What actually causes high cholesterol? - Hei Man Chan

In 1968, the American Heart Association made an announcement that would influence people’s diets for decades: they recommended that people avoid eating more than three eggs a week. Their reasoning was that the cholesterol packed into egg yolks could increase cardiovascular disease risk. But it turns out that the reality is more complicated.

Let's delve into digestion to understand why. As your body processes a meal, it emulsifies fats into lipid droplets that can then get absorbed in your small intestine. These lipid droplets make their way to various tissues, including your liver.

There, specialized cells unpack and reassemble them into lipid-protein packages, called lipoproteins, that are optimized to flow through your bloodstream. Lipoproteins are composed of different ratios of protein and fat, so their density varies. VLDL, or very low-density lipoprotein, is mostly packed with fatty molecules, including triglycerides and cholesterol.

VLDL delivers lipids to your muscle and fat cells to be stored and used for energy. Afterwards, it’s converted into LDL, or low-density lipoprotein. LDL is informally known as “bad cholesterol” because it’s associated with cardiovascular diseases.

This is because LDL is more prone to accumulating on blood vessel walls, which can cause inflammation. The inflammation attracts specialized white blood cells, called macrophages, to remove the LDL buildup. But absorbing too many lipids can compromise macrophages, causing more inflammation and triggering more macrophage recruitment.

As the cells clump together, they form a fibrous, scab-like cap, effectively narrowing the artery. This can interfere with blood flow and weaken vessel walls, making clots and ruptures more likely. High-density lipoprotein.

or HDL, on the other hand, packs more protein. It picks up excess LDL in the blood and brings it back to the liver, where it can be excreted. Because HDL is anti-inflammatory and keeps LDL in check, it’s commonly called “good cholesterol.

” Doctors order lipid panels to understand the concentrations of different kinds of lipoproteins and their building blocks in your blood. All lipoproteins are essential to your body’s functioning— but it can become a problem if the different kinds get out of balance. Some people are simply predisposed to having higher cholesterol.

For example, certain gene variants cause LDL receptors to behave abnormally, leaving more LDL circulating. Otherwise, different lifestyle factors can influence blood lipid levels. And food is one of them.

So, what’s the deal with eggs? Their yolks are indeed high in cholesterol, which prompted the American Heart Association’s three egg weekly limit in 1968. But while some of the cholesterol in your blood comes directly from cholesterol found in food, your body actually makes a vast majority of it from the different fats you consume.

Saturated and trans fats, found in animal, palm, and coconut products can drive your liver to create more VLDL and LDL packages. Unsaturated fats, meanwhile, are abundant in foods like fish, nuts, and seeds, and have anti-inflammatory properties that help counteract LDL buildup. A food’s fat composition has a greater effect on blood lipid concentrations than its cholesterol levels.

So the high cholesterol found in egg yolks isn’t actually of too much concern. Egg yolks contain some saturated fat, but not too much— and they also contain unsaturated fats. Generally, an egg a day is considered nutritious.

But it's not just what fats you eat, but what you eat them with. Fibrous fruits, vegetables, and whole grains help lower LDL levels by affecting how fats are absorbed in the digestive tract. Overall, getting plenty of unsaturated fats and fiber seems to help keep LDL in check.

And other activities can also impact lipid levels. It's not yet totally clear why, but resistance training and aerobic exercise can lower LDL and increase HDL. This might be because they use more blood lipids for energy and boost the activity of HDL-producing enzymes.

Meanwhile, smoking increases LDL buildup, perhaps by unleashing unstable free radical molecules that damage lipids and vessel walls. But when lifestyle changes don’t help to manage cholesterol levels, as can be the case when genetics are at play, we luckily have some pretty effective therapies. Statins are drugs that block a liver enzyme required to produce LDL.

Other cholesterol medications increase the production of enzymes that break down triglycerides and promote LDL receptor activity, helping clear it from the bloodstream. When it comes to cholesterol health, it’s important to keep the whole picture in mind— on and off the plate— so things don't get all, you know, scrambled.