Heart health is shaped by more than one part of the body. What we eat, how active we are, and whether we smoke all matter, but researchers are also examining the relationship between the gut microbiome and heart health more closely. The microorganisms living in our digestive tract help break down components of our food and produce molecules that may influence processes related to cardiovascular health.
This connection is known as the gut-heart axis. In this article, we explore how the gut microbiome may influence the heart, what human studies tell us about diet and probiotics, and the everyday habits that support both gut and cardiovascular health.
The gut-heart axis is the relationship between the gut and the cardiovascular system. This relationship is two-way, meaning that changes in the gut may affect the cardiovascular system, and cardiovascular health may also influence the gut 1. Much of the research focuses on the gut microbiome, the community of microorganisms that live in your digestive tract. When they break down food, they produce compounds that can enter the bloodstream 2. Some may influence inflammation or the way the body processes sugars and fats, both of which matter for cardiovascular health 3.
That does not necessarily mean that a particular change in gut bacteria will lead to a measurable change in heart health. Researchers are still working out what the links between gut health and heart disease mean in practice.
The gut-heart connection involves more than the substances gut microbes produce. The mix and diversity of microbes may matter, as may the gut barrier, which helps control what passes from the intestine into the bloodstream. In one trial involving older adults, a polyphenol-rich diet changed gut microbes and reduced a measure of intestinal permeability 4. Another trial found that a fermented-food diet increased microbial diversity and reduced inflammatory markers in healthy adults 5. An observational study found that lower microbial diversity was associated with higher estimated cardiovascular risk, suggesting a link between gut microbes and cardiovascular health 6.
One way gut bacteria may influence cardiovascular health is through the compounds they produce when they break down food. Microbial metabolites are small compounds produced when the microbiome in your intestines breaks down food. These metabolites act as messengers that travel through the bloodstream and interact with organs in the body, including the heart 7.
One example is short-chain fatty acids (SCFAs), which gut bacteria produce when they ferment dietary fibre. Researchers are studying how these compounds affect inflammation, metabolism, and blood pressure. Much of what we know about how SCFAs might affect blood pressure comes from laboratory and animal studies. These suggest that SCFAs can interact with receptors in blood vessels and the kidneys, potentially impacting vascular relaxation and blood pressure regulation 8,9. Research is still ongoing to evaluate how important these mechanisms are in people and whether increasing SCFA production leads to meaningful cardiovascular benefits.
Another important metabolite is trimethylamine N-oxide (TMAO). Its production begins when gut microbes convert certain dietary compounds into trimethylamine; the liver then turns this into TMAO. Diet can affect TMAO levels. In a controlled feeding study, blood TMAO levels were higher after four weeks of a red-meat diet than after diets based on white meat or non-meat protein 10. Higher levels of TMAO in the blood have been linked to a greater risk of heart and blood vessel disease. Researchers are investigating whether TMAO affects how the body handles cholesterol, increases the likelihood of blood clots, and contributes to plaque buildup in the arteries 11.
Gut microbes also modify bile acids, which the liver makes to help digest fats. These modified bile acids can influence metabolic and inflammatory signalling 12. Taken together, these examples show why it is too simplistic to label individual metabolites “good” or “bad”. Their effects depend on diet, the wider microbiome, and an individual’s health. Much of the evidence is still being worked out, particularly regarding effects on cardiovascular outcomes in people.
What you eat affects both your cardiovascular health and the food available to your gut microbes. Fibre is one example. Found in food such as beans, oats, and wholegrains, it reaches the large intestine, where microbes ferment it to produce SCFAs 13. In a small dietary trial, increasing fibre increased the gut microbiome’s capacity to break down carbohydrates, although it did not increase overall microbial diversity during the study 14.
Variety matters too. Eating a wider range of plant foods, including vegetables, fruit, pulses, nuts, seeds, and wholegrains, has been linked to a more diverse gut microbiome 15. A Mediterranean-style diet brings many of these foods together, alongside olive oil and fish. In a large trial involving people at high cardiovascular risk, those assigned to Mediterranean diets supplemented with olive oil or nuts had fewer major cardiovascular events than those assigned to a reduced-fat diet 16. A smaller trial also found changes in the gut microbiome and lower blood cholesterol after eight weeks on a Mediterranean diet 17.
At the other end of the spectrum, diets high in ultra-processed foods have been associated with higher cardiovascular risk 18. In an eight-week crossover trial, adults with overweight or obesity lost more weight on a minimally processed diet than on an ultra-processed diet, even though both diets followed UK healthy-eating guidance 19.
Probiotics and heart health are another area of interest in gut-heart research. Studies have explored whether certain strains can influence blood pressure and cholesterol levels, with some reporting modest improvements in these cardiovascular risk factors 20. Researchers are also investigating how probiotics might work, for example, by changing how the gut processes bile acids or influencing the compounds produced by other gut microbes 21,22.
What makes this research particularly interesting is that effects may depend on the strain used. In one trial, Lactobacillus reuteri NCIMB 30242 helped lower low-density lipoprotein (LDL), or “bad” cholesterol, in adults with high cholesterol 23. Results like this offer a promising direction for research; however, some limitations do remain. Studies have tested different strains, doses, and treatment periods, making their results difficult to compare. Most have measured risk factors, such as blood pressure or cholesterol, rather than whether probiotics reduce the risk of heart attacks or strokes. More research is needed to establish which strains, if any, offer meaningful cardiovascular benefits over time.
Probiotics are best viewed as one part of a wider approach to cardiovascular wellbeing, alongside a balanced diet and other established healthy habits.
Supporting the gut-heart connection does not require a focus on any single food or supplement. Everyday dietary habits offer a more useful starting point. A varied intake of fibre-rich plant foods, including beans, lentils, vegetables, fruit, and wholegrains, can be encouraged across meals 24,25. Fibre provides a substrate for gut microbes, while an overall healthy dietary pattern is an established part of cardiovascular care.
Regular movement matters too. Physical activity supports cardiovascular health, especially for those at risk, and researchers are exploring how it may affect the gut microbiome 26–29. If you smoke, stopping is one of the most important steps you can take for your heart 30. Limiting alcohol can also help reduce cardiovascular risk 31.
It’s worth looking at the bigger picture rather than any one gut-health habit. Blood pressure, cholesterol, and blood sugar all matter for cardiometabolic health, alongside what you eat, how active you are, and whether you smoke.
The gut-heart axis offers another reason to value everyday habits that support cardiovascular health. Eating a variety of fibre-rich plant foods provides gut microbes with material to work with, while Mediterranean-style eating patterns have been shown to benefit the heart. Research into probiotics is also encouraging, with certain strains showing modest improvements in risk factors like cholesterol and blood pressure. The strongest approach is still to look at the whole picture: a varied diet, regular movement, not smoking, and limiting alcohol. Together, these habits support heart health while creating a favourable environment for the gut microbiome.
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