Life is sustained by food. The mind is however fickle and it is hard to keep it in subjection. The concentration of mind and the control of the constitute (true) asceticism.
आहारप्रभवाः प्राणा मनो दुर्निग्रहं चलम्। मनसश्चेन्द्रियाणां चाप्यैकाग्यं निश्चितं तपः॥