Posted: February 9, 2011 in biochemistry, chemistry

Fat is all the rage: From dissing trans to flaunting omega-3s, everyone who is anyone is talking about it. But what has made fat so phat?

Lipids are composed of hydrocarbons and are insoluble (or have limited solubility) in water. This category of organic molecule includes a relatively diverse range of compounds, including waxes, terpenes, steroids, oils, and, yes, those things we call fats. In addition, “fat-soluble” vitamins (A, D, E, and K) are themselves lipids. This is why you are told to add fat to your salad – since they won’t dissolve in water you don’t get these nutrients unless you emulsify them!

A primary role for lipids is maintaining a barrier between the hydrophilic and homeostatic internal cell environment and dynamic external conditions. Phospholipids play the role of protective barrier, forming that selectively, semi-permeable plasma membrane around our cells. Cholesterol is a lipid steroid that is a CRUCIAL cell membrane component, buffering us against temperature and providing other unique functions. We’ll talk more about that later.

In addition to being major cell membrane components, lipids are essential for cellular signaling (e.g. hormones), immune function, and serve as our long-term energy storage molecules (you already know this, though probably in less-politically-correct terminology…). Fat is more efficient than other macromolecules at storing potential energy (as trapped in the chemical bonds), holding 9 kcal of chemical potential energy per gram.

Fats and oils are composed of the three-carbon alcohol glycerol attached to one, two, or three fatty acid chains. When all three of the glycerol carbons are condensed with a fatty acid “tail,” we know the resulting molecule as a triglyceride.

Hydrocarbon chains can be saturated or unsaturated. Saturation just means that all the carbon atoms have four (their maximum!) single bonds, while the degree of unsaturation corresponds to the number of double bonds introduced between carbon atoms. Since the general definition of “saturation” implies being filled or full, it makes sense to conceptualize that the chemical bonding capacity is fully utilized in saturated compounds.

Notice how the double bonds produce “kinks” in the chain? As it turns out, the level of unsaturation corresponds to the fluidity of the fat. That’s why saturated fats are solid at room temperature, while polyunsaturated fats tend to be fluid. “Trans” fats are artificially (usually) produced double bonds (“hydrogenation” is the chemical process of introducing trans-double bonds to a fatty acid chain – watch out for this sneaky label terminology); however, they fail to produce the characteristic kinks in fatty acid chains. The maintenance of a rigid (straight) structure allows for a more solid form and gives us margarine and shortening. However, your body isn’t fooled by this fake stuff and we now know it was a really, really bad idea…

What else is a bad idea? Taking anabolic steroids. Well, okay, that is purely opinion and doesn’t always hold true but you see my point. Which is to transition into talk about the steroid class of lipids. All steroid compounds have a characteristic carbon backbone of a fused, four-ring structure on which various functional groups are attached.

Cholesterol, a good guy, is synthesized by our bodies (no dietary input needed!) and, in addition to serving as a crucial membrane component, also serves as a precursor to sex hormones and Vitamin D (a conversion pathway activated by unfiltered sunlight!). The way your body transports insoluble things like cholesterol from cell to cell, through your bloodstream for instance, is by packing them up inside spherical carrier molecules…

Lipoproteins are globs of protein and lipids all intertwined. These are categorized according to density. Since fat is less dense than protein (think: fat floats, meat sinks), lower density lipoproteins are those that have a relatively high proportion of fat to protein. On the other hand, higher density lipoproteins have a higher ratio of protein to fat. But wait a second! Do those terms sound vaguely familiar? I hope so! Low-density lipoprotein and high-density lipoprotein are also know as LDL and HDL, respectively. Cholesterol is cholesterol; but to be healthy we need protein-packed HDL delivering it to all the right places. LDL is not so efficient at distribution, and also tends to accumulate in the body’s passageways.

Okay now to the really hot topic. The term omega, as it relates to fatty acids, refers to the terminal carbon atom farthest from the functional acidic (carboxyl) group. In other words, polyunsaturated fatty acids have two distinctive “sides,” or endings. On one side is an acidic carboxyl group (let’s call this the “alpha” end), while on the other side lies an “omega” end. The number associated with a type of fat defines the position of the first double bond (unsaturation) relative to the omega end. For example, omega-6 fatty acids have a double bond on the sixth carbon atom from the omega side.

There are three major classes of omega fats that are important in our diet. These are omega-3s, omega-6s, and omega-9s. All three serve functional physiological roles, and it seems fairly meaningless to discuss the requirements for each individually. What seems relevant and important to our health is the RATIO of each in our bodies. It appears optimal to have relatively high levels of omega-3s, medium levels of omega-6s, and low levels of omega-9s. However, the American diet has become heavy in omega-9s (largely from animal and processed sources), overly high in omega-6s (found in many plant-based oils, as for fried foods), and dangerously sparse in omega-3s (you know, seafood and such). Clinical studies suggest that altering our ratio of intake, rather than focusing on an individual fat type, is the most effective way to create positive biochemical changes in our bodies.

A review of recent research discloses mounting evidence that disturbances in fatty acid metabolism may link chronic psychological stress, endocrine responsiveness, and psychopathology. In particular, relatively lower omega-3 status corresponds to negative outcomes in physiological stress response. Research also suggests that the compositional changes made by our bodies to specific fatty acids may be able to serve as markers for stress and indicators for disease in the future (Laugero et al. 2011).

Click here and click here for fantastic sites to use while studying lipids!

  1. Karolyn Hernandez says:

    So when doctors say “your cholesterol level is too high” are they talking about LDL and HDL?

  2. That’s right! LDL is known as “bad” cholesterol. HDL is known as “good” cholesterol. These two types of lipids, along with triglycerides and Lp(a), make up your total “cholesterol” count.

    A count above 150 (measured in mg/dL) is considered risky – but again with the ratios: You NEED at least 40 mg/dL of HDL to be healthy, and most doctors would suggest you aim for an HDL count well over 60. This implicitly limits the LDL level. Changing the ratio to favor HDL over LDL is often the first step in combating disease.

    Having an HDL level below 50 or so puts one at significantly elevated risk for heart disease! My personal physician is adamant that I maintain HDL levels above 75. On the other hand, the optimal LDL level is roughly 25! However, it seems safe to have LDL up to 100 mg/dL – as long as HDL levels are appropriately high to maintain a positive ratio.

  3. Jeanette Hernandez says:

    Is cooking oil considered unsaturated prior to cooking since it’s a liquid at room temperature? And since cooking oil gets hard as it then cools down, does that make it unsaturated?

    • I’m not sure what type of oil you’re referring to? Many commercial cooking oils are actually mixes of more than one type of fat; some of these may be saturated and some unsaturated. Will you clarify what you mean when you say “hard as it then cools down”?

  4. Jeanette Hernandez says:

    I occasionally use vegatable for cooking or frying up certain foods. I usually wash the pan after the vegtable oil cools down. But by that time, it has cooled into a hard substance, for lack of better word. Frankly, it kind off gross me out. Does that make sense? I heard someone once say that cooking oil, once it’s been used and is left out it is then unsaturated and that it was bad for you. I wondered if there was any truth to that. Thanks!

    • Hmmm… I honestly don’t know why vegetable oil would solidify after you used it!! But it kinda grosses me out, too 🙂

      As a general rule, unsaturated fats are “better” for you, which generally means fats that are more fluid, but this statement must usually also be qualified.

      What are you frying? Maybe some meats/etc. that contain saturated fats themselves are contributing to this phenomenon? Otherwise…. I don’t know!!

  5. Jeanette Hernandez says:

    In addition to my previous response:
    What I meant by “hard as it then cools down” is that once it’s cold it becomes a solid vs a liquid.

    • Kaleigh Polak says:

      So is it bad for us to take omega 3-6-9 vitamins? should we only take omega 3?

      • Well, first of all, when you read Fitness or Health or WebMD or any other source, the statements and advice are directed toward an AVERAGE of ALL people. That means that any given person will not individually be able to follow those rules strictly. While guidelines are good, each of our bodies is unique, and in addition we have changing circumstances. But in general, you should take whatever supplements 3-6-9 or a combination thereof, that works for you, and is tailored to your individual needs as determined by you and your healthcare providers. Remember that you need the appropriate RATIO of each fatty acid, rather than focusing on a particular one.

        The other issue is that there are MANY DIFFERENT fatty acids in the omega-3, omega-6, and omega-9 CATEGORIES. These are merely GROUPS of similar substances, rather than actual things. So that means that you may need a SPECIFIC omega-3, but not others. This, again, is highly individualized. In general, though, no matter who you are, there are some fats that seem to be all-around “better” than others in supplement form. ALA, EPA, and DHA are three omega-3 fats that we cannot synthesize (create from scratch) in our bodies and are nutritionally important.

        The total recommended intake of omega-3s per day is about 1.5 grams. But not only does it matter what form the fat is, it also matters where it came from. The source of your supplemental (or natural) fats matters as well, just to confuse things a bit further.

        Bottom line: There is no “bad for us” or “good for us” – there is only a “what works for me right now.” Incidentally, what works for me (right now) is to take the Vitafusion Gummy Pre-Natal vitamins. Compared to other supplements, these are higher in B-vitamins, obscure trace minerals, and contain each of those important three omega-3 fatty acids. Since they are gummies, they are already dissolved in semi-solid form and are therefore easy for my body to process (“absorb” and distribute). Not to mention they taste like candy. And I love candy.

  6. I’ve never observed this phenomenon – Maybe one of our colleagues has an idea? The closest I can come is maybe that many saturated fats are solid at room temperature but melt as they get hotter (e.g. butter in a skillet)?

  7. Ken Cochran says:

    Regarding the hard fat, liquid fat question:

    Liquid fats are generally fats which are expressed from oil bearing seeds such as soy, cotton seed, safflower, etc. Olives are also a source of liquid fat although the fatty acid distribution in olive oil differs from that of soy, sunflower, etc. Seed fats tend to be poly-unsaturated; that is they contain more than one unsaturated carbon-carbon linkage in the lipid chain. Olive oil contains primarily mono-unsaturated carbon chains. Solid fats are generally of animal origin such as that from beef, pork, etc. We know these fats as lard, bacon fat, pork belly, etc. Another form of hard fat is that obtained by partially hydrogenating liquid fats. Think Crisco. This process is the source of the dreaded trans fat. The process of chemically hydrogenating an unsaturated fat actually changes some of the cis-isomer configurations to trans-isomer configurations. The body does not have an effective way to process the trans-isomers. The result that the breakdown of fats containing these isomers produces free radical polymerization reactions which, in and of themselves, cause cellular damage. As importantly, studies show that the metabolism of the trans-isomer lowers the level and “good cholesterol” and raises the level of the “bad”.

  8. Ken Cochran says:

    One more side note:

    Butter is not pure fat. It is a water in oil emulsion. Generally, butter contains about 80% butter fat and 15% or so of water. Saturated fat in butter comprises about 60 % of the total fat. The remainder is primarily mono-unsaturated fat. Like all animal fats, butter does contain a significant amount of cholesterol.

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