Posted by Larry Hoover on April 5, 2003, at 11:25:39
In reply to Re: Another fish oil question! » Larry Hoover, posted by Viridis on April 4, 2003, at 23:07:46
> Hi Larry,
>
> That's a very helpful link, but in the version that I pull up, there doesn't seem to be a "20:5" (= EPA) column. So, is EPA in there under another heading?I know you've found the answer to this one. I don't know why the different fatty acids are organized the way they are, but you'll find them (EPA and DHA) on different pages.
Incidentally, if you shorten the URL to the word food, you'll get to an index page that sorts foods by a huge variety of nutrients. Play with it.
http://www.cs.princeton.edu/~ah/food/
> Also, just to clarify -- I'm not a chemist, although I am a biologist: I assume that the first value refers to the number of carbons in each chain, and the second describes the degree of "unsaturation" (i.e., number of C=C double bonds).
Exactly right. However, as a short-hand, it has a peculiar weakness. It doesn't tell you where the double bonds lie. For example, gamma-linoleic and alpha-linoleic are both 18:3, but one is omega-3 and the other omega-6.
> I could look this up, but am hoping that besides verifying (or correcting) this, you might elaborate a bit on the nutritional value of long vs. short-chain fatty acids and level of hydrogen saturation.
>
> Thanks!
>
> ViridisA bit? This is a huge topic.
Some gross generalizations:
1. Saturated fats are heart-neutral. They are sources of energy. Short-chained sats, as found in e.g. coconut oil, may have health-promoting effects. (The general shunning of sat fats is not supported by the evidence.) The worst thing McDonald's ever did was turn away from beef tallow for frying french (freedom??) fries.
2. Trans-fats are bad. Much of the negative publicity given to sat fats really belongs to trans fats. Trans fats are man-made, arising from incomplete saturation of the polyunsaturates found in vegetable oils. If a product has "hydrogenated", or worse, "partially hydrogentated", as part of its ingredient list, steer clear. These modifications are solely to improve the profitability of the food processor, by extending shelf-life of the product (among other things).
3. Mono-unsaturates are good. Olive oil, the dominant dietary source of monounsaturates, is good.
4. Polyunsaturates are good, with one qualifier. Most people get too much omega-6, and not enough omega-3. Don't be surprised if you come across a new medical disorder "omega-3 deficiency syndrome", sometime in the near future.
What makes polyunsaturates special? Each unsaturated position is a reactive site. That means the body's enzymes can modify the chemical structure of the polyunsaturates once, twice, many times over. These modifications turn them into signalling/regulatory compounds. We're just starting to understand how this all works, but if you plug eicosanoid or prostaglandin into your search engine, be prepared to be overwhelmed with information.
Another thing that makes polyunsaturates special is the effect each double bond has on fluidity. Saturated fats are solid, even at physiological temperatures. Polyunsaturates are key components of cell membranes, and their fluid nature ensures proper functioning of receptors. Moreover, when a receptor is activated, it can take a part of the cell membrane adjacent to it, and modify and release some of those polyunsaturates as signalling compounds (termed second-messengers).
Bottom line? I think low-fat dieting is a horrid mistake.
I'm having trouble restricting my reply. Perhaps specific questions are appropriate now?
Lar
poster:Larry Hoover
thread:216119
URL: http://www.dr-bob.org/babble/20030402/msgs/216440.html