In Jain Dharma, an 8‑day fast (Atthai) is a form of anashana—one of the six external austerities (bahya tapa). Done with right faith and discipline, its benefits are mainly spiritual:

• Powerful nirjara: helps shed accumulated karmas, especially by calming anger, pride, deceit, and greed.
• Deep inner purity: steady restraint of the senses and reduction of attachments (aparigraha).
• Stronger samayik and dhyana: the mind becomes steadier for prayer, pratikraman, svadhyaya, and meditation.
• Growth of daya and kshama: increases compassion and forgiveness, culminating in kshamapana.
• Cultivation of equanimity (samatva): less reaction to pleasure–pain, praise–blame.
• Punya: when done without show, with humility and right intention, it yields wholesome merit helpful for the soul’s progress.

How to observe (in brief):

• Take proper pachchakhyan (vow) from a guru or with maryada; maintain boiled water only within prescribed time.
• Pair fasting with maun (measured speech), samayik, pratikraman, alochana–pratyakhyan, svadhyaya, and japa of the Navkar Mantra.
• Avoid display, counting, or comparison; keep inner humility and vigilance over kashayas.
• Break the fast (parna) correctly, at the right time, with gratitude and restraint.

Tradition notes:

• Both Shvetambar and Digambar traditions uphold fasting as a prime austerity for nirjara.
• Shvetambar Paryushan is 8 days; many observe Atthai then. Digambar focus is Das‑Lakshan (10 days); some also undertake 8‑day fasts. The spiritual intent is the same: self‑purification and karmic shedding.

Health maryada:

• If you are ill, elderly, pregnant, or on medication, take guidance and adjust the vow (e.g., boiled‑water fast, ekasan, biasan). Do not risk the body; keep ahimsa to self in view.

The essence: An 8‑day fast is not about endurance; it is a sacred means to purify the soul through right faith, right knowledge, and right conduct supported by tapas.