Soy's Healthy, but Cholesterol Benefits May Be Minimal

After reviewing the recently published research on soy protein's ability toimprove risk for cardiovascular disease, a 2006 advisory from the AmericanHeart Association (AHA) Nutrition Committee reports only about a 3% reductionin LDL cholesterol with soy protein.

“This reduction is very small relative to the large amount of soyprotein tested in these studies, averaging 50 g, about half the usual totaldaily protein intake,” the committeereports.¹

Additionally, soybean components showed no benefit for HDL cholesterol,triglycerides, lipoprotein(a), or blood pressure, the committee concludes. Asfor soy isoflavones (phytoestrogens), the committee found no effect on LDLcholesterol and other lipid risk factors, and the advisory does not recommendthe use of isoflavone supplements in food orpills.

Yet previous data suggesting soy protein's cholesterol-reducing effectsprompted the Food and Drug Administration (FDA) in October 1999 to authorizehealth claims for foods containing 6.25 g of soy protein, or one-quarter ofthe 25 g needed each day to reducecholesterol.² Asample claim might say, “Diets low in saturated fat and cholesterol thatinclude 25 grams of soy protein a day may reduce the risk of heart disease.One serving of [name of food] provides [number] grams of soyprotein.”

The resulting—and possibly excessive—hype surrounding soy andsubsequent research indicating varying levels of its cardiovascular-relatedbenefit can be confusing.

When looking at the benefits of a food, “it is really critical thatwe look at a large body of research,” says American Dietetic Associationspokesperson Cynthia Sass, MPH, RD, LD, who adds, “no one food is awonder food.”

BODIES OF EVIDENCE

AHA's 2006 analysis evaluates 22 controlled studies on soy protein andsoy-derived isoflavones that have added to the soy knowledge base since thecommittee's 2000 advisory.

In translating the recent findings, AHA Nutrition Committee researcherFrank Sacks, MD, of the Harvard School of Public Health in Boston, suggestsclinicians no longer advise patients that soy protein confers cardiovascularbenefits “since there are minimal if any benefits.”

Like the AHA advisory, a 2005 evidence report from the Agency forHealthcare Research and Quality (AHRQ) also suggests that it takes a heftyconsumption of soy products—a median of 36 g per day, the equivalent ofabout one pound of tofu or three soy shakes—to confer about a 3% netdecrease in LDL cholesterol (5 mg/dl) and about a 6% decrease in triglyceridelevels (8 mg/dl). The report finds no evidence of a significant associationbetween soy consumption and HDL levels, blood pressure, or fasting bloodglucose.³

“Overall, soy was found to have a small effect on lipids,” theAHRQ evidence report states. “It is uncertain whether the results wouldbe sustained,” the report continues, in studies of a longer durationthan those reviewed in the report. About one-third of the studies lasted <6weeks and about one-half lasted <12weeks.³

SO, WHAT IS SOY GOOD FOR?

“Soy still appears to be a very useful food,” says David J. A.Jenkins, MD, PhD, DSc, of the department of nutritional sciences at theUniversity of Toronto, Ontario. Jenkins has researched soy for more than twodecades.

“However much people may pour cold water on the soy protein concept,none of them says it raises cholesterol, and I think all of them, even ifbegrudgingly, would admit that it may lower cholesterol,” he says.Jenkins also suggests that displacing higher-calorie foods with soy protein“may offer an advantage in weightmaintenance.”

As a complete protein containing all essential amino acids, soy can replaceother complete meat, milk, and eggprotein.⁴ “Themain benefit from a cardiovascular perspective is when you substitute soyproducts for meat products,” Sass explains, since doing so lessens one'sintake of cholesterol and saturated fat.

The AHA Nutrition Committee also acknowledges the benefits tocardiovascular and overall health from soy products such as tofu, soy butter,soy nuts, and some soy burgers—all high in polyunsaturated fats, fiber,vitamins, and minerals—when used to replace foods high in animalprotein, which contain saturated fat andcholesterol.¹

“Soybean foods are generally healthy,” Sacks agrees, “butnot superior to other healthy foods.”

Jenkins says including soy protein in the diets of individuals withdiabetes has advantages for kidney and heart health, citing research hecollaborated on with James W. Anderson, MD, and colleagues in the MetabolicResearch Group at the University of Kentucky in Lexington. Anderson's groupsuggests that substituting soy protein for animal protein significantlyreduces hyperfiltration in those with type 1diabetes.⁵ However,the researchers concede that their hypothesis that increasing soy protein mayhave protective effects at all stages of renal function is still underexamination.

Although the AHA and the AHRQ report no significant blood pressure benefitsfrom eating soy protein, a study conducted in China shows that 12 weeks ofreplacing one daily meal with cookies containing 40 g of soybean protein maylower bloodpressure.⁶ Among the302 mildly hypertensive adult participants, those eating soybean rather thancomplex carbohydrate wheat cookies showed a 3- to 4-mmHg greater reduction insystolic and diastolic bloodpressure.

INCORPORATING SOY PROTEIN INTO THE DIET

“Soy products tend to be extremely low [in] or have zero levels ofsaturated fat [and] can still provide overall nutritional benefit,” saysSass.

She suggests using soy-based meat substitutes to replace regular pepperoni,breakfast sausage, ground meats, or bacon; trying nonflavored soy milk inplace of regular milk for baking, on breakfast cereal, in fresh-fruitsmoothies, or in cream-based soups; or snacking on edamame, a whole soybeanproduct becoming popular in restaurants. Those who eat meat may treat soybeansas a vegetable, while a vegetarian or semi-vegetarian would count them as aprotein. “It is one of those foods that can go either way,” Sasssays.

The bottom line when making dietary recommendations, however, is “toemphasize the overall diet and not any one single food” and to realizethat “one healthy thing does not cancel out all the other unhealthythings you eat,” Sass concludes. “Foods work in synergy.... Eachchange you can make to improve your diet is important.” ▪

The Many Faces of Soy Protein

Soy protein is complete, meaning it contains all the amino acids needed inthe human diet. The only plant source of complete protein, soybeans have aprotein quality equal to that of meat and eggs.

The soybean is also a good source of fiber, potassium, folic acid, andother essential vitamins and minerals, as well as fatty acids.

Soy isoflavones are phytoestrogens (plant of human estrogens. Isolatedisoflavones do not always have the same action as isoflavones found in theirnatural state as part of soybeans. The American Heart Association NutritionCommittee reports that soy-based products contain varying amounts ofisoflavones, depending on the processing methodsused.

Soy processing techniques can increase the digestibility of soy proteins,remove indigestible sugars, inactivate enzymes that affect flavor, and preventundesirable changes during storage.

Soy protein comes in three major forms:

1. Soy flour, milled from dried, ground soybeans, is found in commercial bakedgoods and may be purchased for home baking. Soy flour also is processed intotextured soy protein. Its rehydrated form resembles ground beef or groundpoultry and may replace these meats in recipes or food products.

2. Soy protein isolate, used in beverage powders, soups, sauces, energy bars,and some forms of soymilk, generally comes from extracting water and applyingheat to defatted soybean flakes.

3. Soy protein concentrates are made by removing a portion of thecarbohydrates from defatted and hulled soybeans. They take on the flavor ofthe foods they enhance and tend to improve quality because they retainmoisture and hold flavor through multiple cooking processes. Soy proteinconcentrates are used mainly in baked foods, breakfast cereals, and some meatproducts to increase water and fat retention and to improve nutritional values(more protein, less fat).

Water-soaked and ground whole soybeans produce soymilk or a soft,cheese-like soybean curd called tofu. Cooked, mashed soybeans may be fermentedinto miso, a sweet paste used as a flavoring, or tempeh, a solid cake usedsimilarly to meat patties or cubes.

Whole soybeans may be consumed as edamame, steamed for a vegetable serving,or roasted as flavored or plain soy nuts or for creamy or crunchy soy butter.Yellow or black soybeans are available canned or dried.

Source: Soy Foods Association of North America: Soy primer and soy factsheets. Available online atwww.soyfoods.org/health/soyprimer.htmlandwww.soyfoods.org/sales/factsheets.html.Accessed June 9, 2006.