Not all who adhere to vegetarian, vegan or other special diets have nutritionally sound eating habits. The clinical consequences of an insufficiently mindful vegetarian or vegan diet include many common symptoms such as anxiety, brain fog, depression, fatigue, insomnia, neuropathies and other neurologic dysfunction. Patients with such symptoms who report having a vegetarian or vegan diet, or a diet that severely restricts meat consumption, require a slightly expanded differential diagnosis. The challenge is to identify which patients require closer attention. This article lists questions to use to quickly assess for potential dietary drivers of clinical symptoms. In many cases, simple nutritional interventions, through diet and/or supplementation, can resolve or minimize problematic symptoms.