Ngeruh comes from the word keruh, which in Indonesian means ‘impure’. In a spiritual context, ngeruh refers to the impurity of the mind, which, in its ordinary state is clouded by unwholesome thoughts and feelings. Due to the influence of sensual desires the mind dwells in ignorance. From this ignorance a wrong understanding of reality will follow, which, in turn, leads to unwholesome attitudes and unethical behavior. And so, through performing immoral deeds the mind will experience suffering in one way or another. Furthermore, not only the human mind becomes a victim of unwholesome karma, but often this includes animals too.
If one takes into consideration the endless suffering that man has caused his fellow sentient beings during one’s lifetime on this planet, then it becomes quite obvious how much unnecessary pain and torture is caused, either directly or indirectly by oneself. Due to a clouded perception of the nature of reality human beings have acted recklessly toward nature itself and all life forms on this planet. And thus they fell prey to their own lust and greed. This includes the belief that man somehow sees himself as a superior species, and thus they feel free to act according their wishes. In this very way, the insatiable desire for food became an appetite of destruction.
Now, the practice of fasting called ngeruh, aims to restore the balance between oneself and nature. In order to bring back a harmonious relation between the internal and external life energies, the fasting method of ngeruh prescribes a strictly vegetarian diet. During ngeruh one should refrain from eating meat and fish. Nor is one allowed to consume any other animal products (such as eggs, for example). One is, however, still allowed to have more than one meal a day.
Thus, ngeruh can be considered a means to cleanse the impurities in the mind, thereby eradicating the mental defilements that obstruct one’s attainment of the ultimate spiritual goal of the practice.