Balance is the Key
It is important to note that certain balance between all three guans is important for healthy and balance life. Therefore a tamsic food or tamsic activity is not necessarily bad and sometime may be required to treat certain disease or imbalance in life e.g. garlic comes under tamsic food but we use it as a medicine for treating vata disorders.
stavam rajstam iti guna parkritisambhava nibdhanti mahabhaho dehe dehynamvyama
(Bhagavad Gita 14/5)
In this shloka of Bhagwad Gita, lord Krishna says that atma is bound to the body through three gunas (the driving forces behind physical manifestation of existence) – sattva, rajas, and tamas. The same concept is explained in ayurveda as human life consisting of the sharira (body), indriya (faculties of action) and manas (mind). Interaction among the sharira, indriya, and manas becomes the cause of knowledge about anything.