Diet, cholesterol, and heart disease
I tweeted recently about making a new personal record as I ate altogether 7 boiled eggs in one day; three for breakfast and four with dinner consisting of salad, lentils, and salmon. Apparently this raised some questions about my cholesterol levels, and since it's been a while since I wrote anything about nutrition and health, I thought it would be a good time to clear some confusion surrounding this topic.
Coincidentally, I'm also reading Gary Taubes's Good Calories, Bad Calories and just finished a section about cholesterol. If you've read my earlier posts about nutrition and weight loss but doubt the science behind them, I really recommend getting a copy of this book. It's rather heavy to read, but gives a thorough overview about the science and research in the field of nutrition over the past 100 years. Things are not as black and white as we've been led to believe.
Most people think that cholesterol is the stuff that clogs arteries, causing heart attacks and stroke. Due to this it's also commonly believed that avoiding cholesterol rich foods such as eggs will keep you healthier. However, the truth is far more complex than that.
First of all, cholesterol is absolutely vital for life. Cholesterol molecules are the building blocks of cell membranes. Without cholesterol our cells would not be able to maintain their form. The cells in our bodies are continuously dying and born again in a cycle of life, but if we would somehow remove cholesterol the cycle would end, and so would our own existence.
In fact, cholesterol is so vitally important that only a minor portion of it is from the food we eat. Around 80% of the cholesterol in our bloodstream is synthesized by our own bodies, and in a healthy person it is a self-regulating mechanism; the more you eat cholesterol rich foods, the less your body produces it in order to maintain balance.
Now this is the point where it gets more technical, so let's get couple terms out of the way first:
Triglycerides and free fatty acids are the molecular forms in which fat is found circulating in the bloodstream.
Cholesterol is only one of several fat-like substances, which are collectively known as blood lipids.
Both cholesterol and triglycerides are transported in our blood in particles called lipoproteins, and the amount of cholesterol and triglycerides varies in each type of lipoprotein.
You may have heard about the so-called 'good' and 'bad' cholesterol, or HDL and LDL. These are actually lipoproteins that have been distributed into categories based on their densities. HDL stands for high-density lipoprotein, whereas LDL is low-density lipoprotein. A third commonly used category is VLDL, or very low-density lipoprotein.
Usually when your cholesterol is measured in a standard health checkup, it will only show the concentrations of HDL and LDL. This is not because the other particles wouldn't be physiologically important, but because more detailed measures require different equipment and are, simply put, more expensive to perform. The problem is that focusing only on LDL and HDL levels results into an oversimplification of the underlying science.
Seven different subclasses of LDL have been identified, and each of them vary in density and size. This is why heart disease sufferers may have only a few percentage points higher concentration of LDL cholesterol in average, compared to those without heart disease: the size and density of LDL particles is a more significant risk factor than the total concentration of LDL. Especially the amount of smallest and densest of LDL particles have been found to correlate with risk of heart disease much more than the overall levels of LDL cholesterol.
I understand if you find this article difficult to read and follow. I've had my own problems trying to understand these concepts, but here's something really important to take away from reading this: focusing on overall cholesterol levels will not help you stay healthy. You may even lower your 'bad' LDL cholesterol but if it means that more of it will be packaged in small, dense LDL particles your risk of heart disease will actually become higher. It also works the other way around: You may have high LDL cholesterol but when it's in the form of large, fluffy particles your heart disease risk is significantly lower.
If your doctor says you should take some form of cholesterol lowering drug, I would be adamant about getting thorough measurements of your blood lipids, not just LDL and HDL, before agreeing on any treatment.
As explained above, finding out your LDL levels will not help much in determining whether or not you have a high risk of heart disease. Luckily HDL is a somewhat better indicator: It has been discovered that HDL has a strong inverse correlation with the amount of smallest and densest of low-density lipoproteins. In other words, if you have high HDL levels - and even if your overall cholesterol is high - it would mean that most of your LDL is in the form of harmless large and fluffy particles.
Diet and cholesterol
Considering the lipoproteins, an optimal diet would increase HDL and decrease LDL, while also ensuring that the LDL in bloodstream consists of the large and fluffy particles (remember, that an increase in HDL alone can be an indicator that the LDL particle size is of the harmless kind). One of the reasons why a low-fat diet is assumed healthy is that it lowers overall cholesterol. What is left out is that in the process of doing so, a low-fat diet actually increases the amounts of smallest and densest of LDL, resulting in a higher risk of heart disease.
According to Good Calories, Bad Calories, eating an "average American diet" with 35% of calories from fat, one in three men have a risk of heart disease. When the amount of fat is increased to 46%, only one in five are in the risk group. If, on the other hand, we look at a more extreme low-fat diet with only 10% of calories from fat, the risk of heart disease becomes three times higher.
Conventional wisdom says that we should eat less fat and more complex carbohydrates. In order to stay satiated this usually means replacing the fat calories with carbs. However, it is precisely the increase in carbohydrate consumption and decrease in fat consumption that lowers both LDL and HDL, indicating a shift towards the harmful small and dense LDL particles in the bloodstream.
Fats, on the other hand, behave differently: Saturated fats raise both HDL and LDL cholesterol, monounsaturated fats both lower LDL cholesterol and raise HDL, and polyunsaturated fats lower LDL cholesterol but have no meaningful effect on HDL.
Now let's take a look at those 7 eggs I had, and meat in general: The principal fat in meat is monounsaturated and most of that is oleic acid, which is the same stuff found in olive oil. A large portion of the saturated fat is stearic acid, which increases HDL and has no effect on LDL. Lastly, a very minor portion of the fat is polyunsaturated, lowering LDL.
For example (and once again referring to Good Calories, Bad Calories), in a porterhouse steak with a quarter-inch layer of fat about 70% of it will improve the relative levels of LDL and HDL cholesterol, compared with what they would be if carbohydrates such as bread, potatoes, or pasta were consumed. The remaining 30% will raise both LDL and HDL cholesterol, having an insignificant effect, if any, on the ratio of total cholesterol to HDL.
So, I will happily enjoy my eggs in the future as well, and so should you :)