The population-based study based in Indonesia found that high consumption of tofu was associated with worse memory, while high consumption of tempe (a fermented soy product) was linked to better memory, according to results published in the journal Dementia and Geriatric Cognitive Disorders.
While the study does support earlier findings from Hawaii (Journal of the American College of Nutrition, 2000, Vol. 19, pp. 242-255), the British and Indonesian researchers indicate that it is unclear whether the potential detrimental effects are due to soy isoflavones or toxic additives like formaldehyde, which is used as a preservative in Indonesia.
Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action.
In addition to their potential benefits for heart and bone health in post-menopausal women, the compounds also been studied for their role in cancer prevention and slowing down the ageing process in peri-menopausal women, and have proved to be a popular alternative to hormone replacement therapy for those wishing to control menopause symptoms without resorting to drugs.
The researchers, led by Professor Eef Hogervorst from Loughborough University, analysed soy intakes in 719 people aged from 52 to 98 from rural and urban settings. Dietary intakes were assessed using food frequency questionnaires (FFQ), while cognitive function was assessed using a word learning test sensitive to dementia.
Tofu consumption was found to decrease memory by 0.18 points, while tempe consumption was associated with a 0.12 increase in memory scores, especially in people older than 68.
Interestingly, increased consumption of fruit was also positively linked to dementia.
Alzheimer's is the most common form of dementia and currently affects over 13 million people worldwide. The direct and indirect cost of Alzheimer care is over $100 bn (€ 81 bn) in the US alone. The direct cost of Alzheimer care in the UK was estimated at £15 bn (€ 22 bn).
By the year 2047, the prevalence of Alzheimer's disease (AD) is expected to quadruple, according to some experts.
Although the mechanism of Alzheimers is not clear, more support is gathering for the build-up of plaque from beta-amyloid deposits. The deposits are associated with an increase in brain cell damage and death from oxidative stress.
The researchers suggest that the phytoestrogens may participate in oxidative stress by promoting the production of cell damaging free radicals.
On the other hand they noted that certain toxic compound such as formaldehyde, sometimes used as a preservative in Indonesia, may be causing the cognitive decline.
"It is unclear whether these negative associations could be attributed to potential toxins or to its phytoestrogen levels," wrote the researchers.
"Tempe contains high levels of phytoestrogens, but (due to fermentation) also exhibits high folate levels which may exert protective effects. Future studies should validate these findings and investigate potential mechanisms," they concluded.
Source: Dementia and Geriatric Cognitive Disorders
2008, Volume 26, Pages 50-57, doi: 10.1159/000141484
"High Tofu Intake Is Associated with Worse Memory in Elderly Indonesian Men and Women"
Authors: E. Hogervorst, T. Sadjimim, A. Yesufu, P. Kreager, T.B. Rahardjo