A randomized trial involving 399 adults found that adding a diverse blend of 30 whole plant foods to an otherwise unchanged diet altered substantially more types of gut bacteria than either a probiotic capsule or control food over six weeks.
By yourNEWS Media Newsroom
Increasing the variety of plant foods in the diet may reshape the gut microbiome even without a complete dietary overhaul, according to a randomized controlled trial that tracked hundreds of healthy adults for six weeks.
The ZOE BIOME study, published in the British Journal of Nutrition, examined whether diversity among plant foods could influence intestinal bacteria independently of simply eating a greater quantity of plants. Researchers enrolled 399 adults between ages 35 and 65 whose diets provided less than 20 grams of fiber per day when the study began.
Rather than asking participants to replace their usual meals, investigators assigned them to add one of three interventions to what they were already eating. One group consumed a whole-food blend containing 30 different plant ingredients. Another received a daily probiotic, while the control group consumed bread croutons.
The most extensive microbiome changes occurred among those receiving the multi-plant blend.
After six weeks, researchers detected changes in the relative abundance of 57 types of gut bacteria among participants consuming the diverse plant mixture. By comparison, 14 bacterial types shifted in the control group and only four changed in the probiotic group.
The findings suggest that exposing intestinal microbes to a broad range of plant-derived fibers and compounds may have a different effect than supplying a single probiotic strain.
The whole-food intervention provided 30 grams of fiber per day from a combination of fruits, vegetables, mushrooms, herbs, nuts, seeds, spices and whole grains. The probiotic group received 15 billion colony-forming units per day of Lactobacillus rhamnosus.
Adherence exceeded 98% in all three groups, according to the report, providing researchers with a relatively consistent comparison across the six-week period.
The participants’ low-fiber diets at the outset also reflected a much broader nutritional pattern. Public health data cited by gastroenterologist Lisa Ganjhu, D.O., indicate that approximately 95% of Americans do not consume adequate fiber.
That shortfall has attracted growing attention because plant foods provide more than fiber alone. They also introduce microorganisms and a wide variety of compounds capable of interacting with the existing gut ecosystem.
Will Bulsiewicz, author of “Fiber Fueled,” has noted that a single apple may contain as many as 100 million bacteria, arguing that people should “put down the capsule and pick up an apple.”
Researchers in the ZOE BIOME trial measured participants’ microbiome composition before and after the intervention while also collecting self-reported information about digestive symptoms, energy and happiness.
Within the plant-blend group, bacterial populations that increased were generally those associated with more favorable health characteristics, while organisms that declined tended to have less favorable associations, according to the report.
Participants consuming the plant blend also reported improvements in several everyday symptoms. They described less constipation, indigestion, heartburn and flatulence than people in the control group, along with higher reported energy and happiness.
Those symptom differences, however, did not technically reach statistical significance, an important limitation when interpreting the findings.
The digestive outcomes nevertheless address common problems. Clinical reports estimate that chronic constipation affects about 20% of the U.S. adult population.
Scientists have also increasingly studied connections between intestinal microbes and systems well beyond the digestive tract. The gut-brain axis, for example, describes communication pathways linking the intestinal environment with the nervous system.
Research has shown that microbial diversity does not necessarily produce identical effects under every circumstance. A University of Vienna study involving 74 healthy adults found that greater gut microbial diversity was associated with stronger cortisol and stress responses during acute stress testing.
Earlier research has also characterized the gut microbiota as a comparatively stable ecosystem with homeostatic processes that can push its composition back toward an established state following disruption. The magnitude of the changes seen with the 30-plant intervention therefore provides researchers with additional information about how dietary variety may influence that otherwise resilient microbial community.
The types of plants included in the blend may also be important. Research published in Nutrients has reported that commonly used herbs and spices such as garlic, ginger, turmeric, cinnamon and black pepper can promote beneficial intestinal bacteria.
Whole grains, legumes and fermented foods have likewise been identified as particularly useful dietary categories for supporting microbial diversity.
Despite the extensive microbiome changes, researchers did not find meaningful changes in blood sugar control, cholesterol or inflammatory blood markers during the six-week trial.
Investigators said that result was not unexpected because the study participants were metabolically healthy and did not begin the trial with existing cardiometabolic risk factors that might have allowed larger measurable improvements.
The relatively short duration was another limitation. Six weeks may be sufficient to identify changes in bacterial populations but not necessarily enough time for downstream metabolic effects to become measurable.
The intervention itself also differed from simply assembling 30 separate plant foods in the kitchen. Participants received the diverse ingredients in a powdered whole-food blend, and the study population consisted of healthy adults rather than people with metabolic or gastrointestinal diseases.
The microbiome findings themselves also did not technically reach statistical significance, according to the report.
Researchers and nutrition writers have proposed several reasons dietary fiber may exert effects beyond bowel function. Certain gut bacteria ferment plant fibers and produce short-chain fatty acids, compounds involved in communication throughout the body.
Joseph Mercola has described short-chain fatty acids generated by fiber-consuming bacteria as “major epigenetic communicators” capable of communicating with DNA.
Diet composition can simultaneously influence which microbes receive the substrates they need to thrive. Alan Logan and Susan Prescott wrote in “The Secret Life of Your Microbiome” that highly processed foods are “tinkered with to maximize the odds that all of us will return to them.”
The ZOE BIOME trial took a different approach by emphasizing variety rather than requiring participants to abandon their existing eating patterns. That design allowed investigators to test whether simply adding diverse plant foods could produce measurable microbial changes.
The strategy can also be adapted to ordinary meals without necessarily counting large servings of every ingredient.
The report suggested thinking in terms of individual “plant points,” with each different plant contributing to overall dietary diversity. A handful of walnuts, a spoonful of flaxseed and a small amount of turmeric, for example, would each represent a separate plant food.
Seeds, herbs, spices and nuts can be added as toppings or incorporated into foods already being eaten, while whole grains, legumes and fermented foods offer additional ways to expand dietary variety.
That emphasis reflects advice from Mithu Storoni in “Stress-Proof,” who wrote that people “should be aiming toward diversity” because “a diverse microbiota is resilient and can adapt to change.”
Rather than demonstrating that one specific fruit, vegetable or supplement is responsible for a healthier microbiome, the six-week experiment points toward the cumulative effect of exposing gut bacteria to many different plant foods.
As a review of the ZOE BIOME findings put it: “Plant diversity matters just as much as plant quantity when it comes to gut health.”
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