There is no such thing as "transiting" the US. All travelers must formally "enter" the US and are subject to the same requirements whether or not they are connecting to a flight out of the country or not.

I know English isn't your first language, so am unsure if you meant that processed foods are not allowed, which is generally incorrect. Most processed foods, except meat products, are allowed.

In any case, answer the questions honestly and declare any food you have. If you bring in a food item that isn't allowed but declared it, you aren't in any trouble and haven't broken any laws. They'll just confiscate the item.

I cannot answer your question about Brazilian nuts specifically. But if you want them, and your connection allow enough time for secondary inspection, bring them. Just declare them and be able to get at them easily. The customs inspector will know whether or not they're allowed. The very worst thing that can happen is just that they'll take them.