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!
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