What you need to know about LDL cholesterol (and what to do about it)

We are living in a fast paced era – hectic lifestyles, speedy transport, fast food, new technology coming out at an unbelievable rate, tons of news and information bombarding us every day. The same goes for the science on human nutrition.

30 or 40 years ago, health authorities thought that fat was to blame for increasing waistlines. Over the following decades, sugar became the culprit. Now, some believe that the enemy is carbohydrates and that fat is actually good for us – both unsaturated (the ‘good’ form) and saturated fat (the ‘bad’ form)! Or at least, that saturated fat derived from fatty meat, full cream dairy, and highly processed food does not have the negative impact on our heart and arteries that we previously thought it did. This is backed up by some very good quality meta-analysis studies and systematic reviews (meta-analysis and systematic reviews are journal articles that analyse multiple large-scale, good quality studies and tries to draw a conclusion from them).

When I studied nutrition and dietetics at The University of Sydney 10 years ago, we were educated that all types of saturated fat are unhealthy for us. So should we disregard the previous nutritional advice and start eating tons of saturated fat? How can we cope with this new but conflicting information? The intention of this article is not to completely solve this big issue, but to present some suggestions based on the current level of nutritional science on saturated fat in 2020. Before we begin, a commonly used term needs to be explained – cholesterol.

What is cholesterol? 

Basically, cholesterol is essential for all of us. It is a waxy, fat-like substance made by our livers. We need cholesterol to help our brain, skin and other organs do their jobs. It allows our bodies to make vitamin D and different hormones. It also exists in the membrane of every single cell in our body.

So, knowing that we all need cholesterol, how come you always hear from your doctors that you need to reduce your cholesterol when it is high? It’s because there is a range of healthy cholesterol levels. If the level gets too high, you are more likely to develop heart disease. At least, that is what we used to think. That’s why there is always a range for normal cholesterol levels. Both too high and too low are not good for us. 

There are a few different types of cholesterols: 

HDL (High-density lipoprotein): this type of cholesterol is also known as “good” cholesterol. It picks up excess cholesterol from our blood and carries it back to the liver, where they are broken down. Most of the health experts and doctors, as well as old and recent studies agree with this conclusion. We are not going to focus on this in this article. 

LDL (Low-density lipoprotein): this type of cholesterol is commonly known as “bad” cholesterol. This is where you get conflicting information. Some claim that LDL cholesterol is bad, while on the other hand, new research indicates that LDL has no connection with heart disease and mortality which goes against the previous study results1. Both of them have been strongly supported. 

In 1986, Anderson KM and et al2 studied cholesterol and mortality in the famous Framingham heart study. Basically, they followed participants for up to 30 years and found that cholesterol levels are directly related with 30-year overall and cardiovascular disease mortality. In 2007, Prospective Studies Collaboration published an article in Lancet including almost 900,000 adults and found a similar result3. Moreover, moderate lifelong reduction in LDL is associated with a substantial reduction in the incidence of coronary events according to Jonathan C and et al4. 

On the other side of the argument, Ravnskov Uffe and et al in 2016 investigated 16 cohort studies including a total of 68,094 elderly people (over 60 years old) and found that high LDL is inversely associated with mortality in most people over 60 years. And interestingly, Anderson KM and et al2 in the same study did find that after the age of 50 year, the association of mortality with cholesterol is confounded, which is quite different to the population from the 30-50 year old group.

Wait a minute. How can this be possible? If both sides hold good evidence, what is the truth? For people with this question, we must use a different angle to look at it.

So, what goes wrong?

Let’s examine LDL a bit deeper. LDL derives from VLDL (very low density lipoprotein). LDL is a complex particle called lipoprotein, which carries cargo. Part of the cargo it carries is cholesterol. Normal LDL sits nice and quite in our bodies without causing trouble to our bodies and eventually is recycled by our liver and removed from our circulation. The problem starts when LDL is damaged or oxidized and the structure of LDL changes to oxidized-LDL. It cannot be recycled from our liver anymore and starts sticking to the wall of our blood vessels and gradually thickens and blocks our blood vessels, eventually causing coronary heart disease due to blocked arteries.

What damages the LDL?

The simple answer is excessive amounts of carbohydrate, that is, more than our bodies need, and refined carbohydrates including added sugar. Too much of the above makes the LDL undergo a process called glycation. This means the sugar molecules start attaching to the LDL. When this happens, it changes how the LDL functions. It cannot be recycled from our liver anymore. It gradually accumulates in our blood and will be swallowed by our macrophage cells, which then become foam cells5 and thicken the wall of our blood vessels. Atherosclerosis starts from here6. Oxidized low-density lipoprotein becomes a strong predictor for coronary heart disease7,8. 

To put it simply, you could understand it like this:

• Saturated fat makes your LDL become high.

• Excessive amounts of carbohydrate (more than our bodies need) and refined carbohydrates including added sugar makes your LDL turn bad.

How do you know if your LDL has been oxidized? 

Well, that’s when triglyceride comes in. If you have a close look at your cholesterol blood test, you will find triglyceride in the Lipids section. Elevated triglycerides are predominantly affected by eating excessive amounts of carbohydrate, as well as refined carbohydrates including added sugar. Precisely the prerequisite for the LDL to be oxidized! From my own clinical experience, high triglycerides are also a good indication of the onset of insulin resistance (pre-stage diabetes). They often go hand in hand.

What’s the real problem in our lives?

When you get up, a carton of chilled sweetened iced coffee is needed for good refreshment. In the morning, you might get bored and feel peckish, so you go and grab a donut. You are so busy at work, a Western style Chinese takeaway fits perfectly into your schedule. At the end of the day, you quickly go home, chuck a few meat pies and French Fries in the oven and dinner is done for the whole family. You are exhausted after the whole day and just want to sit in front of the TV and spend the whole evening with your soul mate – chocolate. Tomorrow will be the same. 

You may laugh. Modern lifestyles often look like this. As you can see, a lot of everyday foods have both refined carbs and are high in saturated fat. This is where the problem lies.

Where to from here?

I consider LDL a silent danger. Yes, the studies above show that normal LDL causes almost no harm to us even when it is elevated; however, once LDL is oxidized, it causes all sorts of severe problems. And the foods that we eat which cause the LDL oxidation are so common that many people eat them every day. 

Here’s my suggestions:

1. Reduce excessive amounts of carbohydrates and refined carbohydrates including added sugar to prevent LDL from getting oxidized;

2. Decrease our blood LDL by cutting back on the saturated fat from highly processed food and add more unsaturated fat into our diets including nuts, olive oil, salmon and avocado so that less LDL is oxidised.

Technology and science are moving forward at a rate like never before. New research might come out again and again. Our current practice might be improved or overruled. It is always challenging for us to be ready and to adapt constantly. Adopting a prudent and adaptable attitude towards these questions is always a good way to go.

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References:

1. Ravnskov, U et al, Lack of an association or an inverse association between low-density-lipoprotein cholesterol and mortality in the elderly: a systematic review. BMJ Open, 2016, Vol. 6, No. 6, doi:10.1136/bmjopen-2015-010401.

2. Anderson, KM, et al. Cholesterol and mortality. 30 years of follow-up from the Framingham study. JAMA, 1987, Vol. 257, No. 16, pp 2176-80.

3. Prospective Studies Collaboration, et al. Blood cholesterol and vascular mortality by age, sex, and blood pressure: a meta-analysis of individual data from 61 prospective studies with 55,000 vascular deaths.

4. Jonathan, C, et al. Sequence Variations in PCSK9, Low LDL, and Protection against Coronary Heart Disease. N Engl J Med, 2006, Vol. 354, pp. 1264-72. DOI: 10.1056/NEJMoa054013

5. Laszlo, N, et al. Oxidized LDL Regulates Macrophage Gene Expression through Ligand Activation of PPARγ, Cell, Vol. 93, No. 2, Apr 1998, pp. 229-40.

6. Giuseppe, M, et al. The Role of Oxidized Low-Density Lipoproteins in Atherosclerosis: The Myths and the Facts. Hindawi, 2013, Article 714653, doi.org/10.1155/2013/714653

7. Holvoet, P, et al. Circulating oxidized LDL is a useful marker for identifying patients with coronary artery disease. Arterioscler Thromb Vasc Biol, 2001, Vol. 21, No. 5, pp 844-8.

8. Meisinger, C, et al. Plasma oxidized low-density lipoprotein, a strong predictor for acute coronary heart disease events in apparently healthy, middle-aged men from the general population. Circulation, 2005, Vol. 112, No. 5, pp 651-7.