What role does food play in maintaining cholesterol levels?
It has been well documented in both scientific literature and in the media that high cholesterol is problematic for our health, with it being strongly linked to worsening cardiovascular health due to the development of atherosclerosis (build-up of arterial plaque) and the increased risk of heart attacks and strokes.
The NHS suggests that a healthy individual should have a total blood cholesterol of less than 5mmol/L, with less than 4mmol/L recommended for those at high risk.
How does cholesterol get high?
Cholesterol is transported around the body by proteins, which are known as lipoproteins. The two main types of lipoprotein are; high-density lipoprotein (HDL) which transports cholesterol to the liver to either be broken down or excreted, and low-density lipoprotein (LDL) which normally transports cholesterol to cells.
When LDL levels are high and HDL levels are low, excessive amounts of cholesterol gets deposited in artery walls.
Food is usually the first place to start when it comes to addressing cholesterol levels so let’s take a closer look at some dietary influences of cholesterol.
Consumption of fat, and in particular saturated fat is shown to increase LDL cholesterol, but also increase HDL to a lesser extent. Trans fats have a larger harmful effect by also causing a reduction in HDL cholesterol, and therefore negatively affect the ratio of good to bad cholesterol. This is important as HDL is responsible for clearing LDL and helps to prevent arterial build up. A large reduction in LDL cholesterol can be achieved by replacing saturated fat with monounsaturated or polyunsaturated fats.
Monounsaturated fats are found in avocados, olive oil, and nuts.
Omega 3 and Omega 6 are both types of polyunsaturated fatty acids that you must get from your diet. A great source of Omega 3 is oily fish, (Salmon or Mackerel), it's also found in walnuts, chia seeds and linseeds. Omega 6 is found in corn oil and sunflower oil which is rich in lineloic acid. Both Omega 3 and Omega 6 play a crucial role in healthy functioning of the body and both can lower LDL.
A healthy diet, however, contains a balance of Omega 3 and Omega 6 fatty acids. Omega 3 helps to reduce inflammation, whereas some Omega 6 fatty acids can promote inflammation. The typical western diet contains 16 times more Omega 6, than Omega 3.
The Mediterranean diet has a much healthier ratio of Omega 3 and Omega 6 which is one of the most well-studied diets for its prevention of noncommunicable diseases and reduced risk of premature mortality. A landmark trial in the study of the Mediterranean diet, the PREDIMED trial, concluded a significant inverse association with CVD incidence.
Meat and Dairy
There is a very strong link between saturated fat found in meat products and increased LDL cholesterol, with research suggesting replacement with soya products to prevent this.
The impact of dairy on cholesterol is much more contentious, as the majority of observational studies do not show an association between the intake of saturated fat from dairy and cardiovascular disease. Intervention studies propose that this is due to an increase in both LDL and HDL cholesterol, resulting in the ratio remaining unchanged.
The beneficial effects of fibre are wide-ranging, particularly in relation to gut health. Though insoluble fibre is not shown to have any effect on cholesterol, soluble fibres can have a positive effect.
You've most likely seen the health claim on oat packaging promoting a reduced risk of heart disease; this is due to a soluble fibre found in them called beta-glucan or oat gum. The evidence suggests 1g per day of beta-glucan can lower LDL cholesterol, so incorporating oats into your diet is a good way to help keep your cholesterol at a healthy level.
Plant Sterols and Stanols
Plant sterols and stanols are compounds found naturally in plants and are structurally very similar to cholesterol. The two compete for absorption, resulting in reduced absorption of cholesterol.
The cholesterol-lowering effects of these compounds have been shown to be greater than simply avoiding foods high in cholesterol. Interestingly, they are not currently recommended by NICE guidelines for those with high cholesterol, which is likely due to the fact that there are no studies showing that consumption of plant stanols or sterols results in reduced cardiovascular risk.
What does it all mean?
Whilst individual dietary components undoubtedly influence cholesterol in both positive and negative ways, nutrition research is increasingly pointing to the importance of overall diet quality rather than individual dietary elements.
This was demonstrated in the Young Finns Study one of largest follow up studies of CVD risk from childhood to adulthood, which concluded that long-term adherence to a traditional Finnish diet, high in rye, potatoes, butter, sausages, coffee, and milk, was associated with increased arterial narrowing.
Similarly, a study analysing the current UK dietary guidelines assessed men and women aged between 40 – 70 years old without cardiovascular disease, and showed that when adhered to over 3 months, following the guidelines can result in a significant reduction in LDL cholesterol.
For those looking to reduce cholesterol through diet, making several dietary changes is likely to have a significant and meaningful effect.
It is advised to reduce consumption of processed foods and added sugar, and shift towards cardio-protective nutrients such as fibre found in vegetables and whole grains and healthy fats found in nuts, seeds and olive oil and fish.