A vegan diet is in effect a fasting diet. When Christians fast, they cut out the "good" stuff, the food that makes life delicious, like butter, meat, dairy, eggs and even fish. So, when not fasting, they eat the good stuff, and when fasting, as a spiritual exercise, they refrain from the nutrient dense foods mentioned above. The fasting diet is also good for you, and is a great detox, but it is not meant to be followed full time, forever. Those who do eventually become quite debilitated, and often sick. You can be a pesco-ovo-lacto vegetarian and still stay healthy, but there has never been a society on earth that was completely vegan. I don't recommend it.