What's the straight dope on fats?

At first I thought I knew everything I needed to know: saturated fats are bad, unsaturated fats are good, and trans fats are the absolute worst.

Then I started to learn about omega-3, omega-6, and omega-9, whatever those are. And I think they are good in general. And then, I start hearing that they ARE good, but only if you have a correct ratio, otherwise they are bad!

Then I learn that there are mono-unsaturated and poly-unsaturated fats, both counted as unsaturated, and that they are not equally healthy for you. In fact, evidently, one or both of these are bad.

And then I start hearing about hydrogenated fats, and partially hydrogenated fats, and my mind just reels.

So can please, anyone, give me the straight dope here?

[li]Saturated, Unsaturated, Trans: which are worst/best for you and why?[/li][li]Omega-3, omega-6, omega-9: which are good for you, and why, and are ratios important[/li][li]Hi, Opal![/li][li]Hydrogenated and partially hydrogenated oils: always bad for you or what?[/li][/ul]


if MDs and dietitians can’t get their stories straight on fats, what the hell makes you think anyone here can?

A friend of mine, who is a retired microbiologist, explained something about trans fats to me. I’m going to assume he knows whereof he speaks.

Vegetable fats are (with a few exceptions) UNsaturated. They are liquid at room temperature. Animals make saturated fats, which tend to be solid at room temperature. About a hundred years ago, Proctor & Gamble introduced Crisco, hydrogenated vegetable oil, revolutionizing the culinary experience and quite possibly poisoning a generation or more of American consumers.

Hydrogenation turns unsaturated fat into saturated fat. BUT there’s a nasty fact: Each molecule of saturated fat thus created is randomly cis or trans. Trans fat is sticky. It sticks to itself. It sticks to anything it touches. It sticks to your arteries. It is evil. It does not occur (much) in nature, which leads to a nasty result (discussed below).

Animals make saturated fats too. But by a very different process: Instead of subjecting veg oil to hydrogen under great pressure (the artificial way), animals use enzymes to do their chemistry. This is a MUCH more specialized and selective process, and does NOT create trans fats (other than the occasional stray molecule).

Now, what happens when you get yourself full of trans fat that you’ve eaten: Other kinds of fat, you can metabolize. This is done with enzymes too. But enzyme chemistry is a very specialized and selective process, remember? Your enzymes cannot metabolize trans fat. Since they don’t occur in nature, nobody ever evolved the mechanisms to do it. So the trans fat stays in your system since your body doesn’t know how to do anything with it. And it sticks to, and gums up, everything it touches. So it accumulates in your body over the years. If you quit eating it, I guess your body very gradually can eliminate some of it (e.g., by pissing it away) over time.

The conclusion I drew from hearing about that was, that trans fat is a portion of artificially saturated fat, and is probably the main reason that saturated fat was ever so dangerous in the first place. I conclude that merely saturated (non-trans) fat by itself, as present in animal fat, probably isn’t so bad. It’s the trans that kills.

ETA: You can easily google up many articles discussing this. Without having read them myself, I won’t stick my neck out and post any links here. But there’s information out there.

Trans fat is undoubtedly the worst kind of fat by far - if it is artificial trans fat, since trans fat also naturally occurs (in a different form, conjugated linoleic acid, which has both a trans and cis (the normal isomer) configuration) in beef and dairy, but the natural form doesn’t appear to be harmful and may even be beneficial (the findings on high-fat dairy consumption, relative to low-fat, here may reflect this, despite dairy also having saturated fat, which appears to just cancel out the effects of CLA alone).

Saturated fat is considered to be bad because it raises cholesterol levels; however, unlike trans fat, it increases HDL as well as LDL (however, not all saturated fat is the same; stearic acid for example doesn’t raise LDL, unlike palmitic acid). In fact, saturated fat raises HDL by the most of any fat, according to the first article cited here.

As for omega-3 and omega-6, I have also heard that it is the ratio that is more important and the average American eat far too much omega-6, something like 2-5 times the optimum ratio; Wikipedia makes omega-6s sound like the real bad guy behind heart disease, obesity, cancer, etc, describing them as “prothrombotic, proinflammatory and proconstrictive”.

Also, one thing to note is that hydrogenation doesn’t necessarily produce trans fat, since if the oil is fully hydrogenated (some products explicitly note this, although you should assume otherwise if they don’t say) the result is saturated fat (trans fat can only be unsaturated), while while not good in high amounts, is much less harmful than trans fat, although I don’t know if the saturated fat produced is the same as the saturated fat in, say, meat.

Saturated fat is also needed for testosterone production.

See what happens when you get your ignorance fought by a message board? :rolleyes:

This is exactly contradictory to what I think I know (see post #3 above), which is that trans fat can only be saturated, being a particular configuration of saturated fat molecule that is produced by the artificial hydrogenation process.

What I think I know is (post #3) is that each molecule of saturated fat produced by hydrogenation will randomly be cis or trans, implying that hydrogenated vegetable oils would be about 50% trans fat. I’ve never actually seen that stated explicitly, though. And now that the dangers of trans fat are known, the folks who make hydrogenated oils have developed ways to produce it without the trans fat, so your Crisco is much safer now.

Thanks for the info so far guys. Anybody else got anything to add, especially in relation to polyunsaturated vs monounsaturated fats? And what the heck does hydrogenation do? Does it turn unsaturated into saturated? or mono into poly? Or unsaturated into trans? <_< And what’s the difference between partially hydrogenated and just plain’ ol hydrogenated.

I think he’s right. See http://en.wikipedia.org/wiki/Cis–trans_isomerism

Hydrogenation reduces unsaturation. It makes fats monounsaturated, then saturated. They do it to turn oils solid and make them resist spoilage.

“Here, let me google that for you” . . .

See, you’ve got me showing off (in my posts above) that I probably know just enough to be dangerous. But this got me interested enough to do a bit more reading on it. Here’s a starter: Wiki article on Hydrogenation, with a section on industrial applications, including hydrogenation of fats in the food industry.

Fats, like many other Carbon/Hydrogen/Oxygen (CHO) compounds, have long chains of carbon atoms, with other atoms hanging off of them.

Carbon atoms have four bonds, meaning they can connect up with four other atoms, one bond to each. Thus, a typical carbon chain has a row of carbons connected by single bonds, often drawn as
leaving two other bonds on each C to hang other atoms (often H) off of them.
But two adjacent C’s can have a double bond between them, often drawn as
so each of those C’s has only one leftover bond to hang an H from.

And you can have two double bonds in a row, like this:
so that C in the middle has all its bonds occupied, with no room for any H to hang from it.

An UNsaturated fat has some of those double bonds, meaning that it does NOT have a full complement of H’s. A POLYunsaturated fat has several such places in it. This is healthy.

A SATURATED fat has all such double bonds reduced to single bonds, with the extra bonds thus opened up for hanging H’s off of them, and with those extra H’s there. This is UNhealthy.

A MONOunsaturated fat has ONE such double bond where H’s are absent. From the wiki on Monounsaturated fat:

Wikipedia has an article on trans fats that says the following:

Trans fat is the common name for unsaturated fat with trans-isomer (E-isomer) fatty acid(s). Because the term refers to the configuration of a double carbon-carbon bond, trans fats are sometimes monounsaturated or polyunsaturated, but never saturated.

So Trans-fats are a type of unsaturated fat… either mono or polyunsaturated, but never saturated.

So the takeaway so far from what I’ve learned here is…

You should avoid too much saturated fat as it has bad effects on your cholesterol counts, which can cause heart disease.

Unsaturated fats are typically good for you (or at least, don’t have correlation with heart diseases and such).

Omega-3, 6 and 9 have been correlated with good heart health, as long as they are in the proper ratio (what is the ratio, and what do you eat to get it?)

Transfats are a special type of unsaturated fat that are particularly bad for you.

Hydrogenation is a process that turns unsaturated fats into saturated fats or monounsaturated fats (is that the difference between partial and fully hydrogenated?), so it’s bad for you only so far as that it is turning otherwise benign or healthy fats (unsaturated) into fats that raise cholesterol (saturated).

Is that about right?

Hey, we’re ninja’ing each other, and from the some of same sources even!


ETA: Okay, I see the point about trans fat never being saturated. I was focusing on the wiki’s on hydrogenation and mono-unsaturated fats, which emphasize the differences between those two forms.

Haha indeed. Thank you for the chemistry lesson. I appreciate it!

Now… what about monounsaturated vs polyunsaturated as far as health concerns go? It sounds like polyunsaturated fats are the absolute best for you, but are monounsaturated fats unhealthy, or just not quite as good? If we had to rank all fats, would be something like

BEST FOR YOUR HEALTH ----> Polyunsaturated ----> Monounsaturated ----> Saturated ----> Transfat —> WORST FOR YOUR HEALTH

And, another thing… just to get more complicated, is a hydrogenated fat inherently worse than a naturally occurring fat of the same type? So now it might look something like this…

BEST FOR YOUR HEALTH ----> Polyunsaturated ----> Transfat (Natural) ----> Monounsaturated (natural) ----> Monounsaturated (hydrogenated) ----> Saturated (natural) ----> Saturated (hydrogenated) —> Transfat (Hydrogenated) ----> WORST FOR YOUR HEALTH
And, where exactly do the omega 3, 6 and 9 come in? They are just fatty acids… not fats themselves? Do you have to just take supplements to get them, or are there basic foods to obtain the right “ratio” of 3:6:9?

That same paragraph you included from that wiki has an additional two sentences that seem relevant:

Actually, this is the first I’ve ever read that ANY kind of trans fat could be good for you. How confusing is THAT? Curiouser and curiouser.

Yes I did read that and I was blown away. I think this would actually make a really good Straight Dope article, if Cecil or one of the SDSAB members felt like taking it on. It’s just all so confusing.

And what the hell is the difference, molecularly, of a transfat (or monounsaturated or saturated fat) produced by enzymes, and one produced by hydrogenation?


Artificial trans fats have a linear structure; all of the carbon atoms are in a straight line while cis fats are bent at the double bond(see examples here), while natural trans fats also have a cis- configuration in addition to a trans- configuration. For example, rumenic acid (the main trans fat in beef and milk), which has two double bonds and is bent at both of them in folded-over structure (note however that vaccenic acid, which is also found in human milk, is similar to artificial trans fat, but is converted during digestion to rumenic acid; these are also both omega-7 fatty acids, as opposed to omega-3/6/9).

Also, with this in mind, there is a push to differentiate between natural and artificial trans fats on food labels (for example, many beef products will show trans fat, although dairy generally doesn’t have enough to meet the 0.5 gram minimum; IMHO this should also be changed to show milligrams like cholesterol, since there are a lot of foods that claim to be trans fat-free but have partially hydrogenated oil in them).

It may have something to do with the molecular shape; saturated fat is similar to trans-only fat in that both are linear molecules. Note however that there are also different kinds of saturated fat; for example, stearic acid doesn’t raise LDL like palmitic acid (which is why palm oil is bad for you). Also, as mentioned in previous comments, saturated fat does have some positive health effects, so in moderation it is much better than trans fat; for example, it raises HDL, which helps counteract the effect of some saturated fat raising LDL as well, while artificial trans fat lowers HDL and raises LDL, the worst possible outcome (the HDL-LDL ratio is more important than the absolute level, within limits).

Also, something that I have wondered about, but haven’t found anything on, is whether saturated fat has more calories (if even a little) than unsaturated fat, since the former has more hydrogen in it, thus more oxygen is needed to oxidize it; for example, if there were two more hydrogen atoms in a saturated fat vs. unsaturated fat (otherwise the same number of carbon atoms), those extra hydrogen could form an extra water molecule, with an enthalpy of formation -285.8 kJ/mol (liquid water) greater than the unsaturated fat.

Here’s an interesting article that finds that carbohydrates, when replacing saturated fat, are associated with higher blood pressure, LDL:HDL, and triglycerides, at least in people who already have high LDL/triglycerides:

You said it better than I could have. Just in the past 20 years several pieces of nutritional advice have had to be revised. E.g. The body makes cholesterol if you don’t eat any. It is essential. Twenty years ago, cholesterol was considered just this side of poison. Twenty years, it was considered that the thinner you were (short of actual anorexia) the better. Now it seems that people my age are better off–live longer–with a BMI just above 25 than in the range 20-25. In five years, I make a prediction here, they will discover that they have confused cause and effect, post hoc, ergo propter hoc. Marian Nestle claims over and over (including in Scientific American) that all calories are equivalent and others dispute this. What is the truth? Damfino. But maybe in ten years there will be an answer. Meantime, eat sensibly. And eat butter, not margarine. Why? Well we evolved eating animal fat, not hydrogenated vegetable oil. It also tastes much better. Just don’t eat too much of it. Maybe.

The problem is there is no Straight Dope on this except given by those whose are sure of more than what they have rights to be sure of. It is without question confusing right now.

Just take a look at the article linked above … the quote was just from the introduction. What the study found was more interesting: the response to saturated fat depends on how much carb intake. Which of course implies something about what else is being eaten and not eaten.

Here’s another recent article that tries to tease out what does what, a large meta-analysis.

And here’s another recent review.

And a response to it.

What we can say is that the typical Western diet, high in processed trans-fats and simple carbs, relatively low in fiber from both whole grains and from real vegetables and fruits, is associated with worse outcomes than many other alternatives, some that vary in apparent opposite directions. Beyond that gets difficult to parse out.