yadā - when; akalpaḥ - unable to act; sva-kriyāyām - in one's own prescribed duties; vyādhibhiḥ - because of disease; jarayā - or because of old age; athavā - either; ānvīkṣikyām - in spiritual advancement; vā - or; vidyāyām - in the advancement of knowledge; kuryāt - one must do; anaśana-ādikam - not take sufficient food.

When because of disease or old age one is unable to perform his prescribed duties for advancement in spiritual consciousness or study of the Vedas, he should practice fasting, not taking any food.