The risk of type 2 diabetes was 40 to 50 per cent lower in overweight women who consumed over 118 grams of soy a day, compared to overweight women who consumed less than 43 grams a day, according to a new study with 25,872 men and 33,919 women aged between 45and 75.
Similar associations were observed when the Japanese researchers considered the isoflavones daidzein and genistein. On the other hand, the risk of diabetes was not affected in men and women in general, according to findings published in the Journal of Nutrition.
“To our knowledge, ours in the first prospective study to examine the association of isoflavone intakes with type 2 diabetes in an apparently healthy population,” wrote the researchers, led by Akiko Nanri from the International Medical Center of Japan.
“[Furthermore,] no previous study to our knowledge has assessed the association between intake of these food factors and type 2 diabetes or glucose intolerance stratified by BMI,” they added.
Nanri and her co-workers used a 147-item food frequency questionnaire to assess dietary intakes of soy product and isoflavone intakes. Over a five year follow-up period, 1,114 people developed diabetes.
While intakes of soy products and isoflavones were not associated with a significant reduction in the risk of type-2 diabetes in men or all women, the highest intakes of soy products were found to significantly reduce the risk of diabetes in overweight women.
In addition, daidzein and genistein intakes of 22 and 36 milligrams per day, respectively, were associated with a 10 per cent reduction in the risk of diabetes in overweight women, added the researchers.
“The possible protective associations of soy and isoflavone intakes among overweight women deserve further investigation,” wrote the researchers.
The study does in no way establish causality, and Nanri and her co-workers note that a potential mechanism is “unclear”. They propose that the oetrogen-like effects of the isoflavones may be behind the benefits, since oestrogen has been reported to affect genes involved in insulin sensitivity and glucose uptake. Beyond the oetrogen-like effects, they note that isoflavones may inhibit the uptake of glucose in the gut, and also improve energy metabolism.
A role for soy protein was also mooted, with previous studies reporting that protein may improve insulin resistance.
The study’s findings were welcomed by soy ingredient supplier Solae. Michelle Braun, PhD, a member of Solae's nutrition science group told NutraIngredients that “Solae is happy to see that a sophisticated analysis led to the findings that soy product consumption was associated with decreased incidence of metabolic syndrome.
“The results of this large, well-conducted study suggest a protective association among overweight women consuming soy. This research further shows that soy has many associated health benefits, including those related to weight management and satiety,” she added.
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are almost 24 million people with diabetes, equal to 8 per cent of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.
Source: Journal of Nutrition
Published online ahead of print, doi: 10.3945/jn.109.116020
"Soy Product and Isoflavone Intakes Are Associated with a Lower Risk of Type 2 Diabetes in Overweight Japanese Women"
Authors: A. Nanri, T. Mizoue, Y. Takahashi, K. Kirii, M. Inoue, M. Noda, S. Tsugane