The available studies on the health impacts of soy were limited in number, of poor quality, or their duration was too short to lead to definite conclusions.

Across the 68 studies that examined the impact of soy on cholesterol levels, consumption of soy products resulted in a 5 mg/dL ( about 3 percent ) reduction in LDL and an 8 mg/dL ( about 6 percent ) decrease in triglyceride levels in the populations studied.
Among these studies, a large variety of soy products, doses of soy protein, and doses of soy isoflavones were tested.
The average dose of soy protein in the studies was equivalent to about one pound of tofu or three soy shakes daily.

There was some indication that soy consumption may be more effective at lowering LDL among people with higher LDL levels. Also, larger amounts of soy protein, but not soy isoflavones, are more effective in people with abnormally elevated LDL levels.
Similarly, soy consumption may be more effective at lowering triglycerides among people with higher triglyceride levels; however, there was no evidence of how much soy protein or isoflavones would be needed to affect triglycerides.

Reviews on the relationship between soy consumption and high-density lipoprotein ( HDL ) levels and between soy consumption and blood pressure did not find significant effects.

Among 21 studies evaluating the consumption of soy isoflavones for menopause-related symptoms, there was a net reduction in hot flash frequency ranging from 7 percent to 40 percent, however, these trials were mostly rated as poor quality. Among studies with statistically significant improvements in symptoms, the dose of soy isoflavones ranged from 17.5 to 100 mg/day.

The evidence review completed by AHRQ’s Tufts-New England Medical Center Evidence-based Practice Center also found insufficient data among the 200 human studies examined as part of this analysis to suggest that soy had an effect on bone health, cancer, kidney disease, endocrine function, reproductive health, neurocognitive function, or glucose metabolism.

A wide variety of soy products were studied, including foods such as soybeans, soy flour, soy milk, tofu, miso, tempeh, natto, and okara; isolated and textured soy protein that is added to foods; and soy-derived isoflavone supplements.

Aside from minor gastrointestinal problems reported in some short-term studies, consumption of soy products by study participants was not associated with adverse events.
However, long-term safety data are lacking.

“ This report shows us that there is a lot we don’t know about soy, and that more research is needed to determine if soy has any impact on a number of health conditions,” said AHRQ Director Carolyn M. Clancy.

Source: Agency for Healthcare Research and Quality ( AHRQ ), 2005


XagenaMedicine2005