Hi, Tiger
Well, first of all, I don't think that you're eating enough to begin with, which would worry me. Perhaps your coworkers offered the cake to you because they were worried that you aren't eating enough. I might suggest that you eat something with some protien, fats, etc. Of course, I have no idea what your dietary issues are, nor do I know what you need.
I think that a lot of people have an "all or nothing" mentality when it comes to a lot of things, and this can lead to unhealthy notions and behaviors. I think that it's perfectly fine to have one or two sweet things during the course of a day or two...it's just a matter of balancing this out with healthy things that are high in energy sustaining nutrients.
~Colleen