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.
This is a cholesterol molecule
This is a triglyceride molecule
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.
Read A Primer on Dietary Fats – Part 2.
Mr. McDonald, first off just wanted to add that i respect your work and always look forward to your posts. I have an honest question that I ‘m hoping you might have an incite to. One of my clients is a female that has been quite overweight since her youth. She’s not one of those who just let herself go and put on pounds. Her parents are actually quite thin yet her and her sisters are all overweight. She came to me at 340 and is currently at 295. The problem for us and the question that I have for you is that she is making a good 3-5 lbs. loss every other week and the week in between, she either stays put or even gains a pound! I change her workouts about every two weeks and I change her calories intake every so often as well. She follows a high protein, mod fat, and low carb diet which seems to be working somewhat but these weeks of zero progress are killing us. Do you have any ideas?
Lyle,
On the topic of fats, I’ve noticed that the folks from Parrillo seem to treat them as something of a bogeyman and often recommend fairly low intakes to prevent fat gain. Do you have any theories on what would precipitate such a view? It seems to fall into one of those “extreme” viewpoints, but I’d be interested in your quick thoughts on the matter.
I look forward to part II.
Thanks.
~Jack
Great article! i was just wondering what your thoughts are on the “Anabolic” style bodybuilding diet. I have been following the guidelines of this style of eating and have gains 10 lbs of muscle mass in only 5 weeks! The results for me have been amazing. Do you think that there is a problem with consuming high amounts of dietary fat and dietary cholesterol on a daily basis? Just wondering what your thoughts are.
I liked your quick treatment of the cholesterol controversy (try saying that five times fast). For people who are left wondering, there is a marginalized minority (try saying THAT five times fast) of scientists/physicians who believe serum levels of the various forms of cholesterol correlate with heart disease but are not causally involved in cardiovascular pathology. They gave some interesting ideas and theories but IMHO their credibility and objectivity is seriously impoverished by the nuts in their group that throw in the whole AMA/AHA conspiracy theories that entail this grand subversive political machine that maintains this facade due to the the profitability of treating heart disease with statins and a host of things. These are the people who rightfully belong on the fringes of academia and the clinical community who will also tell you that HIV doesn’t cause AIDS and that America has a cure for cancer but makes too much money treating the disease to release it or whatever. Yes, that makes perfect sense; it’s not that the etiological underpinnings of cancer and resultant metastasis is dictated by a set of distinct and independent physiological processes that are so complex and diverse that finding a universal cure is an exceedingly difficult and arduous task despite our best efforts. No, it’s because we don’t want to cure cancer because it keeps the population down and/or we make much more money treating it vs. curing it. I’m sure that’s it.
I really shouldn’t lump all the cholesterol dissenters into this group; many of them are rational and truly believe their lines of evidence contribute enough reasonable doubt to question the causality of blood cholesterol and heart disease, I’m just not on board with them. When the data came out that showed statin use reduced all cause cardiovascular mortality that pretty much sealed the deal for me. i dunno, it’s interesting.
Abel: Water weight does goofy things to weight loss. That’s all it is. Weight loss is rarely consistent week in week out and women moreso than men are prone to weirdness with water balance. The article i posted last week on Whooshes and Squishy Fat talks a little bit about it. As long as she’s losing that much consistently, don’t worry about it.
Jack: Parillo has long been a believer in VERY low fat diets but usually supplemented with enormous amount of MCT’s. I imagine a lot of his ideas come from the old literature suggesting that overfeeding with fat led to more fat gains than overfeeding with carbs. That’s my best guess though.
Nick: What literature exsists on the issue of blood lipids and full blown ketogenic diets (The Anabolic Diet is a cyclical ketogenic diet) suggests that as long as fat is being lost, blood lipid levels typically improve. But if it is gained or maintains, things often get much worse. I discuss what research exists in my book The Ketogenic Diet
Chris: Yeah, what you said. As I noted, I find the extremists in both camps to be a bit myopic. Clearly blood cholesterol isn’t the ONLY issue at stake for heart disease risk. Triglycerides, homocysteine, anti-oxidant levels (early research suggesting that it was only oxidized blood cholesterol that caused plaque build up) all play a role. But going from “It’s not the ONLY cause” to “It’s not a risk factor at all” is just jumping from one dumb extreme to the other.
Again, thanks for writing another great article. I just hope that more people will visit your site. There’s too many confusions going on about “cholesterol.”
How true is it that our body has a feedback loop that prevents the body from storing dietary cholesterol?