Caitlin,
I concur with what all our fellow vegans are suggesting: primarily, when going to a non-vegan home you can offer to bring something to share, and introduce them to the amazing world of vegan foods.
If you are uncomfortable with the "I'm a vegan...What's a vegan?" discussion, then you don't even have to explain why you are bringing your own dish...pawn it off as a kind gesture you insist upon doing, and then after others partake in your yummy food, you can explain, "By the way, this is vegan."
I find that to be a much more effective way to bring up the discussion on what it is to be vegan. Since their taste buds have already said "this food is good" they will be more willing to listen when you explain why you have a different lifestyle. Otherwise, they'll immediately dismiss you and think (like many others mistakenly think) that vegan foods are boring and tasteless.
Another approach (which is the one I take 95% of the time) is to speak in a language that is understandable for most of the population. I switched to a vegan lifestyle for health reasons after I had my gall bladder removed in February. When the doctor said "no red meat, no dairy, no fried foods..." to me it was silly to try to justify eating chicken and fish when the doctor was telling me cows were bad for me. I made a personal decision to cut everything out...and after it changed my entire body, it began to change my spirit. I am now seeking ways to change other parts of my own life to be kinder to all life.
Certain religions have dietary restrictions (like Islamic or Jewish), and certain individuals have dietary restrictions (diabetes, ciliac disease, etc). So, if I told someone I had to do it, why do they judge me less than if I simply want to do it? Pointing this out to them leaves them with the burden of explanation, not you! :)
8 Comments