Understanding the gut-heart connection (SQ-148)
The risk of heart disease depends on a number of factors such as age, obesity, high blood pressure, smoking, sedentary lifestyle and an unhealthy diet. Can your gut affect your heart too? Is there a connection between gut health and heart disease?
Research suggests that unhealthy gut microbiome can increase your risk of heart disease. Let’s explore the gut-heart connection in this blog and find out how your diet may play an important role in shaping the health and diversity of your gut flora.
Gut microbiome and your health
Gut microbiome refers to the trillions of microorganisms that reside inside our body, especially in the large intestine. This complex ecosystem of microorganisms includes viruses, fungi and different species of bacteria. These microbes play a big role in your health and produce substances or metabolites that can have both good and bad effects on our health.
A healthy gut microbiome is important for healthy digestion and is involved in the synthesis of various nutrients such vitamin B12, vitamin K, folic acid, biotin and thiamine. It also helps in proper absorption of nutrients. If you are suffering from poor gut health, you may be at risk of developing nutritional deficiencies.
This massive colony of microorganisms not only determines your gut health but also affects your immunity, heart health and nervous system health. Your gut microbiome talks to your brain and central nervous system to regulate functions like digestion, metabolism and hormone production. Research suggests that the bacterial composition in your gut also controls your immunity and affects your mood and brain health. So, it is extremely important to maintain a balance of good and bad bacteria. Any imbalance can lead to poor immune function, obesity, poor mood, autoimmune disorders and even heart disease.
Unhealthy gut and heart disease: Is there a link?
Researchers have highlighted a number of mechanisms that explore how the status of your gut health may affect your heart disease risk. The microbes dwelling within our intestine digest the food and produce compounds known as metabolites. These by-products or metabolites have a wide-ranging effect on our health. For example, certain bacteria help in the fermentation of non-digestible fibres, a process that leads to the production of short chain fatty acids (SCFAs) such as butyrate. SCFAs are known to benefit your health, including your gut and heart health. Similarly, some bacteria in your gut release harmful compounds that can damage your health. Let’s discuss this in detail.
In the past few years, scientists have been exploring how any shift in the gut microbiome can influence your overall health and increase your risk of chronic disease and how your diet and food choices play a very big role in maintaining the balance and diversity of the gut microbiome. Besides your diet, age, metabolic disorders, gastrointestinal disorders, use of antibiotics, consumption of alcohol and smoking also play a huge role in altering the diversity and function of your gut microbiome.
When you eat animal-based foods that contain carnitine and choline, certain bacteria in your gut break down these nutrients into a compound called trimethylamine (TMA). Your liver then metabolizes TMA into Trimethylamine-N-oxide, or TMAO, high amounts of which can lead to an increased risk of atherosclerosis, which is considered a major cause of heart disease and stroke.
Studies show that high levels of TMAO are linked with heart disease risk and that the levels of TMAO can be used to predict major cardiovascular events, independently of typical risk factors linked with cardiovascular disease.  
This study explored how plant-based diet can reduce the risk of heart disease by reducing the levels of trimethylamine N-oxide (TMAO). However, according to some ongoing studies, TMAO will be produced in large quantities only when the specific bacteria (with the ability to convert choline into TMA) is present in the gut. For example, vegetarians don't have the bacteria that is responsible for metabolizing carnitine into plaque promoting TMAO. This means the production of TMAO from carnitine depends on your gut microbiota, which appears to be different in vegetarians and non-vegetarians.
Overall, it appears that plant-based diet may help to contribute to a healthy gut microbiome. Studies show that the gut composition in vegans have unique characteristics, such as reduced number of harmful, disease-causing bacteria and increased number of friendly and protective bacteria. [3-5]
Leaky gut and heart disease
The lining of your intestine is very selective with the substances that can get into your blood vessels. In a healthy gut, this lining has tight junctions that prevent toxins, waste material, harmful bacteria and large undigested food particles from entering into circulation in the blood.
Some factors can compromise the health and integrity of the intestinal barrier, thus exposing the bloodstream and consequently the immune system to a number of unwanted particles. These factors include poor lifestyle choices (excessive drinking and smoking) and unhealthy diet (consisting of processed foods that contain excessive sugar, trans fat, food additives and artificial colouring).
Certain health conditions, intestinal infections, chronic stress and nutritional deficiencies can also damage and weaken this protective intestinal barrier. Any imbalances in the number and diversity of the gut microbiome can lead to gut dysbiosis, another major risk factor for leaky gut. The damaged intestinal lining then develops large holes or spaces that allow unwanted content from your gut to leak into the bloodstream. This condition is known as leaky gut, where the lining of the small intestine loses its barrier function and becomes too porous.
What happens when harmful, disease-causing bacteria and their metabolites reach the blood system? Your immune system views these substances as foreign (as they don’t belong there). It goes into a fighting mode and produces inflammatory substances to attack these foreign particles, causing pain and inflammation. Inflammation arising from leaky gut is known to cause plaque and blockages in the arteries. In fact, inflammation also destabilizes plaque in the arteries. Unstable plaque deposits can rupture and block the arteries, increasing the risk of heart attack and stroke. Studies show that people with heart disease are more likely to have leaky gut in comparison to healthy people. Another theory suggests that a leaky gut allows pathogens to enter the vascular system causing inflammation and damage to the artery walls.
When this inflammatory response goes on for a long time, your immune system may even start to attack its own healthy tissues, leading to autoimmune conditions such as Hashimoto’s disease. Leaky gut can also cause allergies, food sensitivities, irritable bowel syndrome (IBS), Crohn’s disease, celiac disease and more.
Lipopolysaccharides (LPS) are another cause of concern when it comes to your heart health. LPS is a toxin found in the outer membrane of Gram-negative bacteria and is known to trigger unwanted inflammatory responses if they reach the bloodstream. A leaky gut with increased permeability increases the risk of LPS (and other unwanted toxins) spilling into the bloodstream. In people with healthy intestinal lining, LPS is contained within the intestines and causes no harm.
Studies have found out that people with inflammatory bowel disease, obesity, celiac disease and rheumatoid arthritis have a lesser diverse gut microbiome than those present in otherwise healthy people.
SIBO and Heart Disease
Small intestine bacterial overgrowth (SIBO) is a condition where there is an excessive growth of the wrong kind of bacteria in the small intestine. This imbalance of the micro-organisms can cause painful and uncomfortable symptoms such as gas and diarrhoea. SIBO can lead to poor digestion and absorption of nutrients. Your body maintains a healthy balance of gut flora with the help of enzymes, bile acids, gastric acids, and proteins of the immune system. If you have an immune system that is not working efficiently or you have reduced production of gastric acid (possibly due to H. Pylori infection or from long term use of antacids and proton pump inhibitors), all of this can lead to the destruction in the fine balance of the gut flora. Overuse of antibiotics can also disrupt this balance.
In addition, small intestine dysmotility can also contribute to SIBO, where the muscles of the small intestine don't contract and relax the way they should. This kind of movement is important for pushing the digested food and waste into the large intestine. When this movement is slow, the waste in the small intestine remains there for a long time, enabling bacteria there to breed and multiply. Small intestine dysmotility can be caused by conditions like hypothyroidism.
Excessive growth of bacteria in the small intestine produce gas and metabolites that trigger pain and diarrhoea. These bacteria quickly overpower the population of good bacteria and feed on nutrition that is meant for our body. Abdominal pain, distension, bloating, too much gas, diarrhoea, constipation and indigestion are some symptoms of SIBO.
There is a body of research that shows that small intestine bacterial overgrowth (SIBO) might be considered as a risk factor for coronary artery disease. In patients with SIBO, there is an increased production of bacterial by-products that may increase the risk of coronary artery disease.  A 2018 study showed the patients with SIBO had a higher frequency of coronary artery disease, type 2 diabetes and kidney disease.  Other studies also show the connection between SIBO and poor outcomes in patients with heart failure. 
Studies also indicate that patients with SIBO had an increased risk of arterial stiffness. It is because SIBO patients have reduced absorption of vitamin K2, which is required for the activation of matrix Gla protein (MGP). Activated MGP prevents calcium accumulation in the arteries. Inadequate levels of Vitamin K2 impair the activation of MGP, and too much inactivated MGP flowing in the bloodstream is known to cause arterial stiffness and increased risk of heart disease in type 2 diabetics. [9-10]
Interestingly, the relationship between gut health and heart health appears to be a two-way street. This means coronary artery disease and atherosclerosis may also disrupt the equilibrium in the gut microbiota, possibly because of the presence of inflammatory substances.
Signs that you may have poor gut health
Digestive problems, gastrointestinal discomfort and sudden food sensitivities that were not present before could be signs that your gut health is putting your heart health at risk. What are the signs that you may have a leaky gut or poor gut health?
- Abdominal pain and distension
- Too much bloating and painful gas
- Chronic constipation or diarrhoea
- Unintentional fluctuation in your weight
- Constant and unexplained fatigue
- Sudden food allergies or food intolerances
- Skin rashes and allergies
- Sleep troubles
- Depression, anxiety and mood issues
- Headaches and migraine
- Cravings for sugar and carbohydrates
- Joint and muscle pain
- Brain fog
- Poor immunity with frequent bouts of infection
Probiotics for heart health?
With the growing understanding of how the gut microbiome may impact your heart health, taking steps to improve your gut health can be viewed as an important strategy to prevent or reduce the risk of cardiovascular disease.
Healthy modifications to your diet can go a long way in restoring the integrity of your intestinal lining and improving the diversity and function of the microorganisms residing in your gut.
This brings us to probiotics. Probiotics are friendly and helpful microorganisms that are present in your gut and are also found in certain foods and supplements. While probiotics consist of many different types of bacteria, lactobacillus and bifidobacterium are two most common probiotic bacteria. Fermented foods such as yoghurt, buttermilk, pickles, cottage cheese, miso soup, kefir can introduce probiotics in your diet. Studies suggest that some probiotics help reduce your cholesterol and blood pressure levels, especially in people with high blood pressure. [11-12]
In addition to probiotics, you can also include prebiotics in your diet. While probiotics introduce beneficial bacteria in your gut, prebiotics feed these gut bacteria. Prebiotics are dietary fibres that are not digested by the small intestine and are naturally found in foods for garlic, onion, bananas, leeks and asparagus. Prebiotics are fermented by the good bacteria in the colon and this process of fermentation lead to the production of short-chain fatty acids (SCFAs). These metabolites are considered very healthy for your body and offers a number of benefits. For example, they prevent the growth of harmful intestinal bacteria, maintain gut pH, control appetite, lower inflammation, and regulate the immune system. SCFAs also help maintain the function and integrity of your gut lining, which serves as a protective barrier between the content of your gut and the bloodstream. Damaged lining can lead to leaky gut and inflammation. Short-chain fatty acids also help in restoring the balance in the gut flora, thus proving to be helpful in gut dysbiosis.
In the past few years, there has been a lot of noise around how poor gut health may play a big role in increasing the risk of heart disease. Imbalances in the gut microbiome can lead to damaged intestinal lining or leaky gut, which in turn can cause inflammation in the blood vessels and increase the risk of atherosclerosis and coronary artery disease. The bacteria in your gut also produce certain compounds that damage your cardiovascular health. Improving the gut microbiome may hold the key to preventing or reducing this risk.
- Heianza et al. Gut Microbiota Metabolites and Risk of Major Adverse Cardiovascular Disease Events and Death: A Systematic Review and Meta-Analysis of Prospective Studies. J Am Heart Assoc. 2017
- Heianza et al. Long-Term Changes in Gut Microbial Metabolite Trimethylamine N-Oxide and Coronary Heart Disease Risk. Journal of the American College of Cardiology. 2020
- Bauer et al. Health Advantage of a Vegan Diet: Exploring the Gut Microbiota Connection. Nutrients. 2014
- Sakkaset et al. Nutritional Status and the Influence of the Vegan Diet on the Gut Microbiota and Human Health. Medicina (Kaunas). 2020
- Trefflich et al. Is a vegan or a vegetarian diet associated with the microbiota composition in the gut? Results of a new cross-sectional study and systematic review. Crit Rev Food Sci Nutr. 2020
- B Kvit et al. The role of small intestinal bacterial overgrowth in the pathogenesis of hyperlipidemia. Wiad Lek. 2019
- Fialho et al. Association Between Small Intestinal Bacterial Overgrowth by Glucose Breath Test and Coronary Artery Disease. Dig Dis Sci. 2018
- Song Y, Liu Y, Qi B, et al. Association of small intestinal bacterial overgrowth with heart failure and its prediction for short-term outcomes. J Am Heart Assoc. 2021
- Pivin et al. Inactive Matrix Gla-Protein Is Associated With Arterial Stiffness in an Adult Population-Based Study. Hypertension. 2015
- Dalmeijer et al. Matrix Gla protein species and risk of cardiovascular events in type 2 diabetic patients. Diabetes Care. 2013
- Dong et al. Effect of probiotic fermented milk on blood pressure: a meta-analysis of randomised controlled trials. Br J Nutr. 2013
- Khalesi et al. Effect of probiotics on blood pressure: a systematic review and meta-analysis of randomized, controlled trials. Hypertension. 2014