At the same time, there was little or no increase in Americans’ consumption of fermented foods and fibre-rich plants.
That contrast is striking. Experts have found that one of the simplest and most important ways to improve your gut health is by feeding your gut microbes the foods that they thrive on. These include fruits, vegetables, beans, nuts and other foods that are high in fibre. Fermented foods like yoghurt, kimchi, sauerkraut and kefir are also good for your gut, as they contain a variety of live microbes that can influence the composition of your gut microbiome and boost your overall health.
Probiotic supplements, on the other hand, are often marketed for gut health. But there’s little evidence that they can improve or benefit gut health in healthy people, and studies suggest that, in some cases, they can actually disrupt the composition of your gut microbiome.
“For most people, probiotics can give you a sense of agency, but they may not necessarily deliver the benefit that you want,” said the lead author of the new study, Kira L. Newman, a clinical assistant professor at the University of Michigan Medical School and a microbiome researcher. “But we know that foods like fruits, vegetables and whole grains all support a healthy microbiome.”
The science on probiotic supplements
Some studies have found that taking probiotic supplements can reduce microbiome diversity and cause other unintended effects.
It’s well known from studies that fibre is fuel for your gut microbiome.
Our bodies don’t have the enzymes necessary to metabolise most of the fibre that we eat. But our gut microbes do. When we eat fruits and vegetables, fibre travels through our gastrointestinal tracts largely intact until it reaches the colon, where microbes feast on it. Our gut microbes convert fibre into short-chain fatty acids and other compounds that are good for us. These compounds help lower inflammation, improve blood sugar levels and stimulate the production of appetite-suppressing hormones.
Fermented foods are similarly good for your gut because they contain beneficial microbes. Studies have found that eating fibre-rich plants and fermented foods can increase the diversity of your gut microbiome, which is a good thing. Having a wide variety of microbial species in your gut helps to crowd out harmful pathogens and is associated with a lower likelihood of developing chronic diseases like Type 2 diabetes and high blood pressure.
Probiotic supplements, which come in the form of capsules, gummies, powders and pills, contain microbes as well. But they typically have concentrated doses of a limited number of bacterial strains. Studies have found that certain strains may be beneficial in a few limited cases, such as reducing the risk of C. difficile infections while taking antibiotics.
But some studies have found that taking probiotic supplements can reduce microbiome diversity and cause other unintended effects. In one clinical trial, scientists at Stanford assigned adults with metabolic syndrome – a group of conditions that raise the risk of heart disease, stroke and Type 2 diabetes – to take a probiotic supplement for 18 weeks. The supplement contained several strains of bacteria thought to be good for metabolic and digestive health. The researchers found that some people showed improvements in their blood pressure and triglyceride levels. But others experienced a worsening of their blood sugar and insulin levels.
The benefits of food v supplements
In general, studies have found that the more diverse your diet, the more diverse your gut microbiome.
Newman at the University of Michigan specialises in treating patients with inflammatory bowel disease. She said she was inspired to carry out her study because people frequently ask her about taking probiotic supplements to improve their gut health, but in many cases are less interested in making dietary changes – even though food plays an enormous role in gut health.
“Most of our guidelines around gastrointestinal health and gut microbiome-associated conditions don’t routinely recommend probiotics,” she added. “What we do recommend consistently for many conditions is a diet that’s rich in fruits, vegetables and whole grains.”
During the study period, average daily fibre intake did not meaningfully change among adults over age 20, hovering around 8.5 grams for every 1000 calories of food intake. That amount is far below what health authorities recommend adults eat on a daily basis – 14g of fibre for every 1000 calories. The researchers also looked at the consumption of “high microbial foods” like yoghurt, kimchi, sauerkraut, kefir, kombucha and fresh cheeses. They found that the average consumption of these foods rose only slightly.
Like Newman, Damman said that people ask him all the time if they should take a probiotic supplement. He acknowledged that for many people, making dietary changes can be very difficult. “It’s easier to just pop a pill,” he said. “And probiotics are just that – a pill or capsule that’s easy to take.”
But the reality is that, in most cases, improving your diet will give you the greatest return, he said. That means eating plenty of plants and fermented foods. “Feed the good microbes that are already in your gut,” he added.
The best ways to nourish your gut microbiome
Eat a wide variety of plants: In general, studies have found that the more diverse your diet, the more diverse your gut microbiome. One way to diversify your diet is by eating many different types of plants. You can do that by eating different leafy greens, snacking on different fruits, adding more herbs and spices to your meals, and seeking out a variety of nuts, beans, seeds and grains. For more on this strategy, read this article on the best foods to feed your gut microbiome.
Eat fermented foods. Studies have found that eating fermented foods promotes gut health and increases your gut microbiome diversity. That’s because fermented foods are loaded with friendly microbes that produce essential vitamins, nutrients, and short – chain fatty acids. They also increase the bioavailability of iron, zinc and other minerals. For more on fermented foods, read this article on why fermented foods are so good for your gut, and ways to eat more of them.
Focus on fibre-rich, budget-friendly foods. Eating a gut-healthy diet doesn’t have to be expensive. You can save money by purchasing fibre-rich but budget-friendly foods like dried lentils, apples, sweet potatoes and oat bran.
Anahad O’Connor is a columnist on The Washington Post’s Well+Being desk, where he writes about food and nutrition.