People who eat high levels of some soy products, including tofu and other so-called "superfoods", may be at an increased risk of memory loss.
Loughborough and Oxford scientists, funded by the Alzheimer's Research Trust, worked with Indonesian colleagues to investigate the effects of high soy consumption in 719 elderly Indonesians living in urban and rural regions of Java.
The researchers' findings, to be published in Dementias and Geriatric Cognitive Disorders later this month, include evidence that a high consumption of tofu is associated with worse memory, particularly among the over 68s.
Lead researcher, Professor Eef Hogervorst of Loughborough University, said: "Soy consumption is on the increase in the West and is often promoted as a 'superfood'. Soy products are rich in micronutrients called phytoestrogens, but it is not entirely clear what their effect on the aging brain is.
"They have similar effects to oestrogen which may offer neuroprotection to the middle-aged and young. but not to over 65s for whom it could heighten risk of dementia and lower memory function."
Intriguingly, the researchers also found that consuming tempe, a fermented soy product made from whole soy bean, is associated with better memory.
Prof Hogervorst said the beneficial effect of tempe might be related to its high levels of folate, which is known to reduce dementia risk.
"It may be that the interaction between high levels of both folate and phytoestrogens protects against cognitive impairment."
Prof Hogervorst cautioned that the effects of tempe and tofu were most apparent in elderly Javanese people, so it is not clear how the findings relate to soy intake among all ethnic groups. An earlier study found that older Japanese American men were also at increased risk of dementia with high tofu consumption.