The ketogenic diet has become popular in recent years, and is often touted as a way to lose weight quickly. But while the diet may be effective for some people, it can also cause a number of health problems if not done correctly. One such potential issue is vitamin B12 deficiency. Vitamin B12 is essential for red blood cell formation, neurological function and DNA synthesis among other processes in the body and since most sources come from animal products, those following an extremely low-carbohydrate version of the keto diet are at risk of deficiency unless they take supplements or eat foods fortified with this nutrient. Additionally, some medications used to treat epilepsy (a condition commonly treated with the keto diet) can interfere with absorption of this vitamin leading to symptoms like fatigue, depression and cognitive decline that require medical attention. Therefore it's important to speak with your doctor before starting any new dietary regimen so you can ensure you’re getting all necessary nutrients for optimal health.