Do you know which foods contain good cholesterol, and which contain bad cholesterol? If you think you do, ha! That's a trick question! Cholesterol in our food doesn't come in "good" and "bad" varieties, but cholesterol readings from blood tests do, and the two aren't as closely connected as we used to think.
Illustration: Sam Woolley
What Is Cholesterol, Really?
We make cholesterol in our bodies. It's a key part of cell membranes, and we use it as a building block to make important chemicals like hormones, vitamin D and bile.
Other animals make cholesterol too, so you'll find it in animal foods like meat, dairy and eggs. Since cholesterol is a lipid (it mixes well with oil, but not with water) you'll tend to find it in the fatty parts of food. But it's not a type of fat!
Plants don't make cholesterol, so anything vegan (like vegetable oil) is automatically cholesterol-free.
More importantly, since we make our own cholesterol, the amount we eat isn't very important. Cholesterol, while important in our bodies, is not essential in our diet. If you never eat another cholesterol again in your life (hi, vegans!) your body will still make plenty and do just fine.
In fact, we make far more cholesterol than we eat (even if you're a devoted carnivore). The liver adjusts its cholesterol production to account for what we eat, and will get rid of any cholesterol it doesn't need, so even if you eat a ton of cholesterol, it will have little to no effect on what's in your blood.
Food Cholesterol Is Different From Blood Cholesterol
Some folks confuse fat with cholesterol. There are good and bad fats, but the cholesterol you eat has no such distinction. When it's sitting on your plate, it's just plain cholesterol. It only becomes "good" or "bad" when it's packaged into particles in your bloodstream.
Those good and bad packages are lipoproteins: little particles that transport fat and cholesterol to specific destinations in your body. The low-density lipoproteins, or LDLs, are considered bad because people who have a lot of them are more likely to develop heart disease. The LDLs can get stuck in the walls of arteries, in a process that leads to atherosclerosis, the hardening of the arteries that can lead to heart attacks and stroke.
high-density lipoproteins, or HDLs, help remove the LDL particles to avoid forming plaques. So it's good to have a lot of HDLs (think H for "happy") and bad to have a lot of LDLs.
What Those Blood Tests Mean
Here's where the blood tests come in. Decades ago, all we could measure was total cholesterol in a blood sample. That number turned out to be pretty useless. What really matters is the number of HDL and LDL particles (and perhaps some other details like the size of those particles), but we have to stick with what's easiest to measure.
So when you get a blood lipid test done, the numbers include total cholesterol, HDL cholesterol (that is, the amount of cholesterol that was being carried around in HDL particles), and triglycerides. From those numbers, the lab can calculate how much cholesterol was probably in your LDL particles. These HDL-cholesterol and LDL-cholesterol numbers give you a clue about how likely you are to be developing atherosclerosis that could lead to a heart attack.
According to the most recent guidelines for doctors, you can figure out your risk of a future heart attack with a few facts: your cholesterol readings, your blood pressure, and whether you're a smoker or have diabetes (which increase your risk). That and your age, race, and sex will lead to an ominous prediction of your percentage chance of having a heart attack in the next ten years.
If the risk is over 7.5 per cent, according to the guidelines, your doctor should talk to you about taking a statin medication, which lowers LDL cholesterol and has been shown to prevent recurring heart attacks in people who have already had one before.
Cholesterol-altering medications are controversial. Even though statins work to prevent second heart attacks, they have little to no benefit for people who never had one before. And other types of cholesterol-altering medications, like niacin (which raises HDL), don't reduce heart attacks in real-world use. This suggests that statins may not work by lowering LDL in the blood, but by some other mechanism that just happens to lower LDL as a side effect.
Meanwhile, statins have some nasty side effects, including muscle pain that can make exercise unpleasant or impossible — and exercise is important for reducing your risk of heart disease. So if your cholesterol numbers aren't looking good, plan on a thoughtful talk with your doctor about the risks and benefits of medication.
What You Eat Does Affect Your Blood Cholesterol — But Not How You Think
The cholesterol we eat has little to no effect on the cholesterol or lipoproteins in our body — for most of us, anyway. (Some experts are recommending that people with diabetes still go easy on the eggs.)
Otherwise, a heart-healthy diet will improve your LDL and HDL numbers regardless of the amount of cholesterol that passes through your lips. Opinions vary — this is nutrition, after all — but you'll always do right to stick with the three things everybody agrees on: don't eat trans fats, eat less sugar and get plenty of veggies.
After that, you can follow the standard advice: Eat less saturated fat and more soluble fibre to reduce LDL. Get exercise and eat plenty of omega-3 fatty acids (found in fish and nuts) to raise HDL. Triglycerides aren't a type of cholesterol, but they do seem to raise your heart disease risk and you can lower them by avoiding sugar and refined carbs.
The DASH diet is a classic eating plan that accomplishes those goals (while also keeping blood pressure low for people who are salt-sensitive). The Mediterranean diet is another good option. And you can always put the above advice to work by modifying your regular diet to include more fruits, veggies and whole grains.