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Soy vs. Whey
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Q. Which protein powder is better - Soy or whey? What's the difference?

Disclaimer:
This won't attempt to resolve questions of 'is soy good or harmful' for you (largely because I don't believe there IS a clear answer out there to that question yet. )

HOWEVER, I targeted the primary reasons a BFL person is looking at protein powders - pure ingestion capacity of soy vs. whey protein with the idea that the real question most people on this board are asking is "which one (soy or whey) will give me the most bang for my ingested buck?".

I do touch on other factors, but be aware that this is a HUGE area of study, and so like any thing where you're changing your lifestyle drastically, please check with a doctor for any potential impacts to your known health situations.

Protein Powder (General Info):
The four types of protein used in protein powders are whey, soy, egg and rice. Protein powders can contain one of these, or a mixture of two, such as soy and whey or whey and egg. Other sources rich in protein (other than powders) include meats, soy products, vegetable protein, and dairy protein.

Egg Protein:
Egg protein is made from the egg white and is therefore fat-free and high in protein. It is considered the most perfect source of protein because it is complete in essential amino acids, branch chain amino acids and glutamic acid. It is completely and easily absorbed by the body. Because of its characteristics, egg protein is used as the standard against which all other proteins are measured. Egg protein should not be used by anyone who has an egg allergy.

Benefits of egg protein:

Highest in the amino acids alanine, arginine, glycine and methine
Fat-free

Rice Protein:
Rice protein is derived by carefully isolating the protein from brown rice. It is a complete protein containing all essential amino acids and nonessential amino acids. Rice protein is hypoallergenic, which makes it suitable for everyone.

Benefits of rice protein:

Hypoallergenic
Suitable for vegans
Complete protein

Soy Protein:
Soy protein provides all the essential amino acids required by us for growth, maintenance, and to deal with physical stress. Of all vegetable proteins, the soy protein amino acid composition is the most complete, and is most like that of high quality animal proteins. Soy protein can also improve the nutritional value of other foods - soy protein contains extra amounts of some amino acids, which can make up for deficiencies in other foods.

Similar to whey protein, soy protein has two types, the concentrate and the isolate, with the isolate being the purer, more expensive form. Soy protein is highly digestible and is comparable to milk and meat as a protein source. Soy protein is ideal for those who have dairy allergies, but should not be taken by those who have a soy allergies.

Whey Protein and Benefits:

Whey contains many similar ingredients in mother's milk, so it's a key ingredient in baby formulas
Whey supplements supply the body with many essential amino acids needed for good health
Whey is used by athletes to repair and build muscles after a tough workout.
Whey protein is a high quality protein that comes from milk. There are 2 main proteins in milk: casein and whey proteins. Whey protein is derived from the process where milk is turned into cheese - the liquid whey is separated from the casein protein.

There are two categories of whey protein powders—concentrate and isolate. The concentrate form is more widely used, easier to find and less expensive. It contains approximately 30 to 85% protein. Whey isolate is a higher quality protein and is, therefore, more expensive. It contains more than 90% protein. Whey isolate is more easily absorbed by the body and contains less fat and lactose.

Digestibility:
Protein digestibility-corrected amino acid score (PDCAAS) is based on a food protein's amino acid content, digestibility, and its ability to supply essential amino acids. The highest possible PDCAAS score is 1.0, and soy protein scores 1.0. Whey protein actually scores the highest at 1.14, but it's reported at 1.0 - the max value allowed by USDA. What this means is that whey scored higher than allowed!

Biological Value and Protein Efficiency Ratio:
Biological value is another measure for protein quality. It measure the amount of protein retained from the absorbed protein, and guess what? Whey protein scored 100 on this, higher than all other types of protein, even soy protein. Another quality measure for protein is the Protein Efficiency Ratio which whey scored near top of all proteins at 3.2 - just below that of egg protein at 3.9. The highest this score, the better the quality.

Straight Protein intake comparison of Whey and Soy:
There are several measures to quantify the quality of a protein, such as Protein Digestibility Corrected Amino Acid Score (I used the short "Digestibility" above), Biological Value, and Protein Efficiency Ratio. Compared to high-end proteins like Whey Protein supplements, Soy Protein falls a little short in most respects - slightly lower in both PDCAAS and Biological value. More prosaic concerns include that it doesn't mix as well, and its taste also falls a little short.

Other factors to consider:
Soy has been identified in several studies as potentially having some positive affects other than just the ingestion of protein. In a recent study, Iowa State University researchers found the consumption of soy protein isolate, or powder, with high levels of isoflavones (plant compounds with a chemical structure similar to that of estrogen) appeared to lessen bone loss in the lumbar (lower) spine of women going through menopause. The group using whey powder lost a significant amount of bone. The whey-powder group had approximately 1 percent lower BMD and the low-isoflavone soy powder group had 0.7 percent lower BMD in the lumbar spine than did the high-iso-flavone group.

For women, excess soy consumption may lead to longer, more painful, and heavier periods.

Whey has been shown to possess immune-boosting capabilities by increasing the body's cellular levels of glutathione, an important anti-oxidant.

Final Thoughts:
The best thing is probably to mix your soy protein powder with some type of whey protein supplement. Either buy a compilation product, or mix a scoop of your favourite soy protein powder with your favourite whey protein. That way, you get *all* the benefits!

Resources:
http://atkins.com/helpatkins/newfaq/answers/WhatIsTheDifferenceBetweenSoyPowderSoyProtein.html
http://meal-replacements.ultimatefatburner.com/soy-protein/soy_protein.html
http://www.bodybuildingforyou.com/protein/Soy-Protein-Powder-Supplements.htm
http://www.bodybuildingforyou.com/protein/whey-protein-supplements.htm
http://www.arthritis.org/resources/arthritistoday/2001_archives/2001_03_04_ResearchSpotlight.asp
http://answers.google.com/answers/threadview?id=346765
http://www.truestarhealth.com/members/cm_archives12ML3P1A8.html

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