Anthropology P380: Lecture 6: Fat and protein
Lipids = dietary fats, oils, waxes and sterols (e.g. cholesterol)
~9kcal/g = energy rich because of structure
LIPIDS are an excellent source of concentrated energy: ~9kcal/gram of fat.Like sugars, they contain carbon, hydrogen and oxygen, but structured differently -- structure determines caloric value, and ounce for ounce (gram per gram) the structure of lipids is energy-rich .
Speth and Spielman summarize how foragers can try to offset the dietary deficiencies of high protein diets by focusing on fat rich foods:
selective hunting for species with high body fat processing to extract fat from bones or tissues gathering of oil-rich plant foods (e.g. nuts) gorging on fat when it is available
Lipids are composed of a backbone molecule called GLYCEROL to which are attached 2 or 3 long chains of carbon called FATTY ACIDS.
Lipid: Glycerol + 2 or 3 Fatty Acids
- Di-glycerides are mostly plant oils & waxes
- Tri-glycerides are mostly animal fats
Fatty Acids = Carbon Chains
Palmitic Acid: 16 carbons
(principle FA in milk)
Length of FA Chains:
- fewer bonds = melt at lower temperature
- more digestible
Saturation: ratio of Hydrogen / Carbon
- fewer bonds = melt at lower temperature
- more digestible
(most H )
(more double bonds)
short chain FAs
BUTTER = saturated, but short-chain FA's
melt at lowest temperatures
faster to digest
longer chain FAs
solid at higher temperatures
slower to digest
LARD = 60% saturated F.A.'s
"Hydrogenated vegetable oils"
CORN OIL = poly-unsaturated FA's (liquid)
Chemical & Physical properties of FAT determined by kinds/ %'s of Fatty Acids
Saturation of fatty acids depends on ratio of hydrogens to carbons on chain... the more saturated the fat, the higher the melting temperature. These fatty acid attributes distinguish the melting point, digestibility, & nutritional properties of the lipids -- the chemical and physical properties
Fats digested in large intestine:
- NOT water soluble, must be emulsified
- bile acids break down = "salts" or detergents
- (e.g. lauryl sulfate in shampoo)
- slowly absorbed by mucosal cells
- long/saturate fatty acid chains poorly absorbed
- physiological feedback slows stomach to maximize absorption
- FA's and glyceride molecules coated with envelopes of phospholipid-protein, to form complexes that transport lipids through lymph and blood system to liver or adipose tissue
- HDL = high density lipoprotein
- LDL = low density lipoproteins
Specific nutritional need for lipids? A few:
- important vehicle for fat-soluble vitamins
- cholesterol forms nucleus of Vit D molecule, regulatory & sex hormones, etc, and is synthesized in liver and intestine
- 3 essential fatty acids: linoleic, linolenic, arachidonic which canot be synthesized metabolically, important for cell membrane growth, skin, etc
Can generally meet all specific nutrient needs with just 15-10 g fat/day (ca 1Tb vegetable oil).
Note that the USDA Nutrient Database includes details of the Fatty Acid composition of many foods. So, if you want to really know details of what you're eating, you can!
An interesting issue: ratio of Omega 6/ Omega 3 fatty acids in diet:
n6 / n3 ratio
10-15 / 1
2 - 4 / 1
cereal grains (grass seeds)
21.6 / 1
0.09 - 0.12 / 1
a theory by Loren Cordain, Colorado State (reported to Paleodiet Discussion Group)
Date: Wed, 17 Dec 1997 17:17:00 -0700
From: Loren Cordain
Re: n6/n3 ratio
"I would like to respond to Robert's question regarding the ratio of omega 6 fatty acids to omega 3 fatty acids in grasses. Grasses are members of the gramineae plant family of which cereal grains are a prominent member. Grasses are composed of both leaves and seeds, and the seeds (grains) of commonly consumed grasses (wheat, rye, barley, oats, maize, millet, sorghum) form the staple food of virtually all of the people on earth."
"Polyunsaturated fats are classified by the length of the fatty acid carbon chain, by the number of double bonds and by the location of the last double bond from the omega end of the fatty acid carbon chain. Linoleic acid (a common fatty acid found in salad oils) is labeled 18:2n6 (that is, there are 18 carbon atoms forming the fatty acid chain; there are 2 double bonds; and the terminal double bond is located 6 carbon atoms from the omega end of the fatty acid chain). Alpha linolenic acid is a common omega 3 (n3) fattty acid and is labeled 18:3n3 (there are 18 carbon atoms forming the fatty acid chain; there are 3 double bonds and the last double bond is located 3 carbon atoms from the omega end of the fatty acid chain). There are other polyunsaturated fats of both the n6 and n3 families with carbon lengths greater than 18 (20, 22 primarily) which are mainly found in animal food sources. The 18 carbon fatty acids of both n6 and n3 families are primarily, but not exclusively found in foods of plant origin. The ratio of dietary n6/n3 fatty acids has important human health implications including the development of coronary heart disease, cancer and autoimmune diseases. The estimated n6/n3 ratio in modern western diets is about 10-15:1, whereas in pre-agricultural diets, it has been estimated to be from 2:1 to about 4:1. The high n6/n3 ratio in western diets stems from the excessive consumption of vegetable oil based fats (margarines, salad oils, etc) which have been incorporated into the food supply since about 1913 and particularly after WWII."
"In my soon to be published manuscript on the deleterious effects of cereal grains upon human health, we report the average n6/n3 ratio of the 8 most commonly consumed cereal grains to be 21.6. Thus, the seeds of grasses are quite high in n6 fats, and extremely low in n3 fats. The exact opposite situation is to be found in the leaves. Salem (1) has shown the n6/n3 ratio to range from 0.09 to 0.12 in the leaves of two grass species. Because the leaves of grasses form a much greater bulk of the entire plant, it would be expected that for a foraging herbivore consuming the entire grass plant (grains and leaves), the dietary n6/n3 ratio would quite likely be less than 1. Since the type of lipid an animal consumes is directly reflected in the type of lipids in both storage and structural fat, then free ranging animals consuming grasses will have lower n6/n3 ratios in their tissues compared to feedlot animals consuming only the grains of grasses. Humans consuming the tissues of free ranging animals will also have lower n6/n3 ratios in their own tissues than compared to individuals consuming feedlot animals which have been "finished" upon cereal grains. The consumption of free ranging animals is a very old human practice - the consumption of feedlot fed animals is a relatively new practice, and with obvious health ramifications."
1. Salem N. Omega-3 fatty acids: molecular and biochemical
aspects. In: New Protective Roles for Selected Nutrients. GA Spiller, J Scala (Eds). Alan R. Liss, New York, 1989, p. 127.
Other, more detailed, online references to dietary fats and oils include:
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