What is the primary function of Apana prana?

Apana prana is specifically responsible for the downward and outward flow of energy in the body, which is essential for eliminating waste products. This includes not only the elimination of physical waste through the intestines but also the release of toxins and negativity from the body and mind. This function is crucial for maintaining overall health and balance, as effective elimination helps to cleanse the body and allow other processes to function optimally.

In the context of the other choices, while each has its own importance in the broader scope of prana and bodily functions, they do not distinctly define the role of Apana prana. For instance, controlling speech and swallowing relates more closely to other forms of energy associated with upward movement, such as Udana, while regulating metabolism and digestion is a more general function of the digestive system, typically associated with Prana and Samana prana. Pervading the whole body pertains to the all-encompassing nature of prana energy itself, rather than the specific function of Apana. Thus, the choice that best aligns with the unique, targeted purpose of Apana prana is its facilitation of elimination.