Page 97 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 97

Box 5-8. Cis and Trans Fatty Acids. Box 5-9. Long-Chain vs. Medium-Chain
VetBooks.ir When carbons are connected by a double bond, rotation around Fatty Acid Metabolism.

the bond is not possible resulting in fatty acids that are either
Medium-chain fatty acids (mcFFA eight to 12 carbon lengths)
cis (with the carbons being on the same side) or trans (with the are a minor component of natural compounds such as triglyc-
carbons being on the opposite side). Most polyunsaturated fatty erides from mother’s milk or coconut milk. Triglycerides con-
acids are in the cis configuration. Fatty acids can be converted, taining mcFFA are assigned the name medium-chain triglyc-
however, to the trans configuration during excessive heating or erides (MCT). Even in foods “rich” with MCT, the overall contri-
through partial hydrogenation (i.e., the production of margarine bution to the fat component of those foods is minor, compared
from oil). Although trans fatty acids are metabolized for energy with long-chain triglycerides. However, because MCT are sub-
and incorporated into storage lipid, similar to the cis isomers, ject to different metabolic regulation they may prove useful in
they are not further metabolized to eicosanoids. Nutritionally, certain disease states and have been included in some foods
trans isomers are in many ways like saturated fatty acids in that formulated for specific diseases (Table 1).
they are used for energy but cannot function as essential fatty
acids. The Bibliography for Box 5-9 can be found can be found at
www.markmorris.org.

Table 1. Comparison between medium-chain triglycerides
temperature and fatty acid composition. A more unsaturated (MCT) and triglycerides.
(increased number of double bonds) fatty acid makeup results
Process MCT Triglycerides
in fats that have lower melting points compared with those of
Gut hydrolysis Rapid, 5x triglycerides Slower rate than
fats made from more saturated (decreased number or no dou- MCT
ble bonds) fatty acids. The length of the carbon chains in the
Absorption 2x faster than Slower rate than
fatty acids making up a fat also changes the melting point. Fats
triglycerides MCT
that contain fatty acids of shorter carbon chain length have
lower melting points than do fats that contain longer fatty Enterocyte Free fatty acid Free fatty acid
reprocessing not reassembled reassembled in
acids. Animals take advantage of these differences in physical
in triglycerides triglycerides
characteristics to synthesize phospholipids containing appro-
Transport Portal vein, Chylomicrons,
priate classes of fatty acids that allow for membrane fluidity at albumin bound lymphatics and then
physiologic temperatures. general circulation
Hepatocyte
Omega-3, Omega-6 and Omega-9 Esterification Not esterified to CoA Esterified to CoA
Fatty Acid Families
Carnitine Not bound to carnitine Bound to carnitine
Fatty acids with the first double bond between the third and
fourth carbon are in the omega-3 family, sixth and seventh car- β-oxidation Unregulated Regulated
bon the omega-6 family and ninth and tenth carbon the

Table 5-18. Classification, structure and function of general lipids.

Classification Structure Function
Hydrocarbons -CH , -CH , -CH Building blocks
2
3
Nonesterified fatty acids CH (CH )n(CH )nCOOH
3
1
2
Saturated Stearic, palmitic Energy, membrane fluidity
Monounsaturated Oleic, palmitoleic Energy, membrane fluidity
Polyunsaturated Omega-3, omega-6 Precursors of eicosanoids and prostaglandins
Simple lipids Fatty acid + alcohol in ester bond Energy storage, insulation
Triglycerides Glycerol + three fatty acids
Complex lipids
Phospholipids Diacyl glycerol 3’ phosphate Membrane lipids
Lecithin 3’ phosphocholine Emulsifying agent
Cephalin 3’ phosphoserine/ethanolamine CNS membrane
Inositol Carbohydrate (3’ phosphoinositol) 2nd messenger
Ceramide Sphingosine + fatty acid CNS membrane
Sphingomyelin Ceramide + phosphocholine Myelin
Glycolipids Sphingomyelin + carbohydrate CNS membrane/recognition
Cerebroside Ceramide + monosaccharide
Ganglioside Ceramide + oligosaccharide
Prostaglandins 20-carbon polyunsaturated fatty acids Paracrine and autocrine action
Sterols and steroids Four-ring hydrocarbon structures Bile acids, hormones, membranes, lipoproteins,
cholesterol, cholesterol esters
Fat-soluble vitamins See vitamins See vitamins