Many have a custom not to eat nuts during elul, because אגוז is gematria חטא (sin). So what exactly is considered nuts? Almonds, Cashews, Pistachios, Macadamian, Hazelnuts, Pecans? How about Peanuts (or doughnuts)? How to classify?
Even though the famous reason for not eating nuts is because of the gematria, there is another reason not to eat nuts from Elul through Hoshanah Rabbah (and this would apply to all tree-nuts and maybe even peanuts) is since they increase phlegm they will hinder one's own ability to pray and disturb others (by clearing the throat) as well. And since we spend so much time praying at this time of year better to not eat anything that may hinder one's ability to do so. It seems that walnuts and hazelnuts are the only one's mentioned by Mateh Efraim and this is probably because those were prevalent in his area. In addition the word "egoz" is also used as a general term for tree-nuts.