For years, soy has been sold as a protein substitute for vegetarians, with the bonus that it can improve heart health and boost brain power. But new research suggests we may need to rethink how soy impacts memory.

The new study from researchers at Stanford shows women over 45 may not improve their overall thinking ability with a soy-packed diet. But it may help them recognize faces.

Over 300 post-menopausal women ages 45-92 were given 25 grams of soy protein daily or a placebo. Each participant was given a memory and cognitive abilities test at the beginning of the study, and then the same tests two and a half years later.

The study found no significant change in test scores between the women who took the soy supplements and those who were given the placebo. There was a small improvement in visual memory, or facial recognition in the soy protein group.

The researchers feel their study offers strong evidence against soy as a brain booster. As always, ask your doctor what's right for you.