Soy Protein Benefits

Research has shown that Asian women who consume large amounts of plant estrogens, especially the isoflavones in soy, have fewer menopausal symptoms and less osteoporosis and cardiovascular disease that women in the West. This has led to increased interest in evaluating soy as a possible alternative for ERT or HRT in women who are either not willing or not able to take these hormone therapies. There are a growing number of studies investigating the potential effects of soy protein on symptoms and other changes that are associated with menopause. Here is a review of the potential benefits soy protein may have to offer.

Soy Protein and Hot Flashes
Of the physical symptoms commonly associated with menopause, hot flashes are perhaps the easiest to measure. Although the hot flush (or hot flash) is the most common symptom of menopause, there is a wide variation in its frequency among women in different parts of the world. In Europe and the United States, 70-80 percent of menopausal women experience hot flushes, in Malaysia 57 percent, in China 18 percent, and in Singapore 14 percent. One of the most striking dietary differences among women in these areas is their intake of dietary soy protein and its phytoestrogens.

In one study by Murkies and associates, postmenopausal women who were regularly experiencing hot flashes were given either soy flour or wheat flour over a three-month period. Although both groups had a decrease in the number of hot flashes they experienced and in their menopausal symptom score, the soy produced a more rapid response.

A recent study by Albertazzi and colleagues in which soy protein with naturally occurring isoflavones was compared with a placebo (casein) in postmenopausal women showed a stronger result. In this study, the researchers found that soy protein was significantly superior to the placebo in reducing the mean number of hot flashes experienced daily. The women taking soy protein had a 26-percent reduction in the mean number of hot flashes by the third week, increasing to a 33-percent reduction by the fourth week, and a 45-percent reduction by the end of the twelfth week.

Soy Protein and Bone Health
Since the prevalence of osteoporosis isn't the same across cultures, researchers are looking to other cultures for clues to possible ways of reducing this disease. Surveys of women in Japan, for example, have raised questions about factors affecting bone health. Although Japanese women consume less calcium than most women in Western countries and are unlikely to use Estrogen Replacement Therapy (ERT) or Hormone replacement Therapy (HRT), they have a lower prevalence of fractures. Some intriguing research in postmenopausal women compared the effects on bone of consuming isolated soy protein with naturally occurring isoflavones or animal protein in the form of casein and nonfat dry milk. In this short-term study the women receiving isolated soy protein increased bone mineral density in the lumbar portion of their spine.

Some researchers believe that part of the answer to this puzzle may lie with the high intake of soyfoods in the traditional Japanese diet. They first looked at the effects of soy protein itself on calcium metabolism. More recently, research has focused on the potential effects of the isoflavones found in soy.

Soy Protein & Calcium Scientists have extended the scope of the research showing that the amount of calcium excreted increases as protein intake goes up. They discovered that not all types of protein have the same effect-protein from animal sources causes much greater calcium loss than vegetable protein. This has been confirmed in a study of 755 Japanese men and women. Researchers found that consuming animal protein was associated with an increase in calcium excretion. However, they found no significant relationship between calcium excretion and the consumption of plant protein.

These findings become more meaningful when they are translated into the effect on bone fractures. As part of the large Nurses' Health Study, researchers looked at usual dietary intake and fracture rates in 85,900 women. First, they compared women averaging less than 68 grams of protein per day with those consuming more than 95 grams. The woman eating more protein had an increased risk of fracturing their forearm. Next, the researchers evaluated the type of protein being consumed. The increased risk of forearm fracture was seen in women consuming animal protein. Consumption of vegetable protein, however, was not associated with an increased risk.

The Isoflavone Story Another area of intense study is the potential effect of soy isoflavones on bone health. Isoflavones are a type of phytochemical, or "plant chemical." The isoflavones found in soy and thus soy protein are genistein, daidzein, and glycitein.


Soy Protein and Cardiovascular Disease
For much of their adult lives, women have a lower risk of heart disease than men the same age. However, once a woman reaches menopause and her estrogen levels fall, her prevalence of CVD rises to equal and finally surpass that of men.

A considerable amount of the research investigating soy protein and its naturally occurring isoflavones has focused on cardiovascular disease (CVD). CVD, which includes heart attack, stroke, and high blood pressure, is the number one killer of American women,

Although CVD represents a major cause of death in many nations, statistics are not uniform in all areas of the world. For example, a look at the most recent worldwide statistics for CVD show that the death rate (number of deaths per 100,000 population) in the United States is 201 for women, but in Japan, the death rate is 99 for women. There are a number of factors that may contribute to such a significant difference. Diet is certainly one of them. In comparing Eastern and Western diets, researchers have turned to the study of soy.

There are two primary ways that soy may protect against the damage done by LDL-cholesterol. Soy isoflavones not only help reduce LDL-cholesterol levels, they also act as antioxidants.

Direct Cholesterol-Lowering Effect Studies in animals and in humans have investigated the cholesterol-lowering ability of soy protein. Significant research has been done to investigate soy protein's effects on LDL-cholesterol and triglyceride levels in your blood. The 1995 New England Journal of Medicine meta-analysis mentioned earlier combined the results of 38 clinical studies evaluating the effect of consuming soy protein on LDL-cholesterol, triglyceride, and HDL-cholesterol levels.

This groundbreaking research showed that consuming an average of 47 grams of soy protein daily: decreased total cholesterol by 9.3% decreased LDL-cholesterol by 12.9% decreased triglycerides by 10.5% increased HDL-cholesterol by 2.4%

The reductions in total cholesterol, LDL-cholesterol, and triglycerides were statistically significant; the increase in HDL-cholesterol was not large enough to be of statistical significance. In the summer of 1995, Dr. James W. Anderson and his associates published a landmark meta-analysis of the effects of soy protein on lipoprotein levels in the blood. (A meta-analysis uses statistical methods to combine the results of a number of smaller studies.) The meta-analysis, which appeared in The New England Journal of Medicine, analyzed the combined data from thirty-eight clinical studies, which together included 730 research volunteers.

It showed that replacing animal protein with soy protein resulted in a 9.3-percent decrease in total cholesterol, a 12.9-percent decrease in LDL-cholesterol, and a 10.5-percent decrease in triglyceride, which is another blood fat associated with CVD. All of these decreases were statistically significant. The individuals who originally had the highest blood-cholesterol levels experienced the greatest degree of cholesterol lowering.

The meta-analysis had two major effects. First, it raised public awareness of soy protein's potential health benefits in CVD. Second, it spurred what has become a steadily increasing interest in investigating soy and soy protein among members of the research and medical communities. The next logical question was: what component or components in soy lowers cholesterol?

All of these studies help show that soy protein with naturally occurring isoflavones lowers blood cholesterol levels, that soy protein without isoflavones does not lower blood cholesterol, and that isoflavones without soy protein also do not lower blood cholesterol.

References
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