Cholesterol, Triglycerides and Heart Health
Part of the Metabolic Health blog series
If you have ever had a blood test that flagged your cholesterol, you will probably recognise the unease that comes from being given a number without much explanation. You may have been told that your LDL is too high, your HDL is too low, or that your triglycerides need watching. Perhaps you have been advised to eat less fat or red meat, or to consider taking a statin, and you are left trying to understand what any of it actually means for your health.
Cholesterol is one of the most commonly discussed markers in cardiovascular health, but it is also one of the most misunderstood. There is more to your cholesterol result than the total number on your blood test. This article looks at what the different parts of a lipid panel actually measure, why they matter, and what the evidence tells us about using diet to improve them.
What Is Cholesterol, and Why Does the Body Need It?
Cholesterol is a waxy, fat-like substance found in every cell of the body. It plays several essential roles, including maintaining cell membranes, producing steroid hormones such as oestrogen, testosterone, and cortisol, and making bile acids, which are needed to digest and absorb dietary fat.
Most of the cholesterol in your body is made by the liver, typically around 75 to 80 percent, with the remainder coming from food (1).
Because cholesterol is a type of fat, it cannot travel freely through the bloodstream, which is water-based. Instead, it is packaged into transport particles called lipoproteins. These carry cholesterol and triglycerides through the circulation to the tissues where they are needed.
Understanding Your Lipid Panel
A standard lipid panel usually measures four things: total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. Looking at these values together gives a much more useful picture than focusing on total cholesterol alone.
LDL cholesterol
Low-density lipoprotein, or LDL, is often referred to as the 'bad' cholesterol. LDL particles carry cholesterol from the liver to the tissues that need it. The problem arises when there are too many LDL particles circulating in the blood. They can enter the walls of arteries, where they contribute to inflammation and the formation of fatty plaques, a process known as atherosclerosis (2).
The relationship between LDL cholesterol and cardiovascular risk is one of the most well-established findings in cardiovascular medicine. Large-scale genetic and clinical studies have consistently shown that lower exposure to LDL is associated with a lower risk of cardiovascular events (3).
For people without established cardiovascular disease, an LDL cholesterol level below 3.0 mmol/L is considered the target in the UK, although the target will be lower for people at higher cardiovascular risk. For those at high risk, a level below 1.8 mmol/L is commonly recommended (4).
HDL cholesterol
High-density lipoprotein, or HDL, is often described as the 'good' cholesterol. HDL particles help transport cholesterol away from tissues and back to the liver, where it can be processed and removed from the body.
Higher HDL levels are generally associated with lower cardiovascular risk, while low HDL is one of the five criteria used to identify metabolic syndrome, as discussed in the first article in this series.
There is an important distinction here, however. Although low HDL is associated with increased cardiovascular risk, simply raising HDL does not necessarily reduce that risk. This suggests that the function of HDL particles may matter as much as the amount present in the blood (5).
Rather than trying to raise HDL in isolation, the focus should therefore be on the wider pattern: eating a minimally processed diet, reducing refined carbohydrates and added sugars, being physically active, and avoiding smoking.
Triglycerides
Triglycerides are the main form in which fat is stored and transported around the body. After eating, the liver packages excess energy into triglycerides and releases them into the bloodstream, partly through particles called very-low-density lipoproteins, or VLDL.
High triglyceride levels, generally above 1.7 mmol/L, are associated with increased cardiovascular risk. They also commonly occur alongside low HDL and a higher proportion of small, dense LDL particles, forming part of the wider pattern seen in metabolic syndrome (6).
Triglycerides are also one of the lipid markers most responsive to dietary and lifestyle changes. Reducing added sugars, refined carbohydrates, and excess alcohol can be particularly helpful, as can improving insulin sensitivity through regular physical activity and a healthier overall diet.
This is one reason triglycerides can provide useful information about metabolic health. Chronically elevated insulin can increase the liver's production of triglycerides, which helps explain why high triglycerides so often appear alongside elevated blood sugar and low HDL.
Why the total cholesterol number can be misleading
This is why it is important not to focus too heavily on total cholesterol in isolation. Two people can have the same total cholesterol number but very different lipid profiles and, therefore, very different levels of cardiovascular risk.
For example, a higher total cholesterol result driven by relatively high HDL, with low LDL and triglycerides, tells a very different story from the same total cholesterol result driven by high LDL and elevated triglycerides.
If your GP has flagged your cholesterol, it is therefore worth asking which parts of the lipid panel are contributing to the result. Looking at LDL, HDL and triglycerides together gives a much more useful picture of what is actually going on.
How Diet Influences Cholesterol and Triglycerides
This is where things become particularly interesting, especially if you grew up being told that dietary fat is the main cause of high cholesterol. The evidence is more nuanced than that. Different types of fat, carbohydrate, fibre, and dietary cholesterol affect the lipid profile in different ways.
Saturated fat and LDL
The relationship between saturated fat and LDL cholesterol is well established. Saturated fat, found primarily in fatty meat, full-fat dairy, butter, coconut oil, and palm oil, can raise LDL cholesterol by reducing the liver's ability to clear LDL from the bloodstream (7).
What matters, however, is what replaces the saturated fat. A 2020 meta-analysis of 35 randomised controlled trials, published in the Journal of the American Heart Association, found that replacing saturated fat with unsaturated fat significantly reduced LDL cholesterol and improved the total cholesterol to HDL ratio (8).
Trans fats have an even more unfavourable effect, raising LDL while lowering HDL. They were largely removed from the UK food supply following regulatory action, although small amounts can still be found in some imported and ultra-processed foods.
Unsaturated fats and cardiovascular risk
Replacing saturated fat with unsaturated fats generally improves the lipid profile. Monounsaturated fats, found in foods such as olive oil, avocados, and nuts, can modestly reduce LDL cholesterol without lowering HDL.
Polyunsaturated fats, particularly those found in nuts, seeds, and plant oils, tend to produce a greater reduction in LDL. Randomised trial data also suggest that replacing saturated fat with polyunsaturated fat can reduce cardiovascular events (9).
Omega-3 fatty acids are another important part of the picture. Alpha-linolenic acid (ALA) is found in foods such as flaxseed, chia seeds, hemp seeds, and walnuts. Omega-3 fats have particularly strong evidence for reducing triglycerides, although the effects differ between plant-derived ALA and the EPA and DHA found in marine sources.
For people following a fully plant-based diet, this is worth considering when planning sources of omega-3 fats and, where appropriate, discussing with a practitioner.
Dietary cholesterol
Dietary cholesterol, found in foods such as eggs, shellfish, and organ meats, generally has a smaller effect on blood cholesterol than the type and amount of fat in the diet. This is partly because the liver adjusts its own cholesterol production in response to how much cholesterol is absorbed from food.
The response does vary between individuals, however, and some people experience a more pronounced rise in LDL cholesterol when they consume more dietary cholesterol. Overall, the evidence suggests that, when considering cardiovascular risk, the type of fat eaten alongside dietary cholesterol may matter more than the cholesterol itself (10).
Fibre and plant sterols
Soluble fibre is one of the most consistently supported dietary interventions for lowering LDL cholesterol. It binds to bile acids in the digestive tract and reduces their reabsorption. As a result, the liver needs to use more cholesterol to make new bile acids, helping to remove LDL cholesterol from the bloodstream.
Good sources include oats and barley, which are rich in beta-glucan, as well as legumes, psyllium husk, apples, and flaxseed. A 2014 meta-analysis of 28 randomised controlled trials found that beta-glucan from oats reduced LDL cholesterol by an average of 0.25 mmol/L, a modest but clinically meaningful reduction that can be achieved through food alone (11).
Plant sterols and stanols work in a different way. They compete with cholesterol for absorption in the small intestine, reducing the amount that enters the bloodstream. Intakes of around 1.5 to 3 g per day have been shown to reduce LDL cholesterol by approximately 7 to 12 percent (12).
Refined carbohydrates, sugar, and triglycerides
The quality of the carbohydrate in your diet can have a substantial effect on triglycerides. Diets high in refined carbohydrates and added sugars can increase the liver's production of triglycerides, partly through the effects of elevated insulin.
Replacing refined carbohydrates with whole-food sources such as intact grains, legumes, and vegetables can therefore help reduce fasting triglycerides, in some cases more effectively than simply reducing total fat intake (13).
This is particularly relevant when triglycerides are elevated alongside high blood sugar or insulin resistance, as these markers often form part of the same wider pattern of metabolic dysfunction.
The Case for a Whole Food Plant-Based Diet
A diet built around whole plant foods can address several of these lipid risk factors at the same time. It naturally provides more fibre and plant sterols, while generally being lower in saturated fat and higher in unsaturated fats.
A 2017 systematic review and meta-analysis published in JAMA Internal Medicine, which pooled data from 49 randomised controlled trials involving more than 7,000 participants, found that vegetarian dietary patterns were associated with lower total cholesterol, LDL cholesterol, and non-HDL cholesterol compared with omnivorous diets (14).
The potential benefit comes from the overall dietary pattern rather than from any single food or nutrient. Replacing foods high in saturated fat with whole plant foods can reduce LDL cholesterol, while the higher fibre content can provide an additional benefit. Legumes, whole grains, nuts, seeds, vegetables, and fruit also provide a wide range of other compounds that contribute to overall cardiovascular health.
It is also worth noting that a very low-fat plant-based diet is not necessarily the best approach for every lipid marker. If fat is replaced largely with refined carbohydrates and added sugars, triglycerides can rise and HDL can fall. The quality of the carbohydrate matters, too.
This is why the focus should be on a whole food plant-based diet, rather than simply a low-fat or meat-free diet. Intact grains, legumes, vegetables, fruit, nuts, and seeds provide a very different nutritional profile from a diet based around refined flour, sugar, and highly processed plant-based foods.
What This Looks Like in Practice
So, what does this mean when it comes to what you actually eat? The dietary changes with the strongest evidence are relatively straightforward:
Choose unsaturated fats more often. Replacing foods high in saturated fat, such as fatty meat and full-fat dairy, with sources of unsaturated fat such as extra virgin olive oil, nuts, seeds, and avocado can help reduce LDL cholesterol without necessarily lowering HDL.
Include oats or barley regularly. Even a modest daily portion provides beta-glucan, a type of soluble fibre that can help lower LDL cholesterol when eaten consistently over time.
Make legumes a regular part of your meals. Beans, lentils, and chickpeas provide soluble fibre, plant protein, and carbohydrate that is digested more slowly. Including them regularly can support both LDL and triglyceride control.
Keep added sugars and refined carbohydrates to a minimum. If triglycerides are elevated, reducing foods and drinks high in added sugars and refined carbohydrates can be particularly helpful.
Don't overlook physical activity. Regular aerobic exercise can help raise HDL and reduce triglycerides, and it works alongside dietary changes rather than replacing them.
A Note on Statins and Medication
For people with significantly elevated LDL cholesterol, established cardiovascular disease, or a high calculated cardiovascular risk, statin therapy is well supported by clinical evidence and can substantially reduce the risk of cardiovascular events.
Dietary change remains an important part of the picture, but it does not replace a conversation with your GP. Many people see meaningful improvements in their lipid profile when they make consistent changes to their diet and lifestyle, and these changes can form an important part of a wider approach to cardiovascular risk reduction.
If you are already taking a statin or other cholesterol-lowering medication, don't reduce or stop it without speaking to your GP or prescribing clinician first. If your cholesterol improves as a result of dietary and lifestyle changes, your treatment can be reviewed with your healthcare professional where appropriate.
Next in the series is Blood Sugar and Insulin Resistance looks at the spectrum from optimal blood sugar to type 2 diabetes, how the body loses and regains insulin sensitivity, and what dietary patterns the evidence supports most consistently.
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References
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