Isolated proteins & protein digestion

jsraaf

New Member
Recently read some interesting nutrition comments on another site that discussed, in part, digestion of protein & incomplete or isolated proteins.

Can someone with th required knowledge separate the wheat from the chaff, as it were, in the following comments? What's true & what's not?

Quote:
If you separate the white and yolk of the egg, you get an isolated protein. Any time you separate protein from fat you are left with an incomplete food. The manufacturers of protein powders tell you to mix them with juice or water. Well, let me tell you, folks; you cannot digest protein without fat. When you swallow an egg white, it goes into your stomach and your stomach says, Hey, where is the fat? The white, which is protein, has no vehicle for conversion, so it is converted to sugar.

The same thing happens when you use protein powder. They say to mix with juice or water because they are made of ionized whey protein, which is the skim of cottage cheese. It is not biologically superior to eggs, liver and milk. These powders make you feel good because they are carbohydrated sugar. Sure you are going to put on weight, but it is not going to be muscle weight.

You cannot digest protein without fat, and it must be digested to be converted to amino acids. Once it is digested it goes through the liver and is converted to amino acids. If it is not digested the liver cant do its job.

End quote
 
[b said:
Quote[/b] ]you cannot digest protein without fat.

untrue. protein is digested by proteases while fat is digested by lipases. completely different sets of enzymes.

protein diestion is totally independent from fat digestion. Bear in mind also that protein digestion begins in the stomach whereas fat digestion does not. fat digestion requires bile as an emulsifying agent. that occurs further down the GI tract.

Without going into too much detail, the process of digestion in the stomach is as follows:
presence of food in the stomach (any food) increases levels of a hormone called gastrin (produced by the cells lining the stomach). Gastrin stimulates the release of HCL (acid) into the stomach. The HCL then 'activates' the various proteases allowing protein digestion.
When HCL levels get too high (about pH2), gastrin secretion in stopped.

Fat is not at all essential for this process to occur.
 
Good post Stevie.

The misconception about egg protein stems from biotin and avidin.

Biotin is an essential member of the B complex group of vitamins and is found in egg yolks. Biotin was discovered in nutritional experiments that revealed a factor in many foodstuffs that was capable of curing the scaly dermatitis, hair loss, and neurologic signs induced in rats fed only dried egg whites.

Avidin, a glycoprotein found in egg whites, binds biotin very specifically and tightly. Because it is resistant to pancreatic proteases, dietary avidin binds to dietary biotin (and probably to any biotin from intestinal microbes) and prevents its absorption. (Biotin is also synthesized by the normal bacteria of the large intestine and is partly absorbed in teh lower intestine). Cooking egg whites denatures avidin, rendering it susceptible to digestion and unable to interfere with the intestinal absorption of biotin from the yolk.

This and other dietary facts have caused a great deal of confusion about the dietary relationship between egg whites and egg yolks. The above quote is just an example of how a lack of understanding turns into beliefs that take on a life of thier own.
 
[b said:
Quote[/b] (Bryan Haycock @ April 10 2003,2:12)]Cooking egg whites denatures avidin, rendering it susceptible to digestion and unable to interfere with the intestinal absorption of biotin from the yolk.
What if you don't cook it? I have been using egg substitute as my second breakfast.

Eric
 
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