Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

Dr. David Jenkins (University of Toronto, Canada) addressed the question of statistical significance versus clinical importance with respect to lipid lowering effects of soy (Jenkins 2010). In 22 randomized clinical trials he found an average effect on LDL of approximately 3-5 %, which as such was considered a too meagre result by the American Heart Association Science Advisory (Sacks et al. 2006). Jenkins therefore addressed the questions:

• - What effect size may be considered clinically important?
• - Does soy fit into the clinically important dietetic measures?
• - Could soy contribute additional effects by displacing other food items?

With statins a reduction of LDL values of approximately 30 % can be expected, whereas with combined dietetic measures 20 % can be reached. Consequently, the 5 % achievable with soy protein would correspond to 25 % of the overall dietetic effect, which must already be considered clinically important. If additional factors such as the improvement of inflammation markers such as CRC are taken into account, the overall profile becomes even more beneficial.

In addition, the quote of 3 % improvement indicated by the AHA Science Advisory must be questioned. The latest meta-analysis indicated > 5 % (see contribution of Dr. Anderson), and even these result may be too conservative, as a re-analysis of the data of Anderson shows reductions of 20.9 % when only the studies where the preparation “Cholsoy” was applied are considered.

Soy protein intake will necessarily displace other sources of protein. The replacement of dairy and meat may as such have an additional effect of 3-6 %, which is not necessarily reflected in dietary intervention studies. The “real world” reduction would therefore rather approach 10 %, which further improves the clinical importance of soy protein in the lowering of LDL.

References

Jenkins DJ (2010). Diet versus drugs in chronic diseases: other advantages. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.

Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P and Winston M (2006). Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation 113(7):1034-1044.