The Himalayas are well-known as an area for spiritual practice. The weather is very cold there. There are many Gurus in India, so you can see their footprints everywhere. But it's very difficult to find them. Some spiritual practitioners dig an ice cave and live inside without wearing any clothes. Some don't eat anything. The air there is very clean. So by practicing their own methods together with an additional technique, they can go without eating nor do they feel the cold even in winter.
Using good methods of spiritual practice lead to inner cultivation while practicing black magic is external. Whether it's internal or external, what we wear is irrelevant. It would still be external by using a bad method of practice even if we wear nice clothes. It doesn't mean we are cultivating internally if we eat or externally if we don't. Whether one eats or not depends on the situation, for example, when I practiced the Quan Yin Method in the Himalayas, there was nothing to eat nor anything luxurious for me to enjoy. Tolerating this, I was practicing the right way nevertheless. It is the outside path only because one still doesn't truly enter the Tao.