How microorganisms in your gut can impact your cholesterol levels

What is cholesterol?

Cholesterol is most commonly known as the substance which can build up in the walls of our blood vessels and contribute to the formation of blockages that cause heart attacks and strokes. This is known as atherosclerosis, and high blood cholesterol is a significant risk factor for this process and subsequent cardiovascular diseases.

However, while cholesterol can often get a bad wrap when it comes to health, it is an important lipid (or ‘fat’) that our bodies need for many crucial processes, such as:

-Synthesis of hormones, such as oestrogen, testosterone and cortisol
-Synthesis of vitamin D
-Formation and repair of cell membranes
-Production of bile salts (more on this later) (1)

Because of its important role, all of the cells in our bodies are capable of producing cholesterol but most of our cholesterol is synthesised by the liver. We can also absorb cholesterol from animal products in our diets, but this accounts for only about 30% of the total cholesterol in our body. Our bodies are also very good at holding onto the cholesterol we make and absorb from food, and there is no effective pathway for us to excrete cholesterol from our bodies. This is why some people can struggle with high cholesterol levels and, as a result, possibly develop cardiovascular disease (1).

How does cholesterol contribute to atherosclerosis and cardiovascular disease?

When your health practitioner orders blood tests to look at your cholesterol levels, they typically assess the total level of cholesterol circulating in your blood as well as the amount of cholesterol bound to particular transporter proteins (termed lipoproteins) which move cholesterol around your body. Whilst cholesterol dynamics in the body are complex, low density lipoproteins (LDL) and high density lipoproteins (HDL) are the most important.

Cholesterol bound to HDL (HDL-C) has often been termed the “good” cholesterol and cholesterol bound with LDL (LDL-C) has been labelled “bad”, but both serve necessary biological purposes. LDL delivers cholesterol from the liver to the rest of the body’s cells so that it can be used for one of the many important functions mentioned previously, while HDL carries excess cholesterol back to the liver so that it can be repurposed. When the liver is “full” and cannot take up any more cholesterol, it is sent back out into the blood bound to LDL which begins to accumulate and raises our blood cholesterol levels (1).

When levels of cholesterol (primarily bound to LDL) are elevated in the blood, this is referred to as hypercholesterolaemia (high cholesterol). High cholesterol is one of the most important risk factors for the development of atherosclerosis and cardiovascular disease, particularly coronary heart disease (CHD), heart attacks and strokes (2). High cholesterol affects approximately 39% of adults globally and is directly attributed to almost one quarter of all cardiovascular disease (CVD) related deaths. In Australia, 1 in 3 adults have high cholesterol, making abnormal cholesterol levels a major health concern.

How does the gut microbiota impact cholesterol levels in your blood?

The communities of microorganisms which live within the gut have been referred to collectively as the gut microbiota (4). The composition of our gut microbiota is inextricably linked to health and disease, with different communities of certain microorganisms being associated with an array of different disease states as well as states of good health (4). Indeed, specific gut microorganisms have been shown to be able to modify our cholesterol levels via two key mechanisms:

1. Producing bile salt hydrolase (BSH) enzymes
2. Binding to cholesterol to help excrete it from the body

Bile salts are produced in the liver from cholesterol and are the major component of bile. Bile is stored in the gallbladder and released into the digestive tract when we eat food in order to help us properly digest and absorb fats. Almost all of the bile salts in bile (and hence the cholesterol that they are made of) are reabsorbed from the digestive tract and recycled by the liver with only a small amount being lost through faeces (1).

BSH enzymes help to reduce the reabsorption of bile salts from the digestive tract, increasing their excretion through the faeces. As they are made up of mostly cholesterol, it increases the excretion of cholesterol out of the body. Consequently, the liver must compensate by pulling more cholesterol out of the blood so it can replace these lost bile salts for usual bile production (5).

Therefore, having a gut microbiota with a higher proportion of BSH-producing microorganisms may make it easier for some individuals to keep their cholesterol levels under control.

Cholesterol can also adhere to the cellular surface of some gut microorganisms, so when these bacteria are on their way out of the body (through faeces), they take the excess cholesterol with them (6).

These observations indicate that supporting the gut microbiota with specific gut microorganisms may help to support healthy cholesterol levels.

Strategies to support healthy cholesterol management

To maintain stable and healthy cholesterol levels, we know that certain healthy dietary and lifestyle habits can be of significant benefit and help to support good cardiovascular health in the long run. These habits include:

Consuming a diversity of different coloured plant foods - this helps increase fibre intake, which is known to improve LDL cholesterol and triglyceride levels (7), as well as promoting higher intake of antioxidant-rich polyphenols (i.e. berries, cacao, green tea) which are also beneficial for supporting cardiovascular health (8).

Incorporating wholefood fat sources such as olives, avocados and their oils, raw nuts and seeds, and fatty fish, rather than processed sources (commercially baked goods, deep fried foods, etc) helps support the “good” HDL-C in supporting cardiovascular health (9)

Regular exercise - at least 150 minutes per week of moderate aerobic activity (that could look like a 20-30 minute brisk walk each day), as well as at least two days a week focusing on strength / resistance training (10)

Specific probiotic strains for healthy cholesterol management

Given the promising evidence behind specific gut microorganisms in lowering high cholesterol discussed earlier, including targeted probiotic strains may also be an effective addition to the above lifestyle recommendations.

Specifically, research has shown that when a specific combination of three probiotic microorganisms (Lactobacillus plantarum KABP™ 011, L. plantarum KABP™ 012 and
L. plantarum KABP™ 013) are administered together, they can help to significantly improve the management of healthy cholesterol levels via the two mechanisms discussed earlier (6). It is important to note that not all probiotic strains possess the ability to produce BSH enzymes or bind cholesterol to their cell walls, and these strains were carefully selected because of their ability to perform these functions well. Because of these abilities, this specific combination of probiotic strains has been shown to lower LDL-C by an average of 20% in adults with high cholesterol (11, 12).

The results observed with this combination of probiotic strains is promising, particularly given the prevalence of high cholesterol. Taking a probiotic supplement to support healthy cholesterol management can be an easily achievable treatment for people, especially when incorporating new lifestyle changes can be a gradual and often challenging process.