Interesting about the foods! My lo is 8months and I find that I have to be VERY careful about what foods I'm giving her in combination, because she gets constipated very easily (so cereal only with plums, not with apples, etc...) and then the constipation makes her cranky.
Fortunately, she has a lot of mobility, but I do find her getting frustrated with things like wanting to take the spoon for herself, then dropping it, then being upset because she wants to eat off the spoon, etc. She REALLY wants more independence.
When I have to step out of the room, I do not necessarily go to her if she is whining/complaining, but of course if it's a distress cry I hustle. However, I do acknowledge that I hear her by calling out to her, "yes, ma'am, I hear you, I'll be right back, mommy's going potty" or whatever. That seems to keep it from escalating.