In a randomized trial of 349 UK adults, a daily plant supplement increased 57 species of beneficial gut bacteria, compared with changes in 4 species for a probiotic. The supplement is sold by ZOE, which co-led the study.
Probiotic pills and drinks have become a multibillion-dollar business, promising to improve gut health by adding beneficial bacteria. A new trial suggests that feeding the microbes already living in the gut with a wide variety of plants may do more.
Researchers at King’s College London and the nutrition company ZOE report in the British Journal of Nutrition that a daily supplement containing more than 30 types of plants changed the composition of the gut microbiome far more than a probiotic capsule did over six weeks.
Readers should note an important detail: the supplement tested, called Daily30, is a ZOE product, and the study’s lead author, Sarah Berry, is both a professor in the Department of Nutritional Sciences at King’s College London and ZOE’s chief scientist.
Plants versus pills
The randomized controlled trial enrolled 349 adults in the UK. Participants were assigned to one of three groups. One took 30 grams a day of Daily30, a blend of more than 30 plant types including vegetables, fruits, nuts, seeds, herbs, spices and mushrooms. A second group ate 28 grams of bread croutons, matched for energy, as a control. A third took a single-strain probiotic capsule containing Lactobacillus rhamnosus.
After six weeks, the Daily30 group showed increases in 57 species of gut bacteria considered beneficial. By comparison, the probiotic group showed changes in 4 species and the control group in 14.
The direction of the changes also differed. In the plant group, the species that increased were on average those associated with favorable health markers, while those that decreased were associated with unfavorable ones. According to the researchers, that pattern did not appear in the other two groups.
Berry said the results point toward diversity rather than single ingredients. “This research suggests we should focus on plant diversity, and the role that varied fibres play in shaping the microbiome, rather than searching for a single silver bullet,” she said. She argued that nourishing existing microbes with a varied range of plants can have a greater effect on the microbiome than introducing isolated strains in a pill.
How participants felt
The trial also asked participants about their symptoms. Compared with the control group, the release reports that 55 percent of those taking Daily30 reported less indigestion, 35 percent reported less severe constipation, 18 percent reported less heartburn and 37 percent reported less flatulence. Participants also reported more energy and greater happiness.
In a subgroup of 34 people, adding Daily30 to a carbohydrate-rich meal increased reported energy, fullness and satisfaction with the meal, and reduced hunger and the desire to eat.
These outcomes were self-reported, and the release does not explain how the percentages were calculated relative to the control group, so they should be read with caution.
Why diversity may matter
The trillions of bacteria in the human gut feed largely on dietary fiber that the body cannot digest on its own. Different microbes specialize in breaking down different types of fiber and plant compounds, so a varied plant diet may support a wider range of species. When gut bacteria ferment fiber, they produce short-chain fatty acids, molecules that help maintain the gut lining and influence inflammation and metabolism.
The idea of eating 30 different plants a week has been popularized in part by earlier findings from the American Gut Project, a large citizen-science study that linked greater plant variety with a more diverse microbiome. ZOE has promoted the target widely.
Probiotics, by contrast, typically contain one or a few strains, and studies suggest that many do not colonize the gut for long. Their benefits appear to depend heavily on the specific strain and the condition being treated.
Lactobacillus rhamnosus, the strain used in the trial, is among the most widely studied probiotics. Some research suggests certain strains can help with particular problems, such as diarrhea associated with antibiotics, but evidence that probiotics improve overall gut health in healthy adults is much weaker, and professional bodies generally recommend them only for specific conditions.
Weighing the evidence
The trial has notable strengths, including randomization, a control group and a comparison with a probiotic. But several caveats apply. It lasted only six weeks, so it cannot show whether the changes persist or translate into lasting health benefits. Changes in bacterial species are an intermediate outcome, not a direct measure of disease risk. And the comparison involved one specific probiotic strain, so the results may not apply to all probiotics.
The commercial connection is also significant. Tim Spector, a professor of epidemiology at King’s College London and ZOE’s scientific co-founder, framed the findings in promotional terms. “The global supplement industry is worth billions, yet much of it is built on marketing hype rather than robust science,” he said. “For too long, consumers have been sold synthetic pills and ultra-processed powders as a quick fix.” Daily30 is itself sold as a supplement.
Independent replication would help confirm the findings. In the meantime, the underlying message, that eating a wide variety of whole plants is good for the gut, is consistent with long-standing nutrition advice and can be followed without buying any particular product.
There are also simpler ways to increase plant diversity. Mixing different vegetables into meals, choosing mixed nuts and seeds, cooking with a range of herbs and spices, and swapping refined grains for whole grains and legumes can all add variety. Many nutrition guidelines already recommend these habits for reasons that go beyond the microbiome, including lower risks of heart disease and type 2 diabetes.
Notes
- Berry, S., et al. Randomised controlled trial of a multi-plant supplement, a probiotic and a control on the gut microbiome. British Journal of Nutrition, 2026.
- King’s College London. “Eating a diverse range of plants everyday results in more favorable changes to microbiome than a probiotic.” EurekAlert!, 31 July 2026. https://www.eurekalert.org/news-releases/1138371.
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