From The January 2000 Issue of Nutrition Science News
By Linda Knittel
When first introduced, soy foods held a tenuous position in the American diet. The original soy "ice creams" and bland tofu blocks were well received by vegetarians and the gastronomically experimental, yet the general public remained wary of making one of this country's biggest animal feed crops part of the national cuisine. However, as the health benefits of soy evolve from anecdotal reports to sound clinical studies and as soy foods become more accessible, diverse and tasty, Americans are growing quite fond of the lowly bean. Moreover, the October 1999 U.S. Food and Drug Administration announcement that eating 25 g of soy protein a day lowers the risk of coronary heart disease may soon rank soy foods right up there with hot dogs and apple pie.
The soybean is a bright green legume closely related to peas, clover and alfalfa. In addition to containing the cancer-fighting plant estrogens called isoflavones, soybeans are valued for their high protein content, which accounts for nearly 35 percent of their overall composition. This same protein prompted the health claim because it lowers cholesterol and the risk of heart disease. It is easily isolated from the bean's carbohydrates and fats via water extraction and processed into a powder or supplement. The protein is also a low-fat source of all the essential amino acids.
Health claims issued by FDA alert the public to a relationship between a nutrient or substance and a disease or health-related condition (see sidebar, p. 16). "Heart disease is a significant public health issue, and we knew soy could play a role in its reduction," says Georgina Sikorski, director of marketing at Protein Technologies Inc. (PTI), the St. Louis, Mo.-based manufacturing company behind the petition to land soy protein an official FDA health claim.
According to FDA protocol, a private entity must initiate such a labeling campaign. "Even if a product has obvious health benefits, someone has to request a health claim be issued before we will consider it," says Judith Foulke, FDA spokesperson. Thus, in May 1998, PTI submitted a formal health-claim request, along with 20 years of clinical research documentation including 43 human studies.
Of the 43 submitted studies, 27 met FDA criteria for consideration. These 27 studies were clearly presented in English, included information on soy protein intake, revealed blood lipid measurements and were conducted on subjects whose total blood cholesterol counts were less than 300 mg/dL--the number thought to represent the level of the average American.
From these 27 suitable studies, FDA selected 14 on which to base their decision. "Those 14 were the best controlled studies, and their subjects most closely represented the American population," says Foulke. And regardless of whether they examined men or women, healthy individuals, or those with slightly elevated lipid levels, all of the studies had one common element: each clearly demonstrated the cholesterol-lowering ability of soy protein.
Heart-Protecting Soy Protein
An example of such definitive results can be seen in the work of R.M. Bakhit and colleagues at the University of Illinois, Urbana-Champaign. The researchers fed 21 men with mildly high cholesterol a low-fat diet including a daily muffin containing 25 g of protein and 20 g of dietary fiber. The muffins were one of four combinations: soy protein and soybean fiber; soy protein and cellulose; casein, a milk protein, and soybean fiber; or casein and cellulose. After two weeks of eating a straight low-fat diet, the subjects tested each different protein/fiber muffin combination for four weeks at a time. At the end of every dietary treatment, low-density lipoprotein, very low-density lipoprotein and high-density lipoprotein were measured.
Bakhit and his team found that the muffins containing any casein did not have a significant effect on cholesterol. In contrast, the two muffins containing isolated soybean protein significantly lowered total cholesterol levels in subjects whose initial concentrations were greater than 5.7 mmol/L. The result clearly suggests a daily intake of 25 g of soy protein can help prevent heart disease by lowering total cholesterol. 
Similar results were also observed by K.K. Carroll and colleagues at the University of Western Ontario when they compared the effects of protein type on lipid levels in 16 healthy women. In these two experiments, a conventional diet of mixed protein (including animal protein) was compared to one in which protein sources were restricted to soy protein isolates and soymilk. The amounts of carbohydrates and fats in the two diets remained equal. In both studies, which lasted 73 and 78 days, respectively, it was determined that subjects who ate only soy plant protein, rather than a protein combination including animal sources, had significant decreases in their plasma cholesterol levels. 
Considering the volume of clinical data that supports the findings of these two studies, [4,5] as well as the fact that FDA has now issued soy protein one of its rare heart health claims, there is no question that incorporating the nutrient into a low-fat diet can have beneficial effects. But are all soy foods this healthy? According to FDA standards, no. To qualify for the FDA heart health claim, one 8-oz. serving of a soy product must contain at least 6.25 g of soy protein, 20 mg or less cholesterol, 1 g or less saturated fat, 3 g or less total fat, and 480 mg or less sodium--quite a tall order, and one that many soy products cannot fill. Although most soy foods including tofu, soy milk and soy flour have been clinically proven to prevent numerous health conditions, many such products contain too little protein or too much fat to merit a heart health claim.
Benefits Beyond the Heart
Well-read consumers don't need a heart logo on a label to know that soy is a healthy addition to their daily diet for many reasons. Although a few recent studies suggest that for some individuals high soy consumption may pose health risks such as disruptions in hormone balance or interruption of protein digestion, most experts agree that eating 3060 mg of soy isoflavones a day helps reduce cholesterol, eases menopausal symptoms and lowers the risk of some cancers.
According to Regina Lellman, N.D., L.Ac., of the Natural Childbirth and Family Clinic in Portland, Ore., getting the recommended dose of soy can have "practically pharmaceutical-like results." Lellman often prescribes this diet regimen to relieve hot flashes associated with menopause. "Due to their structural similarity to estrogen, soy isoflavones have the capacity to bind to empty estrogen receptors and relieve these hormonally based symptoms," she says.
This ability to decrease hormone reception also seems to be the mechanism by which phytoestrogens including soy isoflavones prevent hormone-dependent cancers such as breast and prostate cancer. To demonstrate this theory, David Ingram and colleagues at the Queen Elizabeth II Medical Centre in Perth, England, conducted a study that included 144 women recently diagnosed with breast cancer and 144 healthy women. Both groups were tested for urine excretion levels of isoflavones and lignans, two types of plant estrogens.  Excretion levels reflect dietary intake of both estrogens--the more one consumes, the more one excretes.
In the Oct. 4, 1997, issue of the Lancet, the Ingram team reported that "for all phytoestrogens, [cancer-free] women had higher median excretion rates." Furthermore, the women who excreted the least amounts of isoflavonoids were four times as likely to have cancer, suggesting that diets high in phytoestrogens significantly decrease breast cancer risk. Similar results have been observed in studies linking phytoestrogens to decreased prostate cancer risk.
Besides lowering their risk of certain cancers, Americans also can look to soy foods as a means of preventing osteoporosis.  Although it remains unclear how soy prevents calcium loss, it appears related to soy's amino acid content. "Soy protein tends to be low in sulfur-containing amino acids, and sulfate compounds may inhibit the reabsorption of calcium by the kidneys, thereby promoting hypercalciuria (excessive calcium loss through the urine)," explains Steven Holt, M.D., in his book The Soy Revolution: The Food of the Next Millennium (M. Evans and Co., 1998). Moreover, an isoflavone-related compound, ipriflavone, has been shown to reduce bone loss in people already suffering from osteoporosis. 
Although heart health, cancer prevention and bone retention may be soy's big claims to fame, the benefits of the bean appear endless. In fact, soy foods promise to help treat everything from alcohol abuse to radiation exposure. [9,10] And while such radical uses may not interest the average American, most could benefit from decreasing their cholesterol. Thanks to FDA's recent ruling, it's now as easy as adding 25 g of soy protein isolate to their morning oatmeal.
Linda Knittel, M.A., a nutritional anthropologist and freelance writer, is the author of All About Treating Depression Naturally (Avery Publishing,1999).
11 FDA-Authorized Health Claims
- Calcium reduces osteoporosis risk
- Sodium increases high blood pressure risk
- Dietary fat increases cancer risk
- Dietary saturated fat and cholesterol increase coronary heart disease risk
- Fiber (fruits, vegetables, grains) reduces cancer risk
- Soluble fiber (fruits, vegetables, grains) reduces coronary heart disease risk
- Soluble fiber (whole oats, psyllium seed husk) reduces coronary heart disease risk
- Folate reduces neural tube birth defect risk
- Dietary sugar increases dental cavity risk
- Fruits and vegetables reduce cancer risk
- Soy protein reduces coronary heart disease risk
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