Sharing food with colleagues

I have this strange problem. I have had few food restrictions/choices since my early age and owing to this I really don't "prefer to eat" or eat those foods. To explain in detail, we have never had garlic/onion in our curries/stews and it was always in raw form. Also, I am pickle intolerant too, esp those which contain mustard powder like aavakaya. Though I savour hot and spicy food, there are few food choices that I have had all throughout my life and any minor intake of such foods causes upset in the stomach. It happened many a times. And apart from that, I cannot eat sour curds, soury rasam/charu, so even that food intake is limited too. And a few similar food choices that my body doesn't accept.

So, here goes the problem. During school/college days, my group of friends always understood me when I said I cannot eat their food when it contained onion-garlic and life was simple. But now, in the corporate sector where I work, problems seem to crop up. Not a major one. But I want to know how to deal with it.

For example: A colleague gets only aavakaya annam in her lunch box and shares it with me. I told her neatly that I do not eat pickle rice to which she made faces. Next she gets only curd rice and again offers it to me, saying "at my house the curds are not sour, you can have it" and that too with a sarcasm. Another time, when it was onion based curry that she offered and I refused to take it, and again she made a long face.

I have already informed her about my onion intake, curds intake but she seems to be bent on offering and making faces when I decently reject it. I was completely aghast in all those three situations. I am sure, I might encounter such situations where I would be offered food from colleagues and owing to my food choices/restrictions, I might or might not have it. The question is, how do I make it clear to them, without them getting offended or without extending the topic and at the same time not being rude.

P.S: I am not a troll and kindly avoid those comments. And I have already consulted my doc for such food related problems, and I have been strictly restricted not to have those foods which would upset my tummy. I am seriously trying to enhance my social skills. Kindly suggest.

Sharing food with colleagues