A Primer on Dietary Fats – Part 1
For the past 30 years or so, ever since people started talking about cholesterol and heart disease, there has been a combination of concern and confusion over the topic of dietary fats in the diet. In this article, I want to take a look at some of the topics involved to see if I can help to clear up some of the confusion.
Today I want to look at some general issues, including the major categories of dietary fats, the difference between cholesterol and triglycerides, and then look briefly at the impact of dietary cholesterol on blood cholesterol levels. On Friday, in Part 2, I’ll look in some detail at the different types of dietary triglycerides and address some of the current controversy over their effects on health.
Triglycerides, Cholesterol and Everything Else
While people tend to throw around the term dietary fat somewhat loosely, the fact is that not all of the fat that we consume on a daily basis is the same. And here I’m not talking about saturated vs. unsaturated fats. Quite in fact, dietary fats (more generally known as lipids) come in distinct chemical types.
Now, the primary two that folks eat on a day to day basis are triglycerides (TGs) and dietary cholesterol with dietary triglyceride contributing the bulk (over 90% of the total) of the dietary fat that we consume on a day to day basis.
However, there is also a small amount of lipid that come from sources such as various phospholipids and other fat based compounds; since they tend to make up a very small percentage of the total daily fat intake, I’m not going to spend any time discussing them.
Rather, I want to focus primarily on dietary triglyceride and cholesterol.
For completeness, I should note that there are also dietary diglycerides (two fatty acids bound to a glycerol molecule) which may have some slight fat loss benefits. In the Ultimate Diet 2.0, I mentioned Enova Oil (which is apparently no longer being produced), a diglyceride oil that can increase fat loss slightly over the length of a diet. Dietary diglycerides may also be a bit more filling in the short-term (compared to dietary triglycerides) due to how they are processed in the body; this may also give them some benefit for dieting.
For true completeness, there has also been some recent interest in the use of free fatty acids in terms of appetite control, although I’ve yet to see a commercial product that contained them. In any case, the primary source of dietary fat in the diet will be dietary triglycerides with cholesterol playing a secondary role.
Triglycerides and Cholesterol: What’s the Difference?
For several decades now, many people have been confused about dietary triglyceride versus dietary cholesterol, with many seeming to think that they are identical or at least related.
The confusion most likely stems from the extreme focus on blood cholesterol and heart disease risk that really started in the late 1970′s and 1980′s. Since many of the foods that people were becoming concerned with (e.g. ‘high-fat’ meat or eggs) tend to contain a lot of dietary cholesterol as well, people seemed to link the two substances in their minds.
And while it’s true that high-fat animal foods are generally also high in cholesterol, this isn’t always the case; some low-fat foods (such as certain types of shellfish) can actually be high in cholesterol despite being low in total fat content. However, in general, high-fat animal foods tend to be high in cholesterol as well and I suspect this is where much of the confusion about the two stems from.
But structurally and chemically, dietary fats and cholesterol couldn’t be more different.
Cholesterol is what is termed a steroid molecule. It has a complex ring like structure and one of it’s main functions in the body is as a precursor molecule for other compounds with a similar structure (such as testosterone, cortisol, estrogen, progesterone and others).
In contrast, the dietary fats that make up the majority of our daily intake are more accurately called triglycerides (or tri-acyl-glycerols if you want to be fancy). They have a chemical structure where three fatty acid chains (‘tri’ = three) are bound to a molecule of glycerol (which is where the ‘glyceride’ part of the name comes from).
You can see the chemical structure of both dietary cholesterol (left hand picture) and a triglyceride molecule (right hand picture) below.
As you can see, they are nothing alike chemically or structurally. And, as I’ll discuss, they have completely different effects in the body.
Of Dietary Cholesterol and Blood Cholesterol
As I mentioned above, I think that part of the confusion over dietary fat and cholesterol came out of the focus on blood cholesterol levels and heart disease that really got rolling in the 70′s and continued well into the 80′s. And when that was combined with the fact that many of the ‘off-limit’ high-fat foods (such as eggs) were also high in dietary cholesterol, it’s actually easy to see where the confusion comes from.
Now I’m actually not going to get into the big debate/argument/controversy over the role of blood cholesterol in heart disease. Sufficed to say that I think both groups of extremists, both those that think blood cholesterol is the primary concern as well as those who think it is no concern at all are misguided; I find this is true of most extremist stances. At best, I think blood cholesterol levels are one of several factors that contribute to the development or not of heart disease; but there are certainly others. I’ll leave the topic at that.
In any case, what is often forgotten is that the body actually makes more cholesterol (in the liver) than most people would eat in a day. As well, the body tend to adapt to changing dietary cholesterol intakes. When you eat less dietary cholesterol, the body will make more; when you eat more, the body makes less.
And this is why a lot of the concern over dietary cholesterol per se is a bit misplaced; for most people the intake of dietary cholesterol has little to no impact on blood cholesterol on the first place. It’s worth mentioning that a certain percentage of people seem to be responders to dietary cholesterol intake in terms of how their blood cholesterol is affected.
Rather, it is the intake of specific types of triglycerides that seems to have a far larger role on blood cholesterol levels; exercise also plays a role and there are strong genetic factors which determine blood cholesterol levels as well.
But since that discussion of different types of dietary triglycerides is going to be fairly long, I’m going to save it for Part 2 which I’ll post on Friday.