Bhagavad Gita, Chapter 17, Verse 14

Worship of the Devas, the twice-born, the Gurus and the wise, purity, straightforwardness, continence, and non-injury are called the austerity of the body.

Real austerity of the body is defined here through concrete practices, not vague self-denial.

Cleanliness, simplicity, and non-violence are named as the actual substance of bodily discipline. Real definition replaces a fuzzy sense of what austerity even means.