Blog Directory - Blogged foodliterate: A Perfect Score

Tuesday, November 6, 2007

A Perfect Score

As I discussed in my last post, proteins are assembled from amino acids, and there are 9 essential amino acids our bodies require. Essential amino acids are those that our bodies cannot produce itself and so must be obtained through the foods we eat. Complete proteins contain all of the essential amino acids our bodies need and are considered high quality proteins. For those of you who are seriously interested - this is a great online book on proteins.

You see, the catch is that all of the amino acids needed for protein synthesis in your body must be in the cell at the same time, your body can't store seperately and put them together later. If you don't eat all the essential amino acids in the same meal, or a complimentary set (think beans & rice), your body will break down your muscles to obtain the missing amino acids. Not good. This is why essential amino acids are so important, their content determines the quality of a protein.

There are a number of ways to measure a proteins quality, but none of them are perfect measure of a proteins efficiency/digestibility. Here are the most common:

Bioavailability - the degree to which a substance can be digested and utilized by the body in the amount and form in which it is present.

% Biological Value (% BV) - the proportion of absorbed protein (Nitrogen balance) that is retained in the body for maintenance and/or growth.

Casein (milk protein) = 85% Whey Protein Isolate = 98% Soy Protein Isolate = 80%

Rice Protein = 64% Whey Protein Concentrate = 95% Whole Egg = 100%

Net Protein Utilization (NPU) - the proportion of protein intake that is retained; a completely digested protein would have an equal %BV and NPU value.

Casein = 76 Whey Protein Isolate = 92 Soy Protein Isolate = 61

Rice Protein = NA Whey Protein Concentrate = 93 Whole Egg = 94

Protein Efficiency Ratio (PER) - based on the weight gain of a growing test animal (rat) divided by its protein intake over a study period (usually 10 days).

Casein = 2.9 Whey Protein Isolate = 3.5 Soy Protein Isolate = 2.1

Rice Protein = 1.3 Whey Protein Concentrate = 3.0 Whole Egg = 3.8

Protein Digestibility Corrected Amino Acid Score (PDCAAS) - a method of comparing protein quality based on the amino acid requirements of humans (a score of 1.0 = a complete protein, i.e. 100% of the essential amino acids after digestion).

Casein = 1.23 Whey Protein Isolate = 1.14 Soy Protein Isolate = 0.92

Rice Protein = 0.55 Whey Protein Concentrate = 1.0 Whole Egg = 1.19

So, does anyone really pay attention to these values? A few do, (body builders, olympic atheletes) but most of us don't. Does this have any practical applications? Can you use this info? Well sure. If you happen to like protein bars, you can use this information when looking at the nutrition panel to determine the quality of the proteins it contains. If you are a vegetarian/vegan, you can use this information to make sure you are getting a complete compliment of proteins in each meal so your body doesn't feed on itself. And you can impress people at the gym with your newly acquired expertise on this topic! Ok, maybe that's just me.

So, what's next you ask? Well, you know what a protein is and you know how to judge their quality, so how about what it is they do in the food products you purchase? In my line of work we are far more concerned with the properties different proteins exhibit and I will tell you all about it in my next post.

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