Vegetarians and health enthusiasts have known for years that foods rich in soy protein offer a good alternative to meat, poultry, and other animal-based products.
As consumers have pursued healthier lifestyles in recent years, consumption of soy foods has risen steadily, bolstered by scientific studies showing health benefits from these products. In October 2001, the Food and Drug Administration gave food manufacturers permission to put labels on products high in soy protein indicating that these foods may help lower heart disease risk.
As with health claims for oat bran and other foods before it, this health claim provides consumers with solid scientific information about the benefits of soy protein and helps them make informed choices to create a "heart healthy" diet. Health claims encourage food manufacturers to make more healthful products. With soy, food manufacturers have responded with a cornucopia of soy-based wares.
No sooner had FDA proposed the health claim regulation, however, than concerns arose about certain components in soy products, particularly isoflavones. Resulting questions have engulfed the regulation in controversy.
This came as no surprise to Elizabeth A. Yetley, Ph.D., lead scientist for nutrition at FDA's Center for Food Safety and Applied Nutrition . "Every dietary health claim that has ever been published has had controversy," she says, "even the relationship of saturated fat to a healthy diet."
While the controversy may seem confusing to the consumer giving it casual consideration, a careful review of the science behind the rule reveals a strict divide between what FDA allows as a health claim based on solid scientific research and related issues that go well beyond the approved statements about health benefits of soy protein.
What's known is that all foods, including soy, are complex collections of chemicals that can be beneficial for many people in many situations, but can be harmful to some people when used inappropriately. In that simple fact lies much of the scientific dilemma--when do data show a food is safe and when do they show there could be problems?
Scientists agree that foods rich in soy protein can have considerable value to heart health, a fact backed by dozens of controlled clinical studies. A yearlong review of the available human studies in 1999 prompted FDA to allow a health claim on food labels stating that a daily diet containing 25 grams of soy protein, also low in saturated fat and cholesterol, may reduce the risk of heart disease.
"Soy by itself is not a magic food," says Christine Lewis, acting director of the Center for Food Safety and Applied Nutrition's Office of Nutritional Products, Labeling and Dietary Supplements. "But rather it is an example of the different kinds of foods that together in a complete diet can have a positive effect on health."
Much of the research to date has examined dietary soy in the form of whole foods such as tofu, "soymilk," or as soy protein added to foods, and the public health community mostly concurs that these whole foods can be worthwhile additions to a healthy diet. The recently raised concerns, however, focus on specific components of soy, such as the soy isoflavones daidzein and genistein, not the whole food or intact soy protein. These chemicals, available over the counter in pills and powders, are often advertised as dietary supplements for use by women to help lessen menopausal symptoms such as hot flashes.
The problem, researchers say, is that isoflavones are phytoestrogens, a weak form of estrogen that could have a drug-like effect in the body. This may be pronounced in postmenopausal women, and some studies suggest that high isoflavone levels might increase the risk of cancer, particularly breast cancer. Research data, however, are far from conclusive, and some studies show just the opposite--that under some conditions, soy may help prevent breast cancer. It is this scientific conundrum, where evidence simultaneously points to benefits and possible risks, that is causing some researchers to urge caution.
Unlike the controversy surrounding soy isoflavones, available evidence on soy protein benefits is much clearer. That's why FDA limited its health claim to foods containing intact soy protein. The claim does not extend to isolated substances from soy protein such as the isoflavones genistein and daidzein.
"The story's not all in yet," says Margo Woods, D.Sc., associate professor of medicine at Tufts University, who has studied soy's effects in postmenopausal women. "There's a lot of emerging data and it's confusing. In the meantime, we should be cautious." She says her concerns are centered mainly on isoflavone supplements and that she's "much more comfortable" recommending soy as a whole food. "There are probably hundreds of protective compounds in soy [foods]. It's just too big a leap to assume that a pill could do the same thing."
Daniel Sheehan, Ph.D., director of the Estrogen Knowledge Base Program at FDA's National Center for Toxicological Research, also urges caution in consumption of soy isoflavones. In formal comments submitted to the public record of his own agency while FDA was reviewing the health claim, Sheehan, along with colleague Daniel Doerge, Ph.D., wrote, "While isoflavones may have beneficial effects at some ages or circumstances, this cannot be assumed to be true at all ages. Isoflavones are like other estrogens in that they are two-edged swords, conferring both benefits and risks."
As a science-based agency, FDA recognizes that research information evolves with time and that some of the existing confusion will be resolved as new studies are completed. "We continue to monitor the ongoing science," Yetley says. "As new data warrants, we make adjustments in our position and the advice we give to the public. We take this responsibility very seriously."
Soy protein products can be good substitutes for animal products because, unlike some other beans, soy offers a "complete" protein profile. Soybeans contain all the amino acids essential to human nutrition, which must be supplied in the diet because they cannot be synthesized by the human body. Soy protein products can replace animal-based foods--which also have complete proteins but tend to contain more fat, especially saturated fat--without requiring major adjustments elsewhere in the diet.
While foreign cultures, especially Asians, have used soy extensively for centuries, mainstream America has been slow to move dietary soy beyond a niche market status. In the United States, soybean is a huge cash crop, but the product is used largely as livestock feed.
With the increased emphasis on healthy diets, that may be changing. Sales of soy products are up and are projected to increase, due in part, say industry officials, to the FDA-approved health claim. (U.S. retail sales of soyfoods were $.852 billion in 1992 and are projected to rise to $3.714 billion in 2002. See attached chart.) "We've seen this before with other claims FDA has approved," says Brian Sansoni, senior manager for public policy at the Grocery Manufacturers of America. "It brings attention to products; there are newspaper and TV stories and information on the Internet."
To qualify for the health claim, foods must contain at least 6.25 grams of soy protein per serving and fit other criteria, such as being low in fat, cholesterol, and sodium. The claim is similar to others the agency has approved in recent years to indicate heart benefits, including claims for the cholesterol-lowering effects of soluble fiber in oat bran and psyllium seeds.
FDA determined that diets with four daily soy servings can reduce levels of low-density lipoproteins (LDLs), the so-called "bad cholesterol" that builds up in blood vessels, by as much as 10 percent. This number is significant because heart experts generally agree that a 1 percent drop in total cholesterol can equal a 2 percent drop in heart disease risk. Heart disease kills more Americans than any other illness. Disorders of the heart and blood vessels, including stroke, cause nearly 1 million deaths yearly.
FDA allowed the health claim for soy protein in response to a petition by Protein Technologies International Inc., a leading soy producer that tracks its origins to soybean studies sponsored by Henry Ford in the early 1930s. The company was acquired by E.I. du Pont de Nemours & Company (DuPont) in 1997. In considering the petition, FDA reviewed data from 27 clinical studies submitted in the petition, as well as comments submitted to the public record and studies identified by FDA. The available research consistently showed that regular soy protein consumption lowered cholesterol to varying degrees.
One of the studies, conducted over nine weeks at Wake Forest University Baptist Medical Center and reported in the Archives of Internal Medicine in 1999, found that soy protein can reduce plasma concentrations of total and LDL cholesterol but does not adversely affect levels of HDL, or "good" cholesterol, which at high levels has been associated with a reduction in heart disease risk. Another often-quoted study, published in the New England Journal of Medicine in 1995, examined 38 separate studies and concluded that soy protein can prompt "significant reductions" not only in total and LDL cholesterol, but also in triglycerides, another fat linked to health problems when present at elevated levels.
Other studies hint that soy may have benefits beyond fostering a healthy heart. At the Third International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, held in late 1999, researchers presented data linking soy consumption to a reduced risk of several illnesses. Disorders as diverse as osteoporosis, prostate cancer, and colon cancer are under investigation.
Soy's Many Faces
Though soy may seem like a new and different kind of food for many Americans, it actually is found in a number of products already widely consumed. For example, soybean oil accounts for 79 percent of the edible fats used annually in the United States, according to the United Soybean Board. A glance at the ingredients for commercial mayonnaises, margarines, salad dressings, or vegetable shortenings often reveals soybean oil high on the list.
But the health claim only covers the form that includes soy protein. This form can be incorporated into the diet in a variety of ways to help reach the daily intake of 25 grams of soy protein considered beneficial.
While not every form of the following foods will qualify for the health claim, these are some of the most common sources of soy protein:
Tofu is made from cooked puréed soybeans processed into a custard-like cake. It has a neutral flavor and can be stir-fried, mixed into "smoothies," or blended into a cream cheese texture for use in dips or as a cheese substitute. It comes in firm, soft and silken textures.
"Soymilk," the name some marketers use for a soy beverage, is produced by grinding dehulled soybeans and mixing them with water to form a milk-like liquid. It can be consumed as a beverage or used in recipes as a substitute for cow's milk. Soymilk, sometimes fortified with calcium, comes plain or in flavors such as vanilla, chocolate and coffee. For lactose-intolerant individuals, it can be a good replacement for dairy products.
Soy flour is created by grinding roasted soybeans into a fine powder. The flour adds protein to baked goods, and, because it adds moisture, it can be used as an egg substitute in these products. It also can be found in cereals, pancake mixes, frozen desserts, and other common foods.
Textured soy protein is made from defatted soy flour, which is compressed and dehydrated. It can be used as a meat substitute or as filler in dishes such as meatloaf.
Tempeh is made from whole, cooked soybeans formed into a chewy cake and used as a meat substitute.
Miso is a fermented soybean paste used for seasoning and in soup stock.
Soy protein also is found in many "meat analog" products, such as soy sausages, burgers, franks, and cold cuts, as well as soy yogurts and cheese, all of which are intended as substitutes for their animal-based counterparts.
Since not all foods that contain soy ingredients will meet the required conditions for the health claim, consumers should check the labels of products to identify those most appropriate for a heart-healthy diet. Make sure the products contain enough soy protein to make a meaningful contribution to the total daily diet without being high in saturated fat and other unhealthy substances.
Are Consumers Warming Up to Soy?
Although it's clear that Americans are increasing their consumption of soy products, the soybean has a long way to go before it becomes a staple in the average pantry. According to a 1999 survey by the United Soybean Board, two-thirds of consumers surveyed believe soy products are "healthy," up from 59 percent in 1997. While the public may think it's good for them, only 15 percent eat a soy product once a week.
The reason for the disparity appears to be a problem of perception. "Americans are not prepared to make massive lifestyle changes in order to get healthy foods into their diet," says chef and soy cookbook author Dana Jacobi. "Many people have negative attitudes toward soy products due to their misconception of, or their experiences with, taste and texture. But in fact, there are so many ways to work soy into your diet." (See "Adding Soy Protein to the Diet.")
Industry figures show that in some cases, the popularity of soy foods is increasing dramatically. For example, in 1998, sales of soymilk grew 53 percent in mainstream supermarkets and 24 percent in health food stores over the previous year, according to data from Spence Information Services, a San Francisco sales tracking firm. Another research firm, HealthFocus, reports that 10 percent of shoppers in 1998, versus 3 percent in 1996, said they are eating more soy specifically because they believe it will reduce their risk of disease.
According to the Soyfoods Association of North America, three factors are responsible for driving soy's upward trend:
* Baby boomers are more enlightened about, and more interested in, longevity and good health than previous generations.
* The double-digit growth in Asian populations in the United States has fueled demand for traditional soy foods. Americans also are eating more Asian foods, which often include soy.
* Young people are choosing more plant-based foods. A food industry survey found that 97 percent of colleges and universities now offer meatless entrées on their menus.
Mainstream grocery stores also have been prominently displaying soy products amid traditional foods. Soy-based burgers and sausages are often found in the freezer case next to other meats. Some stores offer refrigerated soymilk alongside cow's milk products. And it's not unusual to see tofu, along with soy cheese and cold cuts, in a store's fresh fruit and veggie department. "We expanded our line of soy products in the produce section even before [FDA approved] the health claim," says Paulette Thompson, nutritionist for Giant Food, a large East Coast grocery chain. "But soy is still rather mysterious to many consumers, so it's important to educate them." She says her company is offering information about soy in its Sunday newspaper supplements and its quarterly consumer magazine. It also plans a special "healthy products" promotion that will trumpet the benefits of soy and other diet components.
For consumers reluctant to try soy foods because they fear a bad taste, food manufacturers are creating new lines of soy-based products that contain enough soy to meet the claim requirement but are developed specifically to taste good. "Soy's major stumbling block has been its taste, real or perceived," says Meghan Parkhurst, spokeswoman for Kellogg Co. She says the company plans to introduce in several western states a granola-like soy cereal that got high marks for taste in consumer trials.
Examining the Controversy
While the existing scientific data strongly support the value of increasing soy protein as described in the health claim, questions have been raised about individual components of soy, especially when consumed as concentrated supplements by some segments of the population.
"FDA continues to monitor the debates about the relative safety of these individual soy components and the scientific research that will eventually resolve them," says the Center for Food Safety and Applied Nutrition's Lewis, "If new results suggest an increased risk, the agency will modify or refine its policies in light of the new information."
A number of studies already are under way or in the planning stages now. In one study, Barry Delclos, Ph.D., a researcher at FDA's National Center for Toxicological Research (NCTR), is overseeing a long-term, multigeneration study in rats of the soy component genistein. Early data using rats suggest that genistein alone may prompt undesirable effects such as the growth of breast tissue in males. The study will analyze the relationship between dosage and any adverse outcomes.
The National Institutes of Health is sponsoring a long-term follow-up study on the safety of soy infant formula. The study is a "longitudinal retrospective epidemiological" assessment in which young adults who consumed soy formula as infants will be compared with young adults who consumed milk-based formulas as infants. They will be evaluated for any adverse effects from infancy into their childbearing years.
NCTR's Sheehan says research is needed in this area because an earlier study, published in 1997 in the medical journal The Lancet, showed that infants consuming soy formula had five to 10 times higher levels of isoflavones in their blood serum than women receiving soy supplements who show menstrual cycle disturbances. He says these levels may cause toxicological effects. "Infants receive higher doses of soy and isoflavones than anybody because it is their only food and they are consuming it all the time." The American Academy of Pediatrics, however, has published guidelines showing that in some cases, soy protein-based formulas "are appropriate for use in infants" when cow's milk cannot be tolerated.
Sheehan also expresses concern about the effects soy may have on the function of the thyroid gland. Animal study results, some of which date back to 1959, link soy isoflavones to possible thyroid disorders, such as goiter. A 1997 study in Biochemical Pharmacology identified genistein and daidzein as inhibitors of thyroid peroxidase, which data suggest may prompt goiter and autoimmune disorders of the thyroid. Critics of these studies suggest that iodine deficiency may be a factor that needs to be considered when evaluating study results.
Though the research community has varying degrees of concern about a possible "dark side" to soy consumption, one thread runs consistently through its messages: the need for more research for new uses of soy components. The health claim, however, focuses on uses of soy protein that are generally accepted among health professionals as useful for heart-healthy diets.
Sales of soy foods probably will continue to rise steadily for the foreseeable future, says Sansoni of the Grocery Manufacturers of America. "We're seeing a 'buzz' with soy products that intrigues people and they want to try them," he says. "But I don't believe soy is a fad. It's a continuing trend that's here for the long haul."
With the rising interest, the health claim for soy protein appears to have succeeded. It has provided specific guidelines to help the public improve the heart-healthiness of its diet and has stimulated the industry to produce new food products high in soy protein. These trends, in the end, should be good for those trying to lower their risk of heart disease.
John Henkel is a member of FDA's public affairs staff.