Friday, 27 June 2014

Saturated fats Saturated fats Saturated fats.

George Henderson left the following comment. I think that the information in it deserves a bigger audience.

Saturated fats seem to get the blame for everything nowadays. "Saturated fats clogged my arteries". "Saturated fats gave me cancer". "Saturated fats stole my job". O.K, I've done that joke before.

There are saturated fats, there are saturated fats, there are saturated fats, there are saturated fats, there are saturated fats and there are saturated fats. Saturated fats are an ester of Glycerol (a 3-carbon alcohol) and three saturated fatty acids (SFA's). There are roughly six categories of SFA's.

1) Short chain SFA's such as Acetic acid, Propionic acid, Butyric acid (found in butter and also what soluble fibre ferments into in the colon) and Caproic acid.
2) Medium chain SFA's such as Caprylic acid, Capric acid, Lauric acid and Myristic acid.
3) Long chain SFA's such as Stearic acid.
4) SFA's behaving like Palmitic acid.
5) Odd chain SFA's such as Pentadecylic acid and Margaric acid.
6) Very long chain SFA's such as Behenic acid.

See http://en.wikipedia.org/wiki/List_of_saturated_fatty_acids

In foods, the above SFA's are associated with different things.
1) and 2) don't get associated with much polyunsaturated fatty acids (PUFA's), e.g. dairy and tropical nuts.
3) and 4) are more likely to be associated with long-chain PUFA's, e.g. meats, poultry, temperate nuts.
5) is associated with CLA and not much PUFA's, e.g. dairy from grass-fed animals.

See also Siri-Tarino et al, Forests & Trees and "Eureka!" moments and Chowdhury et al, More forests & more trees and more "Eureka!" moments with cheese.

4 comments:

George said...

There's another variation here; for some reason, perhaps to do with fluidity requirements, an animal can't make a triacylglycerol from 3 SFAs. If necessary, palmitate will be elongated to oleic acid (by DNL) to allow completion of triglycrides. The position of fats in triglycerides alters their effect on serum lipids, mineral absorption, and so on.
For example, "...in a review of the literature on interesterification, (Hayes and Pronczuk 2010) report that a large amount of stearic acid in the sn-2 position had negative effects on the relative HDL-C and LDL-C profile. As stearic acid is generally not found at high frequency in the sn-2 position in natural fats, and is usually considered as hypocholesterolemic (see above), they considered this a concern for manufactured fats. Furthermore, they report that interesterified fats alter the HDL-C and LDL-C ratios and concentrations in the serum of both infants and piglets away from the pattern seen when they are fed their mother’s milk (Hayes and Pronczuk 2010), which generally has SFA at the sn-2 position (Hunter 2001)."
http://www.publish.csiro.au/view/journals/dsp_journal_fulltext.cfm?nid=72&f=AN13536

Different sources of saturated fat (and other fats) also require quite different degrees of heating to be safe or palatable; compare pork chops with pasteurised dairy, for example. It may be that if we looked only at the epidemiology of boiled meat (lower temperatures), such correlations that do exist would disappear or be reversed

Nigel Kinbrum said...

So the Wiki on sat fats "Saturated fat is fat that consists of triglycerides containing only saturated fatty acids." is wrong? I never knew about the middle FA being unsaturated. Sat fats are even more complicated than I thought.

I cook meats from frozen, covered with frozen vegetables, in a glass casserole dish, in a microwave oven. The cooking temperature never exceeds 100°C.

George said...

I think that's wrong, at least for hepatically synthesised TG. Hepatic DNL elongation of palmitate to oleate is upregulated in NAFLD to neutralise NEFA by increasing TGs.
There may be a technical sense in which only fully saturated TGs like MCTs (which are made synthetically) are considered real saturated fats, but the idea that unsaturated and saturated fats are kept on separate TGs in animals strikes me as improbable.

George said...

Here's some info about where fatty acids are found in triglycerides.
http://lipidlibrary.aocs.org/Lipids/tag1/index.htm
It does look as if there are no, or very few, "saturated fats" in animals, according to the wiki definition.