Soy is used to describe products made from soybeans, a legume native to northeastern Asia. For many years, vegetarians have consumed soy products as a way to replace proteins lost by not eating meat. Increasingly, Americans who are not vegetarians also have started to use soy products.

Soybeans can be found in many different foods. About 79 percent of fats consumed annually in the United States contain some form of soybean oil, according to the United Soybean Board. Soybean oil is usually high on the list of ingredients in commercial margarines, mayonnaise, salad dressings and vegetable shortenings.

Historically, the most popular soy products in United States were soy sauce and imitation bacon bits. In recent years, however, the soy industry has created a variety of products that are growing in popularity. There are four soy proteins used when making commercial soy products. Some of these proteins are available in powder, flake or pill form while others are added during production.

Organizations such as the American Heart Association (AHA) and the U.S. Food and Drug Administration (FDA) have issued reports in recent years about the health value of eating a diet rich in soy proteins. Unlike most meats, soy products are low in total fat and saturated fat. In addition, soy products have no cholesterol. Soy is also an excellent source of dietary fiber.

In 1999, the FDA allowed manufacturers of certain soy products to promote the health benefits of soy on their packaging labels. These health claims state that a low-fat, low-cholesterol diet containing at least 25 grams of soy protein a day may reduce an individual’s risk of heart disease. The FDA reviewed 50 human clinical trials as part of the health claim submission.

However, in early 2006, the American Heart Association (AHA) issued its finding from an analysis of 22 studies of the effect of soy on a person’s health. The AHA concluded that contrary to its earlier advocacy of high-soy diets, soy protein appears to have little or no effect on the risk factors associated with heart disease.

Soy is a term given to products made with soybeans, a legume native to northern Asia. Today, most of the world’s soybeans are produced in the United States. The beans grow in a pod, are yellowish brown and resemble the shape of peas. However, unlike other beans and legumes, soybeans are becoming more popular as a food. In addition, soybeans are processed into a variety of products such as cheese, burgers, cereal or milk.

For many years, vegetarians have consumed soy products as a way to replace proteins lost from not eating meat. Soy is an excellent source of protein. Unlike other vegetables, the protein found in soy products is a “complete” protein (a protein that contains all the amino acids essential for human growth and development), similar to the protein found in meats. Soy protein also ranks with egg whites and the protein in milk (casein) as the easiest protein for the body to absorb and use.

Increasingly, Americans who are not vegetarians also have started to use soy products. Organizations such as the American Heart Association (AHA) and the U.S. Food and Drug Administration (FDA) have issued reports in recent years about the health value of eating a diet rich in soy proteins. Unlike most meats, soy products are low in total fat and saturated fat. In addition, soy products have no cholesterol. Soy is also an excellent source of dietary fiber.

In 1999, the FDA granted permission to food manufacturers to advertise the health benefits of soy on soy product packaging. Manufacturers of soy products that meet certain criteria can now place a label on their packaging stating that a daily diet of 25 grams of soy protein may reduce the risk of heart disease. However, recent evidence suggests that the heart benefits of a high-soy diet may have been overstated. For more information, see Ongoing Research.

There are four soy proteins used when making soy products. Some of these proteins are available in powder, flake or pill form while others are added during production itself. The four main protein forms are:

• Hydrolyzed soy protein. The soy protein is broken down into amino acids in a chemical process called hydrolysis. Hydrolyzed soy protein also contains other substances such as monosodium glutamate MSG (MSG). Food products made with hydrolyzed soy protein are not required to list MSG on their nutrition labels. It is a popular taste enhancer in the food industry. It is not considered to be the best source for soy protein or nutrients.

• Soy protein concentrates. Made from defatted soybean flakes, this concentrate is commonly found in frozen soy “burgers.” It contains mainly soy protein (70 percent protein), along with some soy fiber.
  
  
• Soy protein isolate. Manufactured by removing the soy protein from defatted soybean flakes. It contains nearly 90 percent soy protein and is the most highly refined source of soy protein. Soy protein isolate is most commonly used as an ingredient in soy protein bars, soy protein shakes and other soy beverages.
  
  
• Textured soy protein. Products made from textured soy flour, which is manufactured by processing defatted soy flour in an extrusion cooker. Methods for making textured soy protein may vary.

Soy is an excellent source of protein. One-half cup of cooked soybeans has 14 grams of proteins and 4 ounces of tofu has 13 grams of protein. This is about twice the protein found in one large egg or one 8-ounce glass of skim milk, and two-thirds the amount of protein in 3 ounces of lean ground beef.

Unlike animal sources of protein (e.g., beef, chicken), soy contains no cholesterol and very little saturated fat. In addition, soybeans are the only plant source of protein that provides a “complete” protein – a protein that contains all the amino acids essential to human growth and development.

Soy is also high in fiber and rich in B vitamins and polyunsaturated fats. It is rich in essential fatty acids such as omega-3 fats, which are vital to human health.

People who replace even a small amount of their meat protein intake with soy products can achieve a reduction in their intake of calories, saturated fat and cholesterol. There is some evidence that soy foods may help with blood sugar control and may also help lower the risk for some of the possible complications of diabetes.

There is conflicting evidence about the role of a soy diet in helping prevent or reduce symptoms associated with various illnesses and conditions. They include:

• Cancer. The evidence on the relationship between soy and cancer remains cloudy. Some studies suggest that soy components may prevent the growth and spread (metastasis) of cancer tissue and tumors in some areas of the body. There are a variety of compounds found in soy foods with possible anti-cancer activities. However, other studies appear to show that soy consumption may actually raise the risk of some types of cancer by interacting with the hormone estrogen in a negative way. Some physicians now recommend that patients avoid soy if they have certain forms of cancer (e.g., cancer of the breast, ovaries or uterus) as well as those with a family history of estrogen-dependent breast tumors. 
  
  One recent, large study even found that while a soy-rich diet decreases the risk of localized prostate cancer, it may actually increase the risk of advanced prostate cancer. The researchers theorize that this contradictory conclusion may be the result of how tumors change over time. Or, it may result from how soy interacts with different kinds of tumor subtypes.

  Some physicians now recommend that patients avoid soy if they have certain forms of cancer (e.g., cancer of the breast, ovaries or uterus) or if they have a family history of estrogen-dependent breast tumors.

   
• Cholesterol. In recent years, the American Heart Association (AHA) and the U.S. Food and Drug Administration (FDA) have both recommended that people with high cholesterol eat more soy protein on a daily basis. The recommendation followed a number of studies that appeared to find that soy protein intake was found to help reduce blood lipid levels (e.g., LDL cholesterol and triglycerides). Some recent studies appear to back up this claim. Tulane University in Louisiana conducted a study that linked increased soy intake with lower total cholesterol. However, recent studies have cast doubt on the cholesterol-reducing benefit of a diet high in soy proteins. For more information, see Ongoing research.
  
  
• Diarrhea in children. Infants and young children (up to 3 years old) who have diarrhea often experience fewer bowel movements and a reduction in the incidence of diarrhea after switching to soy formula.
  
  
• Menopause. Many women consume soy products or take isoflavone supplements to relieve symptoms of menopause. Research in this area is still in the preliminary stages. However, because soy contains a plant estrogen (phytoestrogen) that is similar in structure to the estrogen produced in the human body, some researchers speculate that increasing the intake of these phytoestrogens could help reduce the severity of menopausal hot flashes.
  
  
• Osteoporosis. Many soy products contain calcium and isoflavones, both of which have been associated with reducing the risk of osteoporosis. However, not all soy products are good sources of calcium. The AHA recently stated that evidence of soy’s power in preventing or reducing risks of osteoporosis appears to be mixed. 
  
  In fact, a recent study found a strong link between consuming soy protein supplements and reduced bone loss in nonobese, postmenopausal women. However, not all soy products are good sources of calcium. In addition, the AHA recently stated that evidence of soy’s power in preventing or reducing risks of osteoporosis appears to be mixed.

Researchers continue to study the health effects of soy foods. The following are some of the possible health benefits of soy, although further research is necessary before a recommendation can be made:

• Reduce high blood pressure
  
  
• Prevent the growth of cancer tissue and tumors in some areas of the body
  
  
• Maintain bone density
  
  
• Strengthen the immune system
  
  
• Control blood sugar levels in diabetics
  
  
• Reduce inflammation

Certain bacteria found in the intestines that promote better health (probiotics) can be found in some unpasteurized and fermented soy products. Probiotic foods contain these friendly bacteria and help protect these bacteria from stomach acids and other unfriendly bacteria.

Probiotics may produce several desirable effects in the body, including helping to control cholesterol levels, manufacturing vitamins, acting as an anti-carcinogenic (cancer) agent, relieving symptoms of anxiety, enhancing bowel function, and recirculating hormones (like estrogen) back into the bloodstream.

There are many different components in soybeans that are being studied for possible health effects. These components and the proposed health benefits include:

Soybeans can be found in many different foods. About 79 percent of fats consumed annually in the United States contain soybean oil, according to the United Soybean Board. Soybean oil is usually high on the list of ingredients in commercial margarines, mayonnaise, salad dressings and vegetable shortenings.

Soybeans are available in the pod and removed from the pod. Soybeans in the pod are sold both fresh and frozen and are cooked in the pod and eaten as a snack in the form of edamame. Soybeans removed from the pod may be fresh, dry, canned or frozen and are often used in soups, stews and casseroles.

Historically, the most popular soy products in United States were soy sauce and imitation bacon bits. In recent years, however, the soy industry has created a variety of products that are growing in popularity. They include:

• Egg replacers. Made from potato starch and lecithin (a soy-based product).
  
  
• Miso soybean paste (fermented). Often found in Japanese cooking. Can be used as a condiment or mixed with dips, sauces and soups. Miso has protein, calcium, and a small amount of B vitamins. Miso is normally high in sodium. A low-sodium version of miso is available.
  
  
• Meat analogs. Products that resemble meat, but instead have been made from soybeans. They include soy hot dogs, sausages, bacon and burgers.
  
  
• Soy yogurt, cheese and sour cream. Soy yogurt is made from soy milk with live bacteria added. Soy cheese is also known as tofu cheese. It is very low in fat and cholesterol-free.
  
  
• Soy flour. Made from roasted soybeans that have been ground into a fine powder. Provides more protein and fewer carbohydrates than wheat flour, and no gluten. Because of the lower gluten factor it may be necessary to mix soy flour with other types of flour during baking and cooking.
  
  
• Soy grits. Similar to soybean flour, except the soybeans have been toasted and cracked into small pieces. Grits are available in different consistencies including coarse, medium and fine.
  
  
• Soy milk. Non-dairy, made from crushed, cooked soybeans. Provides a good source of protein but it has less calcium than cow’s milk. Supplementation may be needed. Some forms of soy milk may or may not be fortified with vitamin A and vitamin D, or with calcium. Soy milk is commonly used by people who are lactose-intolerant.
  
  
• Soy mayonnaise. Usually made with tofu. The ingredient label will state if the product is made with eggs.
  
  
• Soy nuts. Soybeans that have been soaked in water and then backed or roasted until lightly browned. Crunchy, roasted snack that resembles peanuts.
  
  
• Soynut butter. Product similar to peanut butter, but made from soybeans.
  
  
• Soy oil and margarine. Unsaturated fat extracted from soybeans. Soy is also the source of the most commonly available form of vegetable oil.
  
  
• Soy sauce: Derived from fermented soybeans and water. Soy sauce is not a significant source of protein.
  
  
• Tempeh. Soybeans mixed with rice, millet or another grain and fermented into a soybean cake. It has a smoky or nutty taste and is used to flavor soups, casseroles, chili or spaghetti. It can also be grilled or marinated. It is an excellentsource of protein and rich in calcium.
  
  
• Textured soy protein. Also known as TSP, it is a soy flour that is high in protein and often sold as granules, flakes or chunks. TSP is used to replace or extend meat and poultry or to produce vegetable burgers or sausages.
  
  
• Tofu. Also called soybean curd, it is made from curdled soybean milk. Tofu is an excellent source of protein. Some forms of tofu are calcium fortified, indicated on the label as “calcium sulfate.” Tofu takes the flavor of whatever it is prepared with and may be used in pizza, soups, sauces, dressings, chili or stir-fry cooking.

Tofu is also offered in many different flavors, including smoked, teriyaki, Mexican and Italian. Unpackaged tofu or tofu packed in water needs to be refrigerated and used within a week. If it is kept in water, the water should be changed daily. Tofu in aseptic packaging dose not require refrigeration until it is opened. Tofu can be frozen for up to three months.

While eating moderate amounts of soy (such as the 25 grams of soy protein per day outlined in the U.S. Food and Drug Administration [FDA]-approved health claim) is considered safe, some scientists are continuing to study soy to identify health effects.

When choosing soy products, people are urged to look at the ingredient label to better detect the levels of protein and other ingredients that are present. Not all soy products contain the same amount of proteins. Generally, soy protein isolate – which is added to many soy food products – has the highest level of protein. It is followed in order by soy flour, whole soybeans and tofu.

Soy supplements sold in tablets and capsules are widely available and are generally composed of concentrated soy isoflavones. Most experts agree it is better to consume soy foods than to use soy supplements.

As with all foods, soy has beneficial effects for many people but can be harmful in certain situations for others. Some people who start eating soy products may experience stomach upset or digestive problems such diarrhea and constipation. Typically, this passes as a person transitions to a soy diet or reduces a high amount of soy in the diet.

There has been speculation about other health risks associated with soy protein. Most of these concern focus on specific components of soy such as isoflavones rather than on the whole food or the soy protein. Isoflavones are phytoestrogens, a weak plant-based form of the hormone estrogen that may have an effect on the body that is similar to a medication. This effect is most likely to occur in postmenopausal women. However, the data is mixed. While some research suggests that high levels of isoflavones may lead to cancer, other research suggests that such levels may actually prevent cancer.

Most experts agree that a moderate soy intake, such as the 25 grams of soy protein a day outlined in the U.S. Food and Drug Administration (FDA)-approved health claim, is generally considered safe. However, it is important to note that FDA has limited claims about the health benefits of soy to foods containing intact soy proteins. The long-term health effects of other isolated substances from the soy protein or from eating larger quantities of soy are still under investigation. Any concerns about adding soy to the diet can be discussed with a physician.

There has been some confusion about the fact that soy products have only been granted GRAS (generally recognized as safe) status by the FDA for limited industrial use as binding glue for cardboard, not as a product for human consumption. Although this is true, other common foods have also never been granted GRAS status. The general opinion of the medical community is that soy products are safe.

There is no convincing evidence that moderate soy protein consumption has an adverse effect on thyroid function in healthy humans consuming adequate amounts of iodine. Early research identified that soy, in addition to a number of plant-based foods, may contribute to the formation of a goiter, an enlargement or swelling of the thyroid gland. But there is no risk of goiter in healthy people consuming soy products if they are not deficient in iodine.

Patients who are watching their weight should be aware that soy foods do contain moderate amounts of fat. However, most of the fat is unsaturated and does not contribute to clogged arteries. In addition, low-fat soy products often are available.

In recent years scientists have begun to question whether the use of soy infant formula may positively or adversely affect a child’s long-term health. Soy-based formula is an alternative to cow’s milk formula that may be used in children who need to avoid cow’s milk or milk sugar (lactose) for medical reasons. Researchers have examined the levels of isoflavones found in the blood of infants on soy formula. It is not known if levels of isoflavones in the blood of babies who use soy formula cause any biological effects. Further studies are underway to determine if these effects are positive or negative.

Some children who use soy formula experience vomiting, diarrhea, growth failure and damage or bleeding of the intestinal wall. However, this is rare. It is important to note that for infants who are allergic to dairy formula and/or cannot be given breast milk, soy infant formula can be life-saving.

In the late 1990s, the U.S. Food and Drug Administration (FDA) reviewed the findings of 50 clinical trials related to the effects of soy protein on the levels of total cholesterol and LDL cholesterol in the blood. As a result of that review, in the fall of 1999 the FDA approved a health claim on soy protein’s ability to reduce the risk of heart disease within the context of a low-saturated fat and low-cholesterol diet. The approval means that manufacturers may use the following statements (or one reasonably similar) to market certain soy products:

“Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease. One serving of (name of food) provides ___ grams of soy protein.”

OR

“25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of [name of food] supplies ____ grams of soy protein.”

To qualify to use this health claim, the food in question must meet the following FDA criteria. Per serving, the product must have:

• At least 6.25 grams of soy protein
• Less than 3 grams of fat (low fat)
• Less than 1 gram of saturated fat (low saturated fat)
• Less than 20 milligrams of cholesterol (low cholesterol)
• Less than 480 milligrams of sodium in an individual food, less than 720 milligrams of sodium if considered a main dish and less than 960 milligrams of sodium if considered a meal.

Foods made from the whole soybean (instead of soy protein) such as tofu can qualify for the health claim if the product has no added fat. These would include soy foods such as tofu, soy milk, soy-based burgers, tempeh, and soy nuts.

According to FDA research, diets with four daily servings of soy can reduce levels of low-density lipoproteins (LDLs, the so-called “bad proteins”) by as much as 10 percent. Heart experts agree that a 1 percent drop in total cholesterol can equal a 2 percent drop in heart disease risk.

The American Heart Association (AHA) has been among the organizations touting the health benefits of including soy in a person’s diet. However, in early 2006, the AHA issued its finding from an analysis of 22 studies of the effect of soy on human health. The AHA concluded that contrary to its earlier advocacy of high-soy diets, soy protein appears to have little or no effect on the risk factors associated with heart disease. The organization reported that eating large amounts of soy protein appears to reduce low-density lipoproteins (LDLs, or “bad” cholesterol) by just 3 percent.

The AHA analysis also raised doubts about other health benefits that have been associated with soy. For example, it found that evidence of soy’s power in preventing osteoporosis appears to be mixed, and that there was no strong evidence that soy relieves symptoms of menopause.

Nonetheless, the report concluded that soy products still offer potential health benefits to consumers because of their high content of polyunsaturated fats, fiber, vitamins and minerals. They also have low levels of saturated fats and can be used to replace meats with higher levels of these fats.

Other new research continues to investigate possible links between soy intake and improved health. One recent study found that a natural substance made from soy offered significant health benefits when give to animals with a disease similar to multiple sclerosis. Animals who received the substance shoed dramatic improvement in their ability to move and walk

Preparing questions in advance can help patients have more meaningful discussions regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions related to soy:

1. Is soy safe for me to include in my diet instead of meat?
   
   
2. If I am anemic, can I eat soy products everyday?
   
   
3. Is soy safe for me while I am taking hormones?
   
   
4. If I include soy products in my diet, can I stop taking my cholesterol-lowering medicine?
   
   
5. Is it possible to eat too much soy?
   
   
6. What does the latest research say about soy products?
   
   
7. Is it safe to eat soy while I am pregnant?
   
   
8. My family has a history of breast cancer. Does this affect how much soy I can eat?
   
   
9. Is it safe for my children to eat soy products every day?
   
   
10. There appears to be growing controversy about how beneficial soy is to a person’s health. What is your belief?