Anthropology P380:
What are Proteins?
Strings of Amino Acids (polymers) joined by PEPTIDE BONDS
AA's = macromolecules containing NITROGEN
20 Amino Acids= basic building blocks of animal tissue (8-12 AA's are essential to human diet)
Diet must balance AA's in %'s of tissue, or cannot be used to create tissue
Egg= complete essential AA balance = scored at 100
vs Wheat = 37
- Cereals low in amino acids lysine, thrionine
- Legumes rich in lysine & thrionine, but low in methionine
- Maize is low in tryptophan
Cultural Mixes solve the AA balance challenge
(beans & rice, bread & peanut butter)
NOTE: there was a question in class one year about the Amino Acid balance of eggs vs egg substitute products (answer: slightly different, but pretty good mimic). It turns out that all of this data is online at the USDA website. You can get a complete online report of any food you are interested in by searching the USDA Nutrient Database. Try it! It's fast and easy... almost everything you ever wanted to know about the nutritional value of particular food items!
Protein Digestion: in STOMACH
- COSTLY: must break peptide bonds = PEPSIN enzymes
- & each AA has a specific enzyme (e.g. trypsin for tryptophan)
- NH-2 = ammonia = toxic on its own... excrete as urea = water + NH-2
- If you eat too much N -- need LOTS of water... can survive 5-6x requirements, but not much more: (3 lbs steak= toxic dose)
- rest broken into monosaccharides (glucose) & absorbed in small intestine
So, R.D.A. of egg protein for Americans is 0.8g protein/kg body wt / day
70 kg man = 56 g protein/day
MacD Quarter-pounder = 25 g protein... eat 14 of them & you might die! (Just a joke... you would need that much pure protein with no other sources of liquid or energy to reach toxic levels of Nitrogen)
As described in the article by Speth and Spielman, it actually costs more energy to digest protein than is released & absorbed by digesting it: a "specific dynamic action" of +20%.... if your Basal metabolism requires 1600 kcals, you'll need an additional 320 kcal just to digest protein... If you have total energy requirements of 3600 kcal, you would need to eat over 7.5 lbs of lean meat alone to satisfy those energy requirements. If protein is only source of energy (very lean diet)... body can easily go into energy debt...
= starvation mode .. .
- first use up glycogen stored in liver (several hours supply)
- then will start to break down muscle tissue (glucose synthesized in liver)... for 5 days
- then will attack body fat (prolonged starvation)
This can be a problem, as discussed in Speth and Spielman article, if you are living off of wild foods during a lean season -- as in North America during the winter months, when animals lose their supplies of body fat and get very lean. You can starve to death with a full stomach, by eating lean meat.
Read about the "protein sparing effect" = a little carbo or fat goes a long way (and sugars are more efficient to metabolize... especially for big-headed folks like humans).
While our modern domestic animals are bred to be fatty (e.g. marbelized meat...), wild game have very lean muscle tissue to start with, and can lose almost all of their body fat during periods of high activity level and low food intake, such as the rut (note that this differs between male and femal animals). Wild animal fat content can range from 30%-1% of whole body mass... but much of that is tucked in marrow bones and around organs (see marrow figures for African game in Investigating Olduvai CD-ROM). Also, look at the stats for bison meat, below. Bison meat has about a quarter of the fat content of domestic beef, and a slightly smaller proportion of saturated fats.
Historically, native American hunters would pass up a thin bison carcass, rather than eat lean muscle... or just eat the fatty bits. This is also one reason why BONE MARROW is a very popular food among foragers -- a great source of lipids & kcal. We will read, later, about the implications of this type of behavior for interpreting the patterns of meat eating among early human hunters and scavengers.
For example, read about the North American bison
Meat Fat(g) Cholesterol(mg) Calories Bison, Round 2.42 40 143 Beef, Broiled Round 13.1 85 222 Chicken, Roasted 4.1 75 140
Type of fat beef bison Saturated 46.3% 43.4% Polyunsaturated 8.2% 11.7% Monounsaturated 45.5% 45.1% Total Unsaturated 53.7% 56.8% Another interesting issue is the case of grain-fed beef. Wild bovids (Bovidae is the family that includes cows and antelopes) are adapted for grazing on different types of grass, or browsing on the leaves of shrubs, and when they do so the fats in their body reflects the chemistry of those food sources. In particular, their fat has a very low balance of Omega 6/Omega 3 fatty acids. In contrast, the fats of domestic animals fed on grains (e.g. American feed lots are notorious examples) have a much higher n6/n3 ratio. Several authors, such as Loren Cordain and Artemis Simopoulos have argued that a diet high in Omega 6 fatty acids has deletereous health consequences. You can read more detail about this in the LIPIDS lectures.
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Last updated: 10 Sept, 1999
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