How the versatile soybean stacks up as a protein source

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How the versatile soybean stacks up as a protein source

Hypertrophy. It means growth. You already know that protein is the stuff of which muscle is built. Chances are that you're now taking a protein supplement as part of your daily training routine, and perhaps an amino acid supplement, too. And of course you're getting lots of protein from the traditional sources: beef, fish, eggs, chicken, milk . . . and soybeans.

Soybeans? That's right. You're virtually certain to have consumed quite a lot of soy protein. "But that's impossible," you may think. "I just don't eat that much tofu."

Tofu, the Japanese bean-curd preparation, is the only food most of us connect directly with soybeans. And, in fact, it's getting more popular in the US. (The word in the health-food industry is that "Tofu is the yogurt of the Eighties.") Still, unless you're a Japanese, you probably eat lots more chicken and fish.

But the truth is that you probably have also eaten a great deal of soy protein. You may even have been raised on it. Between 10%-15% of babies in the US are raised on a soy-based formula.

If not, you've eaten it in fresh ground beef, processed and canned meat, chicken and fish, convenience food, frozen desserts, diet food, health food - and, of course, in protein powder itself. Many of your favorite protein supplements contain soy protein.

HOW GOOD IS SOY PROTEIN?

What you'll want to know about soy protein is what it does as part of your training diet. Is protein protein? Or is there same fundamental difference between soy protein and the kinds you ingest through other sources?

The Ralston Purina Company of St. Louis - that's right, the Wheat Chex/ Rice Chex people - has done 20 years of research on precisely this topic. You might suspect that Ralston Purina's interest is hardly academic, and you'd be right. The company is the world's largest producer of such protein.

Purina Proteins (the brand name) are called isolated soy proteins. The reason for this is that soybeans in their natural state break down this way:

hulls 5%

oil 20%

carbohydrates 33%

protein 42%

The protein is extracted from the rest of the soybean, yielding a product that is over 90% pure protein, and contains virtually no carbohydrates or fats.

This isolated protein is designed to be added as a supplement to finished food products.

When we're asking how good a protein source is, we're really asking several separate questions. What's its amino acid composition? How digestible is the protein in question? Finally, can it supply enough amino acids to meet human needs? The information you're about to read about soy protein results from Ralston Purina's experiments. Logically enough, the proteins the studies were conducted on were Purina's own.

Let's consider amino acid content. You may know all about the necessity of amino acids. The Food and Nutrition Board (FNB) of the National Academy of Sciences has established requirements for the amino acid content of high quality proteins. These requirements are expressed in milligrams of amino acid per gram of protein. Here's how soy protein compares to the FNB's requirements for nine different amino acids:

	FBN req. (mg/g)	typical soy protein (mg/g)
histidine isoleucine leucine lysine total sulfur total aromatic threonine tryptophan valine	17 42 70 51 26 73 35 11 48	26 49 82 63 26 90 38 14 50

You can see from the table that soy protein exceeds virtually all of the FNB's requirements. It meets the World Health Organization's profile for high quality food sources, too.

What about digestibility? For starters, what is digestibility, and how is it measured?

Digestibility refers to the percentage of a given protein your body retains and utilizes. That percentage is measured in the negative. That is, experimental subjects are given a measured quantity of protein each day. Their stools and urine are then analyzed for protein content, and the resulting figure is subtracted from the amount of protein the subjects started with.

Nevin Scrimshaw and Vernon Young conducted the study reported below on young male adults. They measured the digestibility of soy protein against that of beef, using five different beef to soy protein ratios. In the table below, 0:100 represents all soy protein, and 100:0 represents all beef. True digestibility is the amount of the protein source mixture that was actually absorbed; the second figure is the given mixture's digestibility expressed as a percentage of the figure for the 100:0 all-beef figure.

Beef: soy ratio	% true digestibility	digestibility as % of 100:0 beef to soy (all beef)
0:100 (all soy) 25:75 50:50 75:25 100:0 (all beef)	97.4 98.6 97.8 98.5 97.9	99.5 100.7 99.9 100.6 100.0

In other words, soy protein digests almost exactly the same way beef protein does. Other studies done comparing soy protein with eggs and milk yield similar results.

The last criterion on which to base our evaluation of soy protein is: How efficient is it at supplying the necessary amino acids? The yardstick experimenters used was to determine the amount of various kinds of protein adult volunteers would need to maintain nitrogen balance.

Nitrogen is the chief ingredient of amino acids. Once the body builds up a nitrogen debt, there's no more tissue replacement, no more muscle growth - everything comes to a screeching halt. Researchers compared the amount of soy protein (expressed in grams per kilogram of bodyweight) necessary to maintain nitrogen balance with the amounts of other protein sources.

	amount (g/kg)
soy protein beef 50:50 soy protein: beef mixture milk 50:50 soy protein: fish mixture fish	.75 .72 .66 .64 .59 .55

The studies that furnished the results for the table above were conducted in the United States and Japan. They show fish as the most efficient amino-delivery source, with a fish-soy protein mixture second. Keep in mind that soy protein is virtually always used as an additive to other protein sources.

You want and need to be aware of what kind of fuel is going into your body. It's odds-on that soy protein is one of the protein sources you're already consuming; you may be eating even more of it in the future. Now you know that it is comparable to other high-quality protein sources, although it's not exactly the same as fish, milk or meal. If you're a vegetarian, if you suffer from lactose intolerance, soy protein may now be a major protein source in your training diet. Along with a scientifically regulated intake of fats and carbohydrates and the proper supplementation, it can be part of anyone's nutritional regimen.

Source: Muscle & Fitness