What is metabolic syndrome (MetS)?

Metabolic syndrome (MetS) refers to the combination of metabolic risk factors that can contribute to developing cardiovascular diseases, such as atherosclerosis and other metabolic disorders, including type 2 diabetes. 

The key dysregulations involved in MetS include:

• Insulin resistance: cells become less sensitive to insulin and no longer respond to it, increasing the levels of sugar in the blood
• Abdominal obesity: excessive fat around the waist and stomach
• Dyslipidaemia: abnormal levels of lipids (fat molecules) in the blood
• Hypertension: high blood pressure

What causes metabolic syndrome?

Metabolic syndrome is becoming increasingly common, often due to increasingly sedentary lifestyles and poor dietary habits. A lack of physical activity combined with unhealthy eating is a primary cause for metabolic syndrome. Diets consisting of ultra-processed foods or foods high in sugar are linked to obesity and can therefore cause MetS.¹

On the other hand, there are genetic predispositions which may cause MetS, such as having a family history of diabetes, cardiovascular diseases or hypertension. Additionally, certain populations, such as South Asians, are at a higher risk of developing MetS and other metabolic complications, even without obesity.¹

What is dyslipidaemia?

Dyslipidaemia refers to an abnormal level of lipids (fats) in the blood. There are four classes of fat that circulate within the body:

• Triglycerides: a type of fat found in the blood and stored in the body. Triglycerides are a major source and storage form for energy, contributing to insulation and protection in the body and for vital organs
• LDL (low-density lipoprotein): known as the ‘bad cholesterol’. It is a particle made up of lipids and proteins and carries cholesterol from the liver to other tissues to produce hormones and carry out other metabolic processes
• HDL (high-density lipoprotein): known as the ‘good cholesterol’, as it helps to protect against cardiovascular disease by collecting excess cholesterol from tissues and transporting it back to the liver for removal
• VLDL (very low-density lipoprotein): a type of lipoprotein which transports triglycerides from the liver to other tissues for energy and storage. VLDL is then converted into LDL, which can deposit cholesterol in places such as the arteries, damaging cardiovascular health

Dyslipidaemia involves high levels of triglycerides, LDLs and overall cholesterol, which is deposited in various tissues and the arteries. Excess fat can build up in the arteries and form plaques if the fat is not removed. HDL cholesterol is often in low concentrations in dyslipidaemia, which prevents effective removal of fat from the organs and blood vessels. This can contribute to cardiovascular diseases such as atherosclerosis, as fat builds up in the arteries.²

Arteries clogged with fatty plaques are incredibly dangerous to our health as they prevent adequate blood flow. As the red blood cells carry oxygen, blood needs to be able to flow through the arteries to reach the heart and other tissues. If there is plaque blocking the artery, this can prevent oxygenated blood from reaching the heart, causing heart attacks and can stop blood flow to the brain, leading to a stroke.²

How is dyslipidaemia caused?

There are various mechanisms causing dyslipidaemia in MetS. Insulin resistance is a key driver of dyslipidaemia in metabolic syndrome. This is because insulin normally works to store fat and suppress the breakdown of fatty tissue. When insulin resistance occurs, and the body is no longer responsive to insulin, fatty tissue does not respond to insulin and is not stored, which leads to the breakdown of fat and the release of free fatty acids (FFAs) into the bloodstream. Free fatty acids are then taken up by the liver to form triglycerides.³

Triglycerides can be packaged into VLDLs in order to transport cholesterol. When the liver is resistant to insulin, this causes an overproduction of VLDL, releasing too many free fatty acids into the blood.³

These fatty acids then circulate in the blood and can penetrate the arterial walls, becoming oxidised and forming plaques within the artery.

In metabolic syndrome and obesity, adipose (fatty) tissue can become dysregulated. Fatty tissue cells are more likely to become resistant to insulin and release more free fatty acids into the bloodstream. They also alter the amount of hormones they secrete; for example, they decrease the secretion of adiponectin, which causes inflammation and increased appetite. Enlarged fat cells can trigger inflammation and release cytokines to enhance insulin resistance.

Diagnosing dyslipidaemia

Clinical evaluation

Clinical evaluations are the first step to diagnosing dyslipidaemia in MetS. Medical professionals typically assess if a patient has a family history of cardiovascular disease or lipid disorders, as well as a personal history of obesity, diabetes and high blood pressure. A consultation (and physical examination, for obesity) about lifestyle and dietary habits is also necessary, as diet, physical exercise, alcohol and smoking all have an impact on MetS.^4,5

Fasting lipid profiles

Fasting lipid profiles measure lipids in the blood. This is done 8-12 hours after fasting (not eating or drinking) to avoid increases in triglyceride fats from recent meals. The factors measured are:

• Total cholesterol: A high total cholesterol would suggest a higher risk of atherosclerosis, as it combines all the cholesterol in lipoprotein molecules
• LDL: Elevated LDL suggests dyslipidaemia could be occurring and promotes plaque formation and CVD
• HDL: In cases of dyslipidaemia, HDL would be low, as it suggests that no cholesterol or fat is being removed from the blood
• Triglycerides: High triglyceride concentrations are common in metabolic syndrome and dyslipidaemia⁴

Diagnostic criteria

Dyslipidaemia is generally confirmed if the results show:

• High triglycerides: >1.7 mmol/L
• Low HDL: <1.0 mmol/L in men and <1.3 mmol/L in women
• High LDL: >3.0 mmol/L 
• High non-HDL: >1.1 mmol/L⁴

Treating dyslipidaemia

Lifestyle modifications

The first line of treatment for dyslipidaemia associated with MetS is a lifestyle intervention. This includes limiting alcohol, stopping smoking and making changes to your diet, such as reducing the intake of trans and saturated fats in order to lower LDL cholesterol. Increasing consumption of unsaturated fats (including foods such as nuts, fish and olive oil) will help to improve the lipid profile, as well as eating high fibre fruits, vegetables and whole grains. Limiting simple sugars and refined carbs will help to reduce triglycerides. These changes in your diet can prevent the accumulation of fat in the blood and help to avoid plaque formation in the arteries and body tissues.

Physical activity is key to treating dyslipidaemia. Physical activity and weight loss can improve the level of triglycerides and HDL in the body, as well as maintain insulin sensitivity in your cells. This causes less fat breakdown and fat release into the blood. Those suffering from dyslipidaemia should aim to complete approximately 150 minutes of moderate exercise a week.⁵

Pharmacological treatment

If lifestyle changes are not enough to treat dyslipidaemia, or if cardiovascular risk is too high, there are various pharmacological treatment options. Statins are the first line of drugs used as they reduce LDL levels and triglyceride levels to stabilise plaque build-up. Statins can be combined with fibrates, which decrease high triglycerides.⁴

Vitamin B3 and omega-3 fatty acids can also be taken in order to raise HDL levels and lower triglyceride levels. They are also, less commonly, used if there are side effects with statins and fibrates.⁴

Summary

Dyslipidaemia is a key driver of metabolic syndrome, a combination of conditions including abdominal obesity, insulin resistance and hypertension. It is characterised by high levels of triglycerides and LDL cholesterol and low levels of HDL cholesterol. The primary cause of dyslipidaemia is insulin resistance, which inhibits insulin's ability to prevent lipid breakdown in fatty tissues. This leads to the release of free fatty acids into the bloodstream. Free fatty acids are absorbed by the liver, overstimulating the liver to produce lots of VLDL cholesterol. This causes overall dysfunctional adipose (fatty tissue) through altered hormone secretion and chronic inflammation.

Dyslipidaemia can cause cardiovascular disease by promoting atherosclerosis. This is because the dysregulated fats can build up in the blood vessels and penetrate arterial walls, becoming oxidised and hardening into plaques. And due to the lack of HDL in the blood, there is no cholesterol removal from these plaques. These plaques can therefore block blood supply to the heart and prevent the efficient transport of oxygen, causing complications such as myocardial infarctions and strokes.

Diagnosis includes producing a fasting lipid profile to measure various types of cholesterol and their amounts in the body. Prevention is also crucial, and is central to lifestyle changes such as keeping a healthy diet, losing weight, exercising regularly and limiting alcohol and smoking. Drugs can also be taken alongside this, including statins, fibrates, omega-3 fatty acids and vitamin B3. 

FAQs

What is dyslipidaemia?

Dyslipidaemia is a condition in which there are abnormally high levels of lipids (fats) in the blood. This consists of high triglycerides and LDL cholesterol, as well as lowered HDL cholesterol.

What is the link between dyslipidaemia and metabolic syndrome?

In metabolic syndrome, there are various dysregulations in metabolism, such as insulin resistance and adipose (fat) tissue dysfunction. These conditions can disrupt the metabolism of fats in the body, causing a high amount of fat to be released into the blood (dyslipidaemia).

How does dyslipidaemia cause cardiovascular disease?

The high fat content in the blood can penetrate blood vessel walls. Fat can then deposit inside the blood vessels (mainly arteries) and harden over time, forming plaques. As these fatty plaques grow, they can block blood flow in the arteries, and this is known as atherosclerosis. In dyslipidaemia, there are low concentrations of HDL cholesterol, and this prevents the removal of fat from the arteries.

How is dyslipidaemia diagnosed?

A fasting lipid profile measures the total cholesterol, HDL, LDL and triglyceride fats in the body. 

Can dyslipidaemia be prevented?

Yes. Changes in lifestyle are key to avoiding dyslipidaemia and metabolic syndrome. Altering your diet to reduce sugar and processed foods (in order to manage insulin resistance), regular exercise to manage weight and reducing alcohol intake and smoking can help prevent dyslipidaemia. 

How is dyslipidaemia treated?

Treatment includes medications such as statins (which lower LDL cholesterol), fibrates (lower triglycerides) and omega-3 fatty acids. Addressing insulin resistance also improves lipid profiles.