Magic Beans
Due to their nutritional value and protein content, soybeans can be a great fuel source for athletes.
By Susan Kundrat
Susan Kundrat, MS, RD, CSSD, is President of Nutrition on the Move, Inc., based in Urbana, Ill., and Sports Nutrition Consultant to Northwestern University athletics, Bradley University athletics, and several University of Illinois teams. A former collegiate athlete and the 2003 recipient of the SCAN Excellence in Practice Award for Sports Nutrition, she can be reached at: sk@nutritiononthemove.net
Having grown up in a small Iowa farming community, the soybean has long been a part of my life. Our local economy depended on an up soy market and many of my summers were spent “walking beans,” which meant hundreds of hours trekking up and down rows of bean plants looking for unwanted weeds. I had no idea that I would one day gain a growing interest in the use of soybeans in athletes’ diets.
But my time with the soybean is nothing compared to its own history. References to soybeans date back 5,000 years to ancient China, when farmers grew them as one of their “five sacred grains.” In the early 1800s, they were brought to the United States and initially cultivated just for the production of soy sauce. In the late 1800s, soybeans were also used in cattle feed.
Thanks to the work of George Washington Carver after the turn of the last century, the soybean was thought of as more than animal feed because of its high quality protein and oils. Since then, it’s slowly become a larger part of the American diet, and according to the United Soybean Board, soybeans are now the country’s second largest crop in cash sales and the number-one value crop export.
Due to its nutritional value and an expanding vegetarian market, the variety of soy foods available to consumers has skyrocketed in recent years. And with more and more athletes looking to maximize their nutritional intake, many are wondering how to make soybeans a positive addition to their diets.
BREAKING DOWN THE BEAN
Like most legumes, including dried peas and beans, soybeans are inexpensive and an excellent source of key nutrients. Soybeans, however, provide even more health benefits than other legumes thanks to some additional components in soy. Here’s a quick breakdown of what’s found in the soybean:
Protein: Soybeans are made up of 35 to 38 percent protein. That is higher than most other legumes, which generally contain 20 to 30 percent protein. Even more important is that the protein in soy is ranked as a high-biological value protein, receiving a rating of one (the best possible) from the FDA. That means it contains the protein equivalent of meat and milk. Soy is considered a “complete protein” because all the amino acids needed to form proteins are found in soybeans.
Fat: Soybeans are approximately 40 percent fat, significantly higher than other legumes. However, most of the fat in soybeans is polyunsaturated and monounsaturated fat. It’s a good source of linoleneic acid, an omega-3 fatty acid, which may help decrease inflammation.
Fiber: Soybeans are an excellent source of dietary fiber. Just one cup of green soybeans contains over 10 grams of fiber, which can equal one-third of a day’s goal. Soy foods that utilize the whole bean (such as tempeh, textured soy protein, and soy flour) are also high in fiber. About 30 percent of the fiber in soybeans is soluble fiber, which helps regulate blood sugars and manage lipids.
Calcium: Soybeans provide a good supply of calcium, containing 175 mg of calcium per cup of cooked soybeans. In addition, many soy foods are fortified with additional calcium.
Iron and zinc: Soybeans are a good source of iron and zinc, which are key nutrients for athletes. However, due to the fiber and phytates found in soybeans, these minerals are not well-absorbed.
Isoflavones: Soybeans are rich in isoflavones, plant-derived compounds with estrogenic and antioxidant properties.
ATHLETIC STUDIES
When talking with athletes about protein intake, I inevitably get the question, “Which is better for performance: soy protein or whey protein?” Unfortunately, the answer to that question is not clear cut.
Whey protein is found in dairy products and is a high-biological value protein as ranked by the FDA. It contains all essential amino acids for building proteins and other tissues in the body. Some studies have indicated that whey protein may be utilized better than soy protein by the body for muscle building. But other studies find that both protein sources aid muscles equally.
Don Layman, PhD, Professor of Nutrition at the University of Illinois, has found that the key amino acid for stimulation of muscle protein synthesis is leucine, with whey and dairy foods being the richest sources. “If 25 grams of whey protein are enough to optimize muscle protein synthesis, it will take 40 grams of soy protein and 50 grams of wheat gluten to get the same result,” he says.
In a study of young men completing a 12-week resistance training program published in the Journal of the American College of Nutrition, researchers found a tendency for greater lean mass gains with the consumption of milk compared to soy protein. But the differences were thought to be due to the way the amino acids were delivered to the body, not the differences in amino acid composition.
However, another recent study in the International Journal of Sport Nutrition and Exercise Metabolism, found both soy and whey to be equally beneficial. Twenty-seven young adults participated in a six-week resistance program, with participants ingesting soy, wheat, and carbohydrate supplements. Lean muscle mass increases were the same in the soy- and whey-supplemented groups and both groups saw greater increases compared to carbohydrate supplements.
In the Journal of Nutrition, a recent controlled study examined treadmill-exercised rats that had soy protein and whey protein added to their diets. The rats that ate soy and whey had similar increases in skeletal muscle protein synthesis as those that weren’t fed supplements.
Obviously more research needs to be done in this area. In the meantime, I tell athletes that both whey and soy protein provide great benefits and they should choose whichever one better fits into their diets.
HEALTH IMPACT
Thousands of research studies have documented soy’s relationship to health-related concerns including cardiovascular disease, osteoporosis, and cancer. In 1999, the FDA approved a health claim that soy may be beneficial for reducing cholesterol. While more recent studies suggest that soy is not as powerful as once thought in lowering lipid amounts, its quality protein combined with fiber and key nutrients may have additional effects on cardiovascular health.
Because of their high quality protein, soy foods may have the greatest impact on overall health when used to replace proteins with high saturated fat content. For example, replacing a serving of high-fat meat with a soy-based substitute will benefit overall health with no loss of protein.
However, it’s important to note that much of the research linking health benefits to diets containing soy over the long-term are based on “typical” Asian diets. That means the soy intake is primarily from natural sources of soy (soybeans, soy milk, tofu, tempeh) rather than foods fortified with soy protein or soy supplements.
Based on these studies, the typical recommended intake is 15 to 20 grams of soy protein, or two to three servings of soy foods a day. That actually does not add up to that much soy.
Athletes need 1.4 to 1.7 grams of protein per kilogram of body weight, or 0.6 to 0.8 grams of protein per pound of body weight. That means:
- For a 150-pound athlete (eating 100 grams of protein), soy would make up 15 to 20 percent of total protein intake for the day.
- For a 200-pound athlete (eating 140 grams of protein), soy would supply 11 to 14 percent of total protein.
- For a 250-pound athlete (eating 175 grams of protein), soy would comprise eight to 11 percent of total protein.
Should certain athletes avoid soy for any health reasons? Athletes with thyroid dysfunctions or iodine deficiency should be aware that phytoestrogens in soy may inhibit thyroid function in some people. For those athletes, it’s important to work with a medical professional to determine if this is a concern. In addition, if an athlete has a family history of estrogen-dependent cancer, soyfoods as a staple in the diet may be contraindicated because of the estrogenic properties.
BIG BENEFITS
One of the neat things about soy is that it can help athletes at both ends of the diet spectrum—those who consume little fat but need more protein, and those who get plenty of protein but from fatty products. Even those with a balanced diet can use soy to help improve the timing of their protein intake.
For athletes who are not getting enough protein, adding soy products to the diet can be a big boost. Vegetarian athletes often fit this description. Even vegetarian athletes who incorporate milk products and eggs in their diet may be low in overall protein. Adding soy-based foods can be an easy way to add the extra 15 to 20 grams of protein needed to reach recommended levels. I encourage my athletes to eat soybeans, soy nuts, soymilk, tofu, tempeh, and other natural sources of soy as first options for the greatest overall health benefit.
For athletes who are consuming sources of protein with high fat contents, such as fatty meats or high-fat dairy products, I recommend they switch to soy products. Similarly, I suggest soy products to athletes trying to lose bodyfat. Soy foods like soybeans, soy nuts, and tempeh (which contain both protein and fiber) are good options as they keep athletes satisfied longer and aid in keeping calories low, while supplying needed protein for maintaining muscle mass.
For athletes who have had stress fractures or are at risk for bone problems down the road based on genetics, adding soy may be critical since some studies show soy to have a bone-strengthening effect. Many soy foods (such as soymilk and soy yogurt) are also fortified with calcium and Vitamin D, providing an extra boost. As an added benefit, the calcium in soymilk is easily absorbed.
Another issue to consider is when the athlete eats protein. According to Layman, 65 percent of the protein in American diets is consumed after 6:30 p.m. “You get a three- to five-hour impact on protein synthesis from a meal depending on the amount of protein consumed. Most athletes get plenty of protein at big meals, but they need to focus on getting at least 30 grams of protein at breakfast and lunch,” he says.
There’s no question that many athletes skip breakfast, grab a small lunch, and eat huge dinners after workouts. So developing a simple strategy for helping athletes balance out their protein intake is key. This is where soy can help. For example, a fruit smoothie made with soy or a bagel with soy butter can serve as breakfast, lunch, or a snack. (See “Snack Time” below for more ideas.)
Post-workout protein is also important. The latest recommendations call for recovery fuel with one gram of carbohydrate per kilogram of body weight plus 15 to 20 grams of protein within 30 minutes of a hard workout. Athletes can experiment with both soy and whey protein in recovery shakes and recovery drinks, although I suggest they try whey first since some studies find it to be superior. In addition, they should be looking to get their soy in more natural sources.
If I had to sum up a simple recommendation to athletes on this topic it would be this: Be aware of your protein intake and consider using soy as a source. In reality, the most important message for most athletes is that they need to get enough (but not too much) quality protein in their diet while avoiding excess fat. If soy can help them in this goal, great!
