How do you combat naysayers who ask things like where do you get your nutrients on a vegan diet?

  neutralize the topic by pointing out that the important thing to understand is whether you are vegan, vegetarian, omnivore, etc. you must--absolutely must-- eat a balanced diet with a wide variety of nutritious foods. Eating meat and dairy does not mean you will automatically meet all your nutritional needs or you'll meet them more likely than someone who eats plants. There are plenty of omnivores with deficiencies, or who are on supplements or have health issues. Meat and dairy are missing lots of key nutrients, too. For example, where is fiber in meat? Where is vitamin C in milk? With any diet, you must eat well and make good choices to be optimally healthy.