Consuming tempeh can reduce the risk of developing dementia in the elderly, but eating tofu can increase it, said a joint study between universities here and in Britain on Wednesday.
The study between University of Indonesia (UI), Indonesia Respati University, University of Loughborough and University of Oxford said people over 68 years of age who consumed tofu more than twice a day had a worse memory than those who rarely ate it.
But if they also ate tempeh, the risk of dementia was reduced.
"Tempeh consumption very likely offsets tofu's negative associations with memory," Professor Eef Hogervorst of the University of Loughborough said in a seminar on aging and health at UI campus in Depok, where she presented the result of the study.
The study involved 712 respondents from Jakarta, Citengah in West Java and Yogyakarta, with ages ranging from 52 to 99 years.
Sixty eight percent of respondents were women.
Hogervorst said basic soy products, including Indonesian traditional foods of tofu and tempeh, had positive effects on memory because of their phytoestrogen content, which have estrogenic effects.
Estrogen is a female sex hormone. Its blood level is positively associated with memory.
Older women have double the risk of developing Alzheimer's disease, which is the most common type of dementia -- the progressive decline in cognitive function -- because their estrogen levels become much lower than men's after entering the menopause period, Hogervorst said.
She said estrogen worked in various ways to improve memory function, including by improving blood flow to brain, "by modulating neurotransmitter release and receptors, or by acting as anti-oxidants".
Hogervorst said a trial using soy extract showed women administered with the extract right after entering menopause recorded improvements in cognitive activities, including memory and concentration.
Similar affects were recorded with estrogen treatments in recently menopausal women with Alzheimer's disease.
However, she said, if the hormone treatment was applied on women more than 65 years of age, dementia was increased.
"This is a new finding that tempeh can offset tofu's negative effects to memory," Hogervorst said.
"It's perhaps because of tempeh's level of genistein, which is twice higher than that of tofu, or because it contains a high level of folate."
Genistein is an isoflavone or phytoestrogen, while folate or folic acid is the water soluble form of vitamin B9, which is necessary for the production and maintenance of new cells.
Hogervorst said tofu's associations with a worsening memory might be attributed to formaldehyde contents in the soy product.
"The culprit may be formaldehyde but we need further study to confirm this."
Formaldehyde had killed brain cells of rats in a study, she said.
Further nutrients that can reduce the risk of dementia include vitamin B12 and anti-oxidants, but Hogervorst said these were more effective if consumed as part of the diet and not as tablets.
Active people with a higher education were less likely to develop dementia, while smokers and drinkers were in a high risk category, she said.
"Besides those factors, diseases or illnesses like diabetes mellitus, high blood pressure, high LDL-cholesterol, obesity and cardiovascular disease are among things negatively affecting the brain," she said.