Vegan for Life - Jack Norris [81]
Heart Disease
Because soyfoods are low in saturated fat, using them in place of meat and dairy can reduce blood-cholesterol levels by as much as 3 to 6 percent. 12 But there is much more to the story about soy and heart health. The protein in soy has a direct effect on blood-cholesterol levels, and simply adding it to the diet has been shown to lower cholesterol levels.13 Moreover, studies of people in the United Kingdom14 and Asia15 have linked higher soy protein consumption to lower cholesterol levels.
Most studies show that it takes as much as 25 grams of soy protein per day (the amount in about three servings of traditional soyfoods) to lower cholesterol, but lower amounts could be beneficial too. The effect is modest—about a 4-percent reduction in LDL-cholesterol—but that can be enough to reduce heart disease risk by as much as 10 percent over time.16,17
The impact of soy is much greater when it is teamed up with other heart-healthy components. The Portfolio Diet is an experimental approach that derives much of its protein from soy and includes plenty of fiber, nuts, and foods fortified with plant sterols (compounds with natural cholesterol-lowering properties). This approach lowers LDL-cholesterol by nearly 30 percent; it’s as effective for reducing cholesterol as some drug therapies.18 Also, soy protein may impact LDL-cholesterol in ways that make it less harmful and less likely to cause clogged arteries.19
And there is reason to believe that soy has other coronary benefits that have nothing to do with its protein or fat content or, for that matter, blood-cholesterol levels. Several Chinese and Japanese studies show that people who consume two servings of soyfoods per day are only half as likely to have heart disease compared to those who consume marginal amounts of soy.20,21,22–23 That’s a dramatic difference—far more than could be due to the cholesterol-lowering effects of soyfoods. These additional protective effects may be related not to protein or fat but to isoflavones, which may directly improve the health of the arteries. 24 Since many people who suffer heart attacks don’t have elevated cholesterol, these additional potential benefits of soyfoods could mean that they offer protection even for people with low cholesterol levels.
Soy and Bone Health
Since estrogen therapy reduces bone loss and fracture risk in post-menopausal women, there has been a great deal of interest in determining whether isoflavones have the same benefits.25 More than twenty-five clinical trials have looked at the effects of isoflavones on bone health, mostly in postmenopausal women.26,27–28 Some have found that soyfoods, soy protein, and isoflavone supplements improve bonemineral density, but others haven’t shown any benefit.
It may be that soy isoflavones simply aren’t protective. Remember that isoflavones are SERMS, which means they don’t always act like estrogen, so they may not have estrogen-like effects on bones. Or possibly the isoflavone supplements used in the studies are less effective than actual soyfoods because compounds sometimes act differently when they are isolated from a food. Here’s one other possible explanation: It could be that a protective effect requires lifelong soy consumption. The clinical studies involved postmenopausal women who typically consumed soy for no more than two years. In contrast, epidemiologic studies of 35,000 subjects in Singapore and 24,000 subjects in China found that women with the highest soyfood consumption—approximately two servings per day—were one-third less likely to fracture a bone.29,30 It is reasonable to presume that these women consumed soyfoods throughout their lives.
Since most soyfoods are rich in protein and many are good sources of calcium, they certainly promote bone health. But whether soy isoflavones add additional protection remains to be seen.
Hot Flashes
Although hot flashes are relatively common among western women as they go through menopause, women in Japan seldom report having them. One reason might be that they benefit from the estrogen-like