Only very few people in recent times have attempted and achieved Pi gu in which they learn the trick of drawing in enough natural energy from other sources to sustain the body. I imagine that minerals and vitamins still need consideration. This is where the Heaven Qi and Earth Qi come into your practice.
Since this is a highly esoteric qigong practice, no studies have been done in the West that I am aware of, so very little conclusive evidence exists. However, I don't doubt it for a second. Ancient Buddhist documents describe the same process naturally occurring, without using any qigong technique, at higher levels of meditation practice.
I don't recommend this obviously without close direction by a qualified master.
A study done in China:
http://64.233.161.104/search?q=cache:zjGXIIkA1uUJ:hanlin.hit.bg/bigu_eng.htm+bigu+fasting&hl=en&start=1
From a book on the subject: "Theory of Pi Gu" Chapter
Modern Western theories can't explain Pi Gu. Since Pi Gu is an ancient Chinese practice and philosophy, we should go back to Chinese philosophy and combine it with modern knowledge to understand the theories behind this enduring approach to health maintenance.
In Traditional Chinese Medical Theory (TCM), when we eat food it is transformed into Chi, the vital energy that is stored within the body. No matter what kind of food is eaten, eventually all of it will produce a different kind of Chi and this Chi will then perform different functions within the body. In the universe, there are different types of Chi. But ultimately, no matter how many types of Chi there are in the universe, there are only two kinds of Chi: Yin Chi and Yang Chi.
When we practice Chi Gong, the state of Pi Gu can bring us to a higher level. Chi Gong is practiced so that Chi circulates better through the body. Pi Gu is another form of this practice. In ancient Chinese philosophy, we are told that we can eat Chi instead of food and as a result the body will become stronger. According to mystical legends, many people do not eat for a year and stay alive. In fact, this is possible. In daily life many Chi Gong practitioners can perform this task, not only the old monks and masters. The Chi that is to be consumed is taken from the universe, or it is already stored within the body.
This Chi is not something we can see, but rather something we can feel. It can be compared to the air that can sometimes be felt but never seen.
In daily life we need food to supply us with the required minerals and vitamins. This is a simple common sense approach to good health. However, this wisdom applies when we are in a "normal" state. If we are in a special condition such as the Chi Gong state, we do not need food to achieve a balanced healthy condition and a high energy state.
From the "Fasting" Chapter
Western fasting methods cannot be continued for long because they are not in any way united with Chi. How many people are able to fast one week without any food? But in the Pi Gu state people can last a week, a month, or sometimes a year. Pi Gu is the eastern way of fasting. It can be achieved either through Chi Gong practice or by treatment from a Chi Gong practitioner.
From the "Value of Pi Gu" Chapter
Given the preceding discussion, many people may confuse Pi Gu with simple fasting. Or they will believe Pi Gu is only for weight loss or to clean out the body. Of course it can help the body reduce weight and cleanse the system, but that is not the only purpose. The major purpose is to keep the body in the Chi Gong state so that the body will balance itself automatically.
From the "Going into the Pi Gu State" Chapter
Not ingesting or avoiding food does not mean that you have gone into the Pi Gu state. As we have seen, fasting and Pi Gu have very different feelings. The fasting aspect of Pi Gu relates to the cessation of eating only in a physical sense. However, we must understand the difference between fasting and Pi Gu. When we are really in the Pi Gu state we should not feel hungry while physically feeling more energetic. Another benefit is that the mind will relax and feel more at ease, allowing a better night's sleep.
From the "Full Pi Gu and Half Pi Gu" Chapter
In these modern times, we have so many nutritionists. We like to use a formula to figure out how many calories are needed for daily expenditure, or how many vitamins, magnesium, calcium, and any of the minerals our body needs. But a person in a Pi Gu state can be more energetic and healthier without eating anything, although this does not make sense to most nutritionists. If we follow modern nutritional theories, then Pi Gu is only a fairytale from ancient China. Yet if we face the facts, we can see many people in Pi Gu who do not eat anything for a long period of time. When we think about Pi Gu, we cannot understand or explain how the body gets nutrition from the Pi Gu state. So we should not tie up our mind by science.
From the "The Best Way for Weight Loss" Chapter
In Western philosophy, the major purpose of fasting is to clean out the body and lose weight. Because Pi Gu is so new and is associated with the consumption of food, this leads to confusion regarding the true purpose of Pi Gu. Pi Gu is not limited to the concept of weight loss. It can be related to religion, philosophy, Chi Gong, health, healing, and nutrition. If we only examine it in the context of weight loss, this can lead to a complete misunderstanding of its true value.
