Welcome to TSB
and thank you for caring foryyour little wild creatures.
Now, I know how it can be stressful to see them go about eating things they should not. But... you must remember that squirrels in the wild follow their natural instincts and will go reach for what their little bodies do need. So, yes, they will sometimes indulge and pig out, but their natural instincts will send them back to get the better things they need. I have yet to see MBD among the wilds but I've been around squirrels all my life (and I'm an old lady).
It's true that I also always lived in wooded or suburban areas, never in the city, so maybe other members can chime in on this.
However, re. Brazil nuts, we have had people who had very bad experiences with them and their squirrels - fuzzers who reacted
very badly to them. In such a case, my motto is usually, if in doubt, keep those out. Wilds are not usually thrilled with veggies preferring their own selection, but a lot of mine, foodies you might call them,
love avocados. - errrrr... not cheap.
I usually give mine walnuts, hazelnuts and as a special treat some pecans. I supplement that with sunflowewr seeds and yes - I know some people will cringe here - I do give them peanuts; my backyard is a forest and all my guys are big and fat... so it seems the menu does suit their needs. I have some who have been coming for over 6 years, which is how long we lived here. I can only guess their diet must be fine.
Occasionally I give them a few Cheerios, and roasted butternut squash seeds - which they also love.
What works for mine here may be different than for
city squirrels, butI hope these suggestions can help.