Studies show that our gut microbes transform the food we eat into thousands of enzymes, hormones, vitamins, and other metabolites that influence everything from your mental health and immune system to your likelihood of gaining weight and developing chronic disease.
Gut bacteria can even affect your mental state by producing mood-altering neurotransmitters like dopamine, which regulates pleasure, learning, and motivation, and serotonin, which plays a role in happiness, appetite, and desire sexual. Some recent studies suggest that the composition of your gut microbiome may even play a role in how well you sleep.
But the wrong mix of microbes can produce chemicals that flood the bloodstream and form plaque in the coronary arteries. The hormones they produce can influence appetite, blood sugar levels, inflammation, and the risk of developing obesity and type 2 diabetes.
The foods you eat, along with your environment and lifestyle, seem to play a much bigger role in shaping your gut microbiome than genetics. In fact, genes have surprisingly little effect. Studies show that even identical twins share only a third of the same gut microbes.
Your ‘good’ microbes feast on fiber and variety
In general, scientists have found that the more diverse your diet, the more diverse your gut microbiome. Studies show that a high level of microbiome diversity correlates with good health and that low diversity is linked to higher rates of weight gain and obesity, diabetes, rheumatoid arthritis, and other chronic diseases.
Eating a wide variety of fiber-rich plants and nutrient-dense foods appears to be especially beneficial, said Tim Spector, a professor of genetic epidemiology at King’s College London and founder of the British Gut Project, a collaborative effort to map thousands of individual microbiomes.
Even if you already eat a lot of fruits and vegetables, Spector advises increasing the variety of plant foods you eat each week. A quick way to do this is to start using more herbs and spices. He can use a variety of green leafy vegetables instead of one type of lettuce for his salads. Adding a variety of fruits to your breakfast, adding several different vegetables to your stir fry, and eating more nuts, seeds, beans, and grains is good for your microbiome.
These plant foods contain soluble fiber that passes through much of your gastrointestinal tract largely unaffected until it reaches your large intestine. There, gut microbes feast on it, metabolizing and converting fiber into beneficial compounds like short-chain fatty acids, which can reduce inflammation and help regulate appetite and blood sugar levels.
In one study, scientists followed more than 1,600 people for about a decade. They found that the people who had the highest levels of microbial diversity also consumed the highest levels of fiber. And they even gained less weight during the 10-year study, which was published in the International Journal of Obesity.
Groups of ‘bad’ microbes thrive on junk food
Another important measure of gut health is the ratio of a person’s beneficial microbes to potentially harmful ones. In a study of 1,100 people in the United States and Britain published last year in Nature Medicine, Spector and a team of scientists from Harvard, Stanford and other universities identified groups of “good” gut microbes that protected people against disease. cardiovascular diseases, obesity and diabetes. They also identified groups of “bad” microbes that promote inflammation, heart disease and poor metabolic health.
While it’s clear that eating lots of fiber is good for your microbiome, research shows that eating the wrong foods can tip the scales in your gut in favor of disease-promoting microbes.
The Nature study found that “bad” microbes were more common in people who ate lots of highly processed, low-fiber foods high in additives like sugar, salt and artificial ingredients. This includes soft drinks, white bread and white pasta, processed meats, and packaged snacks like cookies, chocolate bars, and potato chips.
The findings were based on an ongoing project called the Zoe Predict Study, the world’s largest personalized nutrition study. It’s run by a health sciences company Spector and his colleagues created called Zoe, which allows consumers to analyze their microbiomes for a fee.
Add more spices, nuts, plants, and fermented foods to your diet
Once you start increasing the variety of plant foods you eat every day, set a goal of trying to eat about 30 different plant foods a week, says Spector. That may sound like a lot, but you’re probably already eating a lot of these foods.
The sample menu shows how in just three meals over the course of the week you can easily eat 30 different plant foods.
- One day, start your morning with a bowl of plain yogurt topped with sliced bananas and strawberries, a sprinkle of cinnamon powder, and a handful of mixed nuts (containing almonds, walnuts, cashews, hazelnuts, and peanuts). Meal count: 8 plant foods
- On another day, have a leafy salad with at least two mixed greens, tomatoes, carrots, broccoli, and bell peppers. Add herbes de Provence, a seasoning that typically contains six herbs, to grilled chicken or fish. Meal count: 12 plant foods
- Later in the week, tuck into pesto-seasoned chicken (contains basil, pine nuts, and garlic) and enjoy a bowl of brown rice with onions and beans and a side of sautéed greens with green and yellow squash, mushrooms, and shallots. Meal count: 10 plant foods
Another way to nourish your gut microbiota is to eat fermented foods like yogurt, kimchi, sauerkraut, kombucha, and kefir. Microbes in fermented foods, known as probiotics, produce vitamins, hormones and other nutrients. When you eat them, they can increase the diversity of your gut microbiome and improve your immune health, said Maria Marco, a professor of food science and technology who studies microbes and gut health at the University of California, Davis.
In a study published last year in the journal Cell, Stanford researchers found that when they assigned people to eat fermented foods every day for a period of 10 weeks, their gut microbial diversity increased and their levels of inflammation decreased.
“We are increasingly developing a very rich understanding of why microbes are so good for us,” Marco said.
Have a question for Anahad about healthy eating? Email EatingLab@washpost.com and we may answer your question in a future column.
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