Risk factors for cardiovascular disease, such as obesity, hypertension, hyperlipidemia, diabetes and overt cardiometabolic dysfunction, are related to poor nutritional content and dietary patterns reflecting the standard American diet. Interestingly, an emerging player in cardiovascular health is the relationship between dietary patterns and their impact on gut microbiome diversity.^1,2 The "gut-heart axis" appreciates the intricacies of gut biodiversity and how their metabolites are related to cardiovascular health and outcomes.³

The gut microbiome is a powerful endocrine and immunological organ composed of trillions of microorganisms.^3,4 Analyses of atherosclerotic plaque have shown fatty deposits, containing bacterial DNA, some originating from the gut microbiome. This raises the concern that the gut microbiome, and its metabolites, plays a role in cardiovascular function.⁵ It metabolizes dietary components into bioactive molecules that circulate systemically. Short-chain fatty acids (SCFAs), such as butyrate and acetate, are key bioactive molecules, shown to exhibit anti-inflammatory and vasoprotective effects.^3,6-10

Dysbiosis, or poor gut biodiversity, is associated with systemic inflammation, impaired endothelial function and insulin resistance, all contributing to increased cardiovascular risk.¹¹ Metabolites from poor gut health contribute to the development of atherosclerosis. Trimethylamine-N-oxide, derived from red meat, is implicated in promoting atherosclerosis, vascular calcification, endothelial dysfunction and platelet hyperreactivity, likely through pathways involving inflammation, oxidative stress and altered cholesterol metabolism.^3,12-14

Phenylacetalglutamine (PAG), another metabolite, enhances platelet activation and thrombosis potential via adrenergic receptor signaling. Experimental models demonstrate that elevated PAG directly induces vascular and cardiac dysfunction.^3,15,16 Microbiome studies confirm that the abundance of PAG-producing pathways is higher in individuals with atherosclerotic cardiovascular disease.¹⁷

The Power of Fiber

Dietary patterns and nutritional diversity play a fundamental role in gut health. Diets rich in fiber are shown to positively impact microbiome diversity.³ The Mediterranean and plant-based diets increase fiber intake, ultimately helping diversify the microbiome.¹⁸ Fiber has long been associated with gastrointestinal benefits, as well as impacting cardiometabolic health. For example, increased fiber leads to increased satiety, which can lead to weight loss and ultimately improve lipid profiles, decrease insulin resistance and decrease waist circumference.¹⁹ Also, dietary patterns naturally rich in fiber reduce hypertension.¹⁹

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Soluble fibers, found in oats, peas, beans, apples, bananas, avocados, citrus fruits, carrots, barley and psyllium, are effective at lowering serum cholesterol and improving glycemic control through their viscous properties and fermentability.^20-23 Insoluble fibers, found in whole-wheat flour, wheat bran, nuts, beans, cauliflower, green beans and potatoes, support gastrointestinal health, microbiota diversity and increased satiety.^21-23

Dietary fiber serves as a prebiotic substrate for beneficial gut bacteria, such as Lactobacillus and Bifidobacterium, leading to production of SCFAs that in turn enhance endothelial function, reduce oxidative stress and promote regulatory T cell development, overall decreasing inflammation.^3,6-10,24

Robust epidemiological evidence comes from the National Health and Nutrition Examination Survey (NHANES) and European Prospective Investigation into Cancer and Nutrition (EPIC) cohorts.^25,26 NHANES data demonstrated that increased dietary fiber intake and density are independently associated with reduced long-term predicted cardiovascular disease risk (especially in young to middle-aged adults), lower levels of C-reactive protein, and decreased prevalence of metabolic syndrome and obesity.^25-28 EPIC similarly demonstrated that higher total daily fiber intake was associated with reduced risk of ischemic heart disease (IHD) and cardiovascular disease mortality, with a 10 g/day increase in fiber intake associated with a 10-15% decrease in risk of fatal IHD.^26,29,30

Despite the evidence, <10% of Americans meet the recommended daily intake of 25-38 grams of fiber per day.²⁵ Contributors to low fiber intake are adherence to the standard American diet, rich in ultra-processed foods, reduced advocacy and socioeconomic drivers of health, such as food insecurity.25,31

Incorporating dietary assessments into primary care and specialized cardiovascular patient visits can help uncover barriers to access. Cardiologists should advocate for fiber-rich diets, such as plant-based or Mediterranean, that emphasize fruits, vegetables, whole grains and legumes.¹⁸ Multidisciplinary practice involving registered dietitians, weight management and behavioral health can help guide patients to make sustainable dietary changes.

Research continues to explore ways to optimize the gut microbiome to improve cardiometabolic outcomes beyond fiber, investigating dietary polyphenols, resistant starches and fermented foods. Interventions such as postbiotics, targeted probiotics and even fecal microbiota transplantation are being studied too.³²

Key areas for future research include elucidating types of fiber that most effectively reduce cardiovascular risk and identifying gut microbiota phenotypes and their metabolic pathways that provide cardioprotective benefits. Long-term, large-scale randomized, controlled trials will be needed to solidify the causal relationship between gut health and cardiometabolic outcomes.

The relationship between the gut microbiome, dietary fiber and cardiometabolic health represents a promising frontier in preventive cardiology. By promoting a diverse and metabolically active microbiome, through a high-fiber diet, we can improve lipid metabolism, glycemic control and inflammation, contributing to improved cardiometabolic health and reduced cardiovascular outcomes. The 2019 ACC/AHA Primary Prevention Guideline gave a class 1 recommendation for promoting a plant-forward diet, making this part of guideline-directed therapy.

References

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Keywords: Cardiology Magazine, ACC Publications, Gastrointestinal Microbiome, Dietary Fiber, Anti-Inflammatory Agents, Heart Disease Risk Factors