I just made the switch from vegetarian to vegan last week. Since then, I've been feeling really weak and a little bit dizzy. Is this normal? My roommates roll their eyes and say, "Well, you're not eating meat or dairy and therefore you have no iron or calcium." That's so frustrating! Does anyone know how long this will last?

That is not normal and your roommates are ill-informed. Please go to Eatright.org (the website of the American Dietetic Association) and search "vegan diet" and then open up the position paper on Vegetarian and Vegan diets. The ADA has long held the position that vegetarian and vegan diets are appropriate and HEALTHFUL for all stages of life, including pregnancy and lactation. The idea that you are missing out on nutrients by not eating "meat" and "dairy" (to use industry euphemisms) is absurd. Not only are not missing out, but meat and dairy are extremely unhealthy and you are making yourself more healthy by abstaining from it. You might help your roommates learn about critical thinking by considering this: does it strike you as a conflict of interest that the USDA--the agency whose job it is to endorse slaughterhouse operations (and we know they are a disaster, as undercover videos show), exterminate all manner of wildlife by virtue of some farmer describing them as "pests," and prop up the cheese and corn industries with subsidies, thus ensuring that Americans eat this junk--should be the agency in charge of telling the American public what and how to eat? I don't think that is a good idea and the USDA will not be advising me on what to eat.

That said, if you not eating wisely, then yes--you may have a reason to feel weak. Sometimes people "go veg" or vegan without the skills or tools to do so. When I first tried it, I gave up the "bad stuff" but didn't know what to replace it with. so I ate vegan "protein" bars (calorie-laden, for sure) and bread. That's how people gain weight and miss nutrients. Don't live on Oreos and chips. Eat a plant-based diet with fresh and organic foods. When you shop, buy fruits and veggies and ingredients--not processed foods out of a box. But you know this. There are plenty of resources to help you eat deliciously, well, and wisely.

Oh, and if a slew of vegan performance athletes, including bodybuilders and ultramarathon runners such as Scott Jurek, can do well on a vegan diet, so can you! Check out No Meat Athlete and ScottJurek.com, to name a few. Don't let people's ignorance derail your intentions.

Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. ~Margaret Mead