metabolism and disease risk. They analyzed the diet, microbiomes and body fat of the participants. They took blood samples before and after meals to check their blood sugar, hormone, cholesterol, and inflammation levels. They monitored their sleep and physical activity. And for two weeks they had continuous glucose monitors worn that tracked their blood sugar responses to different meals.
Researchers were surprised to discover that genetics played a minor role in shaping a person’s microbiome. Identical twins have been found to share only 34 percent of the same gut microbes, while people who are unrelated share about 30 percent of the same microbes. The makeup of each person’s microbiome seemed more dependent on what they ate, and the types of microbes in their guts played a large role in their metabolic health.
The researchers identified clusters of so-called good intestinal bugs that were more common in people who ate varied and high-fiber crops like spinach, broccoli, tomatoes, nuts, and seeds, as well as minimally processed animal foods like fish and high-fat yogurt. They also found clusters of “bad” intestinal bugs that were common in people who regularly consumed highly processed foods. A common denominator among highly processed foods is that they tend to be very low in fiber, a macronutrient that helps feed good microbes in the gut, the researchers said.
The “good” strains of gut microbes included Prevotella copri and Blastocystis, both of which were associated with lower levels of visceral fat that accumulates around internal organs and increases the risk of heart disease. These microbes also appeared to improve blood sugar control, an indicator of diabetes risk. Other beneficial microbes have been linked to decreased inflammation and lower post-meal increases in blood lipid and cholesterol levels, all of which play roles in cardiovascular health.
The new study was funded and supported by Zoe Global, a health science company, and the Wellcome Trust, a UK non-profit organization, and several public health groups.
Dr. Berry said the results suggest that by looking at microbiome profiles, they can identify people at high risk of developing metabolic diseases and intervene early. She and her colleagues are now planning a clinical study to test whether asking certain people to change certain foods in their diet can alter the levels of good and bad microbes in their gut and then improve their health.
“We believe there are many small changes that people can make that can have a huge impact on their health that may be mediated by the microbiome,” she said.