Today I want to finish up by looking at more detail at the issue of dietary triglycerides.  As I mentioned in Part 1, dietary triglycerides (TGs) make up the bulk of the fat that we consume in a day, providing over 90% of our total fat intake.  Therefore, understanding what the different ‘types’ of TG are along with how they affect the body is important.

Types of Dietary Triglyceride

As I mentioned in A Primer on Dietary Fats – Part 1, a fat/TG molecule consists of three fatty acid chains bound to a backbone molecule of glycerol.  And while people tend to talk about different types of fats (e.g. saturated fat or unsaturated fat), it’s actually the specific fatty acids that differ in terms of their chemical structure.  For simplicity, I’ll simply refer to the different types of ‘fats’ and leave it at that.

Things such as chain length, degree of saturation and chemical conformation all go into distinguishing one fat from another but I’ll try to avoid boring people with that level of detail.  Fats are pretty much universally subdivided into four primary categories which are

1. Trans-Fat
2. Monounsaturated Fat
3. Saturated Fat
4. Polyunsaturated fat

And there’s no reason for me to go against that grain.  Below, I want to look briefly at each type of fat, where it’s found in the diet, what types of effects it has on the body, and address any of the lingering controversies that currently exist.

Trans Fat

Since there is little to no debate or controversy over the role of trans-fatty acids (often abbreviated TFAs) in human health, I figured I’d tackle it first.  In recent years, it’s fairly safe to say that trans-fatty acids (aka partially hydrogenated vegetable oils) have gotten the most press in terms of their negative health effects.   And there is much truth to this.

Trans-fatty acids are a semi-solid fat which are made by bubbling hydrogen through vegetable oil (hence the name partially hydrogenated vegetable oil).  This is done to make vegetable oils (which can often be unstable and go rancid) more shelf-stable; that’s important when foods sit on the shelf for a long time.   Margarine is a classic example that most will be familiar with, a semi-solid made by bubbling hydrogen through vegetable oil.

And while there are naturally occurring trans-fatty acids that occur in small amounts in foods, quantitatively most of the trans-fats that people will consume will come from the intake of processed foods.

The problem is that the process of partial hydrogenation changes the chemical structure of the vegetable oil from what is called a cis-configuration (the form that most dietary fatty acid are found in) to a trans-form.  Hence the name trans-fatty acid.  Without going into a lot of unnecessary details, simply accept that the body is meant to use cis-fatty acids, not trans-fatty acids; it’s got to do with the chemical shape of the fatty acid.

For that reason, intake of a large amount of trans-fatty acids causes a number of problems in the body.

Quoting from a a recent review on the metabolic effects of trans-fatty acids:

TFA [trans-fatty acid] consumption causes metabolic dysfunction: it adversely affects circulating lipid levels, triggers systemic inflammation, induces endothelial dysfunction, and, according to some studies, increases visceral adiposity, body weight, and insulin resistance…Consistent with these adverse physiological effects, consumption of even small amounts of TFAs (2% of total energy intake) is consistently associated with a markedly increased incidence of coronary heart disease.

Now, I’m rarely a fan of nutritional absolutes but this is one place where I’m willing to make one: trans-fatty acids really have no place in human nutrition and this is a place where there is little disagreement in the field.  They provide absolutely no benefits that I’m aware of and their impact on human health would appear to be wholly negative.

Monounsaturated Fat

If there is another fat over which there is really no argument or controversy in the field it’s monounsaturated fat.  At worst, monounsaturated fats are fairly neutral from a health perspective (especially in terms of the effects on blood cholesterol levels) and there is also evidence that intake of monounsaturated fats may have health benefits.

Quite in fact, it’s thought that part of the benefit of various Mediterranean diets is related to the large intake of olive oil (arguably the primary dietary monounsaturated fat) in the diet.  It’s certainly worth mentioning that other aspects of their diet such as a large vegetable/anti-oxidant intake is assuredly contributing to the good health observed; that is, it’s not just the olive oil.

In any case, outside of being a source of calories (excessive calories causing fat gain, of course), there’s no real indication that mono-unsaturated fats have any real negatives in terms of human health.

The primary mono-unsaturated fat is oleic acid which is found in very high amounts in olive oil (hence the name).  It’s worth noting that oleic acid actually tend to be the primary fatty acid found in most ‘high-fat’ foods (you can check this for yourself at the USDA database) including the ones that most think of as containing large amounts of saturated fat.  A couple of examples appear in the table below.

Because of it’s prevalence in the food supply, olive oil will often make up a fairly large proportion of someones total dietary fat content without much effort.  However, when people are looking to ‘add fat’ to their diet (for whatever reason), it would be hard for them to go wrong in using a source of mono-unsaturated fat or Olive oil.  It can be added to salads and I know of some brave souls who throw it directly into protein drinks when they need to raise calories.

I’d mention that, for people (like me) who don’t like the taste of olive oil, there is a high oleic safflower oil available for people who want to add more oleic acid to their diet.

Saturated Fat

For a couple of decades now, saturated fat has been the veritable whipping boy of the nutritional world (forced out of the number one position by trans-fatty acids only recently).  Blamed for everything in the world including heart disease and probably terrorism, saturated fats have received the brunt of negative press when it comes to the issue of dietary fats.

However, in recent years, there has been a counterargument regarding saturated fat intake that they are of no health risk at all, that the real problem is with excessive polyunsaturated fatty acids/vegetable oils (discussed next), etc.

This has led to a lot of confusion for people.

Now, anybody who has regularly read this site knows that I tend to shy away from nutritional extremism, I usually find that whenever there are competing extremist positions, the truth generally lies somewhere in the middle.

This is certainly the case for saturated fat in my opinion.  Now, for anybody who reads nutritional research, there is little to no argument that saturated fat can cause a variety of problems. Whether you’re looking at blood lipid levels, inflammation, etc. there’s really little debate in the field and there are a zillion and one studies that support that excessive saturated fat intake can cause a variety of health problems.

However, as always it gets more complicated.

A a huge part of the problem is that the term saturated fats actually refers to a category that includes a number of different fatty acids.  Lauric acid, palmitic acid, stearic acid and many others are all included under the general heading of saturated fat.

And at least part of the problem is that they don’t all act the same way in the body.  Some specific saturated fatty acids have distinctly negative effects on the body, others do not.  For anybody truly interested in the science of this topic, I’d recommend the paper Saturated Fats: What Dietary Intake which examines the issue in some detail.

As well, as I have discussed in other articles on this site such as Carbohydrate and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2, I think there is a huge issue of context in terms of the effect of saturated fat (or any nutrient for that matter) on overall health.

For someone who is lean, active, eating plenty of fruits and vegetables, who is in caloric balance there appears to be no real danger (in a health context) to an increased intake of saturated fats.  One study I recall in cyclists found that, as long as they were in caloric balance, an increase intake of saturated fats had no impact on blood cholesterol one way or the other.

It’s worth mentioning in this context that some research suggests that saturated fat is required for optimal hormone levels (e.g. testosterone) so trying to reduce saturated fat excessively may be a mistake for athletes in the first place.

But not all individuals are lean, active athletes who are eating lots of fruits and vegetables who are in caloric balance.  For someone who is overweight (which is an inflammatory state in and of itself), inactive (which has a host of negative health effects), is under a lot of stress, not eating sufficient fruits and vegetables, etc. , saturated fats may have a very different impact on the body.

There is often also an impact of weight loss or weight gain in terms of how saturated fats affect blood lipid levels; in general when weight is lost, blood cholesterol levels improve almost irrespective of the type of fat consumed. But when weight is being gained or even maintained, often blood cholesterol levels worsen with a high saturated fat intake.

I should mention that the changes that typically occur in blood cholesterol levels with changing saturated fat intake tend to occur in both the ‘good’ and ‘bad’ cholesterol fractions.  That is, when saturated fat is reduced, both good and bad cholesterol typically goes down and vice versa.  Therefore the overall impact on health risk is a bit more complex than many think.

In any case, I think that saying that saturated fats are good, bad or neutral is too simplistic.  Context, as always, is important and I find that many of the extremists in each group tend to forget that.  What is drastically unhealthy in one context may be neutral or at least irrelevant in another.  Which still won’t stop some very silly comments from appearing on this article as people accuse me of being ‘anti-saturated fat’.

In any case, finishing up, saturated fats are found more or less exclusively in animal source products and are typically solid at room temperature.  A couple of odd exceptions are coconut and palm kernel oil (both of which contain a lot of saturated fat but primarily in the form of medium chain triglycerides, discussed below).  As well, milk fat contains a decent amount of saturated fat.

From a body fat perspective, it’s at least worth mentioning that saturated fats tend to be stored a bit more easily than polyunsaturated fats (more accurately, when polyunsaturated fats are consumed, the body tends to burn them off a bit more readily) but the effect is not massive.

Polyunsaturated Fat

And finally we come to polyunsaturated fats.  Almost always liquid at room temperature (unless found in foods), the key polyunsaturated fats are the omega-3 and omega-6 fatty acids (which you’ll often see referred to as w-3/w-6 or n-3/n-6).   This naming simply refers to the structure of the individual fatty acid and it’s not worth going into any more details than that.

The two primary polyunsaturated fats are alpha-linolenic acid (ALA, not to be confused with the supplement alpha-lipoic acid) which is an w-3 fatty acid and linoleic acid (LA) which is an w-6 fatty acid.  Among other things, ALA and LA have the distinction of being the two essential fatty acids (EFAs), that is it is essential that they be obtained from the diet for optimal health.  This is in contrast to all of the other types of fat discussed, none of which is actually essential for life or health.

Strictly speaking, you could live forever if you never consumed another gram of saturated, monounsaturated or trans fat.  But a long enough deficiency of either ALA or LA would eventually cause a host of health problems and eventually death.  It’s worth mentioning that it takes the absolutely most artificial of diets (usually completely fat free diets served in a hospital setting) to generate a true ALA or LA deficiency; even the worst diet will tend to cover bare minimum requirements of both.  In fact, it took years of research to even determine that there were essential fatty acids because causing a true deficiency was so difficult.

When saturated fats started to become ‘the enemy’ in the 70′s and 80′s, there was a big push for an increased intake of vegetable oils in the diet.  That is, if people were going to eat a lot of fat, it was thought that eating more vegetable oils would be better than saturated fats.

As always, things are not quite so simple and, as I noted above, some groups think that the increased intake of vegetable oils is actually the cause of many health problems blamed on saturated fats.

Ok, now everybody is really confused, let me see if I can unconfuse things.

Both ALA and LA turn out to have a massive number of effects in the body ranging from modulating gene expression, producing or inhibiting inflammation and a host of others; they are also involved in the production of eicosanoids, short-lived chemical signalling molecules that do a zillion different things in the body. It’s worth mentioning that many of these effects are mediated by compounds formed by the metabolism of ALA and LA within the body.

That is, ALA and LA are sort of ‘parent compounds’ for other things in the body.  For example, LA is converted to gamma-linoleic acid which may have anti-inflammatory effects (and many women swear helps with PMS).  LA is also converted to arachidonic acid (AA) which is an inflammatory compound that may be involved in muscle growth.  ALA undergoes extensive metabolism and can be converted to EPA and DHA (the fish oils, I’ll spare you the full names) which I’ll come back to below.

Of more importance, although both are essential fatty acids, ALA and LA often have different and frequently opposing effects; in general, the effects of the w-3 fatty acids tend to be ‘good’ and the effects of w-6 are ‘bad’ although, as always it’s far more complex than that.

This is important because there has been concern regarding the modern diet that the ratio of w-6:w-3 fatty acids is causing a variety of health problems.

For example, it’s thought that our evolutionary diet had a ratio of w-6:w-3 intake of between 1:1 and 4:1; the modern diet contains somewhere around 20-25:1.  This skewed ratio is due both to the abundance of w-6 in the food supply as well as the exceeding lack of w-3 fatty acids in the modern diet.  Because of this, finding ways to boost the w-3 content of foods (such as high w-3 eggs) is a huge area of research.

And it’s been argued that this skewed ratio is contributing to a myriad of health problems, not the least of which is inflammation and increased heart disease risk (with an increased intake of w-6 being blamed for the problem).  Current research calls this into question, however.

Quoting from a recent review titled “Too much linoleic acid promotes inflammation, doesn’t it?” by Kevin Fritsche

Existing evidence in humans, though limited, fails to show a link between higher dietary LA intake, or higher plasma LA, and greater inflammation in vivo. In fact, some of the data suggest the opposite may be true [my note: he's saying that increased LA intake may be ant-inflammatory].

Quoting from another paper titled “The role of dietary n-6 fatty acids in the prevention of cardiovascular disease.” by Walter Willett:

Because n-6 fatty acids are the precursors of proinflammatory eicosanoids, higher intakes have been suggested to be detrimental, and the ratio of n-6 to n-3 fatty acids has been suggested by some to be particularly important. However, this hypothesis is based on minimal evidence, and in humans higher intakes of n-6 fatty acids have not been associated with elevated levels of inflammatory markers…In the United States, for example, intake of n-6 fatty acids doubled and coronary heart disease (CHD) mortality fell by 50% over a period of several decades. In a series of relatively small, older randomized trials, in which intakes of polyunsaturated fat were increased (even up to 20% of calories), rates of CHD were generally reduced.

Basically, a lot of the concern over high w-6:w-3 ratios may be misplaced but I’m not going to get into the debate beyond that.

For the most part, I don’t think worrying about w-6 intake is much of an issue.  On even the most moderate fat diet, w-6 intake will be generally be more than sufficient and trying to consume more is rarely necessary.  Whether or not intakes need to be explicitly reduced and what impact that will actually have is something to let the nutrition researchers argue about for the time being.

Rather I want to focus on the w-3 fatty acids about which there is far less debate; at this point about a zillion studies (+-a million) have shown benefits of increased w-3 intake on a myriad of health parameters.  Decreased inflammation, improved blood lipid levels (including decreased triglyceride levels), decreased risk of heart disease, decreased depression and even fat loss have all been found from w-3 supplementation.

Now, recall from above that both w-3 and w-6 fatty acids undergo significant processing in the body with ALA being converted downstream to EPA and DHA, at least potentially.  It’s EPA and DHA that I want to talk about now.

Readers are probably more familiar with EPA and DHA as fish oils since that is how they are typically referred to.  As you might expect, both compounds are found in large amounts in fatty fish (free range animals often have a larger proportion of w-3 fatty acids as well).

Quite in fact, the original interest in fish oils came from the observation that cultures (such as the Alaskan Inuit) had low rates of heart disease despite a ‘high-fat’ intake.  It turned out that the large intake of fish oils were a huge part of that.

And while ALA is still technically considered the ‘essential fatty acid’, it’s looking more and more like it’s actually the EPA and DHA that are doing the majority of the ‘good’ things in the body (and that they may do different things in the body meaning that they are both important).  Whether ALA actually does anything indepdently of its conversion to EPA/DHA is currently being debated.

And here’s why this is a problem: outside of vegetarians/vegans, the conversion of ALA to EPA/DHA is extremely small in adults.  When ALA is supplemented (for example, from flax oil), the actual conversion to EPA is only about 4-5%.  And the conversion of EPA to DHA is negligible; that is, supplementing the parent compound doesn’t raise body stores of DHA at all (in fact, supplementing with EPA doesn’t raise DHA either).

This topic is discussed in some detail in the research review Extremely Limited Synthesis of Long Chain Polyunsaturates in Adults: Implications for Their Dietary Essentiality and Use as Supplements.

But the point holds, simply ensuring sufficient intake of ALA (e.g. from flax or another vegetable oil) does not ensure that there will be a significant increase in EPA or DHA which appear to be the key fats in terms of improving health; in fact it’s almost certain that it won’t raise EPA/DHA sufficiently to be of benefit.  In my opinion, the only way to ensure adequate EPA/DHA intake is by ensuring a daily intake from preformed sources.

For people who consume fatty fish (or perhaps free range meat) on a regular basis, that is generally an adequate source.  For everyone else, supplementing with either pills or liquids will generally be necessary to ensure a sufficient daily intake.

And, as I stated in the research review I linked to above, while w-3 fortified foods are becoming available, I find that they are not cost effective; rather than buying high w-3 eggs, it’s far cheaper to buy normal eggs and take an w-3 supplement.

I’m not going to get into dosing issues here since that’s really beyond what I wanted to talk about in this article; I’ll address that at a later date.  An absolute bare minimum would be a combined intake of EPA/DHA of 500mg per day.  A standard 1 gram fish oil capsule typically contains 180 mg EPA and 120 mg DHA (300 mg of total fish oil) so that would be only 2 pills per day. There is evidence that more may be beneficial for a variety of goals but, again, I’ll save that discussion for a later article.

Summing Up

So what started out as a primer on dietary fats got a little bit longer than I had intended.  Hopefully now you understand the difference between dietary cholesterol and triglycerides along with understanding what the different types of dietary triglycerides are and what roles they might or might not have in the body.  I’ve also tried to address some of the current confusion and controversy that currently exists over the different types of fats.

I also realize that I didn’t address much in the way of practical recommendations.  Frankly, assuming folks are consuming a moderate fat diet (perhaps 20-25% of their total calories), outside of ensuring that they get sufficient amounts of EPA/DHA on a daily basis and mostly avoid trans fat intake, I’m not sure it’s worth being that concerned with.

Most ‘high-fat’ foods contain a mix of saturated and monounsaturated fats and ensuring sufficient w-6 intake is rarely an issue unless dietary fat intake is kept extremely low for long periods or the diet is very artificially set up.

It’s usually w-3 fatty acids that are lacking in most diets and ensuring their intake will do most of the good in my opinion.  As noted up above, if an athlete needed to consciously add more fat calories (for example an endurance athlete who can’t meet their caloric needs), a separate source of monounsaturated fats would be the first choice.

I also realize that didn’t talk extensively about Enova Oil or speciality oils like Medium Chain Triglycerides (MCT’s).  That will have to wait for a later article.

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.

A: A fairly standard dose of fish oil in the studies is the equivalent of 6X1 gram capsules. The average capsule has 180 mg epa and 120 dha so 6 capsules will provide 1020 mg epa and 720mg dha for a total of 1.8 grams of total fish oil. I would consider this basically the minimum daily amount that would be beneficial on any level.

Some work has identified that the body will hit a limit (in terms of plasma saturation) on DHA at 1.2 grams per day which is the equivalent of 10X1 gram fish oil capsules. That would also provide 1.8 grams EPA for a total of 3 grams per day of fish oil. Under most conditions, I think this is more than enough.

A friend who uses fish oiils to control her arthritis will often go as high as 15X1 gram capsules although I haven’t seen that supported in the literature. I’d note that higher doses are not better here (although some are currently recommending absurd amounts). Excessive fish oil can impair the body’s ability to mount a proper immune response, as well as impairing insulin release.

Carlson’s fish oil contains roughly the equivalent of 4X1 gram fish oil capsules per tsp., I don’t know the values on cod liver oil offhand.

My current generic recommendation is the middle level, 10X1 gram capsules per day for 3 grams total fish oil. This should provide maximal benefits (in terms of partitioning and health) with minimum negatives. Individuals trying to control a specific excessive inflammatory condition may wish to experiment with higher doses (15X1 grams capsules or 3-4 tsp Carlson’s fish oil per day).

Examining Both Sides of the Debate

As noted, the usual argument goes that high-fat diets cause high-cholesterol, heart disease, cancer, obesity and the rest, as evidenced by the high incidence of those disease in modern diets (which are typically high in fat). But that’s a questionable conclusion to draw.

Modern diets are also high in carbohydrates (and mainly the highly refined, high GI, low-fiber stuff that the body often doesn’t handle well), low in fruits and vegetables, and generally contain the wrong types of fats (an excess of saturated and trans fats with insufficient amounts of healthy fats). Such an intake is typically coupled with inactivity, the folks eating them tend to be overweight/obese, smoking and alcohol play a role, etc. That is, there are a number of inter-related factors at work here.

Pinning the blame entirely on fat intake or expecting only a reduction in fat to fix the problem is disingenuous: there are a lot of variables at work here. Some research suggests that the entirety of the problem rests with excessive saturated fat intake with the other variables (activity, fruits and vegetables, etc.) playing a relatively minor role. It’s awfully hard to tease out all of the relationships when there are this many variables at play.

Similar comments can be made in terms of obesity. Fat is more calorically dense than carbohydrates and studies comparing high-fat (40%) to low-fat (25%) meals find that people tend to eat more in the higher fat conditions; this is usually referred to as passive over-consumption and leads to excess calorie intake. These studies have problems, mind you, but that’s beyond the scope of this article. The point does stand, though, that dietary fat is tasty (giving food mouth feel) and folks do tend to eat more of foods that taste good.

But while it’s common to blame obesity on high-fat diets, not all researchers agree. Some cultures have fairly high fat intakes but have no problems with obesity and researchers are starting to realize that fat isn’t the ONLY problem. Increasing intakes of refined carbohydrates (contributing large numbers of calories to the diet), decreasing activity, increasing portion sizes and other factors all contribute. You can’t dismiss an excessive fat intake as part of the obesity problem; it’s simply not the sole factor. I don’t want to get into a massive discussion of the carb versus fat debate in terms of caloric intake, preferring to focus on the health issues here.

The fact is that not all studies link a high fat intake to an increased risk of disease. For example, recent analyses of our ancestral diet (what we ate during 99.9% of our evolution) suggests a much higher fat intake and much lower daily carbohydrate intake. Exact numbers vary depending on what assumptions you use but carb intakes of 20-40% (most of which came from low GI, high fiber fruits and vegetables; grains were almost non-existent), fat intakes of 28-60% (which had a significantly different quality than our current diet), and protein intakes of 19-35% of total calories are the current best estimates.

Studies of extant hunter-gatherer societies show little incidence of any of the diseases of modern society and it’s thought that our evolutionary diet was NOT atherogenic (promoting heart disease) despite the high fat intake.

The reasons for this are many-fold, of course and that’s the key to keep in mind when you consider fat intakes and potential health problems. In our ancestral diet, fiber intakes were monstrous, averaging 100-150 grams per day. As well, despite the high fat intake, the source of that fat was far, far different than our modern intake. Much higher intakes of polyunsaturated and mono-unsaturated fats and far lower intakes of saturated fat were fairly typical. Activity levels were also much higher and folks generally stayed pretty lean. Alcohol intake was low or non-existent, as was smoking. Although our ancestors dealt with various stresses, they didn’t deal with the kinds of chronic stress that occurs in modern societies.

Related to this, studies of the Mediterranean diet have found few problems in terms of heart disease and all the rest despite a relatively high fat intake (40% of total calories). Although the reasons are, as always, multi-factorial some of the contributing factors are that the fat intake is primarily from mono-unsaturated sources (e.g. olive oil).

As well, a tremendous amount of fresh vegetables are typically consumed (with far less reliance on refined carbohydrates). Other factors such as activity, bodyweight, moderate alcohol intake and lowered stress levels probably play a role. Studies of the Alaskan Inuit show similar results, despite an extremely high-fat intake, heart disease is almost unheard of. This has typically been attributed to the high intake of fish oils but there may be genetic adaptations as well.

Of course, some studies on low-carbohydrates diets (which are typically high in fat) will show a big improvement in blood lipid levels; this is especially true for individuals with insulin resistance. I’d note that this effect primarily occurs when weight is lost; in studies of very low-carbohydrate diets where weight is gained, blood lipid levels often get much much worse.

Thus, whether or not you’re gaining or losing weight probably impacts on whether or not dietary fat is a health risk. I’d note that studies in cyclists find that high intakes of saturated fat don’t pose a health problem as long as the athletes are in calorie balance. As I mentioned above, activity (which will affect whether ingested dietary fat is stored or burned off) plays a big role here.

Studies in diabetics are finding that higher mono-unsaturated fat intakes (and lowered carbohydrate) intakes may be healthier than the converse. This, of course, only holds if calories are strictly monitored and controlled to avoid weight gain. When weight is gained, from nearly any dietary approach, blood sugar control in diabetics worsens.

Of course, there’s a flip side to the anti-fat dogma and reducing fat to extreme levels can cause its own set of problems. First and foremost, most people find extremely low-fat diets to be tasteless and this tends to limit adherence in the long-term (as I mentioned above, high-fat diets tend to be very tasty and people frequently eat too much).

And while caloric intake typically goes down in the short-term, folks frequently end up increasing caloric intake because they are hungry all the time. Dietary fat slows gastric emptying (keeping food in the gut longer) although some work suggests that this effect is lost with chronically high-fat diets. Extremely low-fat diets tend to leave people hungrier for this reason.

There is also evidence that the fat-soluble vitamin absorption may be impaired when fat intake is taken too low. And while total cholesterol typically decreases when fat intake is lowered, the decrease occurs in both the good (HDL) and bad (LDL) sub-fractions so overall health risk may not be improved. From a body recomposition or performance standpoint, some studies show a lowering of testosterone with very low fat diets.

There is another set of issues that crops up as well. Again, it relates to the simple fact that people have to eat something. In reducing fat intake, most people increase carbohydrate intake. Most researchers would say that this is just fine as long as the increase comes in the form of unrefined, high fiber, complex carbohydrates. I would say that most researchers need to get out of the lab and look at the real world for a while.

The simple fact is that the majority of people who reduce fat do NOT increase carbohydrate intake from unrefined, high-fiber, complex sources. This is especially apparent in the US (I can’t speak for other countries) where companies rapidly jumped on the ‘fat is bad’ bandwagon and brought tons of ‘low-fat’ high-carbohydrate sources that were highly refined to market.

Such foods may have as many, if not more, calories than the same higher-fat items. Even when they don’t, humans play a cute psychological game, tending to eat more of a given food when they are told it’s low or no-fat.

Recent studies are finding that, when carbs are increased from those sources, other problems show up. In addition to the changes in blood cholesterol I mentioned above (both the good and bad subfraction decrease), the increase in refined carbohydrate intake causes an increase in blood triglyceride levels and small LDL particles; both of which are independent risk factors for heart disease and all the rest. The chronically high insulin levels which commonly occur with such a diet cause other problems including insulin resistance and all of the issues that accompany it.

I should probably note, and this could certainly be an entirely separate article, that the new scapegoat for obesity and all of the health problems in the world is excessive carbohydrate intake, with a lot of the focus on insulin release. I don’t have space here to address that side of the argument, a future topic for another day.

Sufficed to say that while there is certainly an element of truth to this (in that excessive intakes of any nutrient, and that includes refined carbohydrates, is bad), it’s still true that simplistically arguing that ‘fat is good and carbs are bad’ is just as moronic as arguing that ‘carbs are good and fat is bad’. Again, it depends on the context.

Summing Up

Now, I want to make it very clear that I’m not trying to make this either a pro-fat or anti-carbohydrate article or trying to make a low-carbohydrate diet the default choice for anybody. My point is simply that the idea that ‘fat is bad’ and ‘carbs are good’ (or the opposite) is too simplistic to be meaningful.

Not all fat is bad and not all carbs are good. The source, the composition of the rest of the diet, the total amounts you’re eating of each, your activity level and other variables all factor in. Whether you’re talking about health risk or obesity, you can’t simply pin the blame on one factor or the other.

So, under conditions of high caloric intake, with a high intake of refined carbohydrates (meaning chronically high insulin levels), poor quality fat choices (too much saturated fat and/or too little unsaturated fats), little activity, minimal fruit and vegetable intake, etc. a high-fat intake is probably very detrimental from a health standpoint. Sadly, this describes a fairly typical diet in the modern world (especially the US).

In contrast, with reduced or even controlled caloric intake (such that bodyweight goes down or is maintained) and most of the fat coming from unsaturated sources (note: excessive polyunsaturated fats has its own set of problems), a high fruit and vegetable intake, reasonable activity levels, keeping body fat levels down, etc. higher fat intakes may be no problem at all. In some situations, an increased fat intake (again, from healthy sources within the context of activity and a high fruit and vegetable intake) may be beneficial compared to the alternatives (e.g. increasing carbohydrate intake).

In this article, I want to look at carbohydrate and fat intake in terms of the various arguments and debates that tend to surround them.

The main controversy here revolves around what amounts of carbohydrates and/or fat are ideal, healthy, recommended, etc. and that’s what I’ll focus on. I’m not going to deal with body composition explicitly in this article, I’ll save that for another day.

Two (or Three) Dietary Camps

Generally, folks fall into one of two camps regarding whether they think carbohydrates or fats are good or bad. For a couple of decades now, the mainstream of dietary advice has been more or less stuck in the mindset of ‘fat is evil and ‘carbohydrate is good’.

Various attempts to promote so-called ‘high-fat’ or ‘low-carb’ diets have usually been shot down as fads although there is increasing research evidence that, at least for some individuals (usually those with insulin resistance) higher fat intakes and lowered carbohydrates may be both beneficial and preferred.

However, for the most part, I’d say that mainstream dietitians are still on the carbs = good, fat = bad bandwagon with higher fat/lower carbohydrate diets being relegated to the diet ‘fringe’.

Both groups can bring impressive (or at least impressive looking) data to the table but, as usual, extreme stances are invariably incorrect and the truth lies somewhere in the middle; this particularly debate is no different.

The third group (and the one I put myself in) recognizes that whether or not carbohydrates or fats are ‘good’ or ‘bad’ depends on the context. The source of the carb or fat, the rest of the diet, the goal of the individual, genetics, activity, etc. all factor into this issue. So while it may be convenient to give simplistic recommendations of the ‘X is bad, Y is good’ variety, simple in this case tends to be incorrect.

Perhaps the most succinct way of describing what I’m going to detail is that there are no good or bad foods only good or bad diets. That is, within the context of one type of diet or individual situation, a specific food may be excellent; under other conditions it may be a poor choice.

What does the Body Require?

So that some of my comments will make sense, I need to cover a smidgen of nutrient physiology, mainly having to do with the issue of carbohydrate ‘requirements’ (a topic I cover in detail in How Many Carbohydrates Do You Need).

As I think I’ve managed to work into every book I’ve ever written, there is no strict physiological requirement for carbohydrates (this factoid is often used by the low-carb diet groups as part of the rationale for their dietary approach).

Most tissues in the body can readily use fatty acids for fuel just as easily as glucose. There are a few tissues such as the renal medulla, red blood cells and one or two other that can only use glucose. However, those cells essentially make their own glucose by recycling lactate (produced from glucose metabolism) back into glucose.

The brain is in its own weird category. Under most conditions, it relies exclusively on glucose. And while it can’t use fatty acids directly, it can use a fatty acid derived fuel in the form of ketone bodies. After roughly three weeks of adaptation to using ketones, the brain may only need 25 grams/day of glucose or so, which can be made by the body (in the liver and kidney) from sources such as lactate, pyruvate, amino acids and glycerol.

Even the American Dietetic Association bible, the RDA Handbook, states that there is no requirement for dietary carbohydrates. Any decent nutrition or physiology book will state the same. Despite this basic biological fact, many researchers and diet authorities still insist that the majority (50-60% or more) of the human diet should come from carbohydrates.

I’ve seen papers where researchers point out that the body requires no carbohydrates which then go on to say that a proper diet should contain at least 50% carbohydrates. It doesn’t make much sense.

At the same time, outside of a small essential fatty acid requirement (a few grams per day from the fish oils, EPA/DHA), fats aren’t truly required by the body either. All of the tissues I mentioned above will use glucose if you provide it (the heart is an exception, almost exclusively relying on fatty acids for fuel) and the body can make fatty acids out of other sources if need be (this pathway isn’t utilized massively in humans, although a few conditions will make it relevant).

So, outside of the small essential fatty acid requirement, one could make an argument for there being no physiological requirement for fats either.

What does the body then require on a day to day basis if there is no real requirement for either carbohydrates or fats? Well, outside of the basics like water and air, roughly eight amino acids are essential to get from the diet, there’s the small essential fatty acids requirements and of course vitamins and minerals. Everything else, strictly speaking is optional.

I would note that, to avoid starving to death, sufficient calories will be required. Since it’s generally unrealistic to consume your entire daily caloric requirement from protein, that means that carbs, fats, or a combination of the two, will generally be needed to supply sufficient energy to the body.

But, as noted above, most tissues in the body show a great deal of flexibility, using carbs when they are available and fats when carbs aren’t available. Note also that the body has its own store of fuel, primarily in the form of body fat that is mobilized when sufficient amounts of other nutrients aren’t available.

So Why Do Most Argue that Carbs are Good and Fats are Bad?

Despite the fact that there is no physiological requirement for carbohydrates in the human diet, the most common dietary recommendation in modern times is generally to reduce fat intake and increase carbohydrate intake. I’m going to address the issue starting from that standpoint.

A good question might be why is this stance taken. While I can’t read the minds of these folks (and I hate to contribute to grain lobby USDA conspiracy theories), I think the reasons is actually fairly simple: we have to eat something.

There’s usually a limit to how much protein can be reasonably consumed (and most authorities seem to be against ‘high’ protein intakes as well) so that means that the rest of the diet (in terms of energy) must come from either carbohydrate or fat.

In the 70’s, the stigma against dietary fat started to develop and it all pretty much went from there. Fat was implicated as the cause of heart disease, stroke, obesity, you name it and excessive fat intake was blamed.

Since people have to eat something and because of the general stigma against a high fat intake (some of which is warranted, some of which isn’t), policy makers recommend a high-carbohydrate intake by default.

The bigger question is whether or not this is a scientifically defensible position.

I’ll address this issue in more detail in Carbohydrate and Fat Controversies: Part 2