Bhagavad Gita, Chapter 6, Verse 16

Success in Yoga is not for him who eats too much or too little, nor, O Arjuna, for him who sleeps too much or too little.

Real discipline doesn't mean extremes, it means genuine balance in the ordinary basics.

Krishna gets practical here, not abstract. Neglecting the body through overindulgence or excessive denial both get in the way of the same goal, moderation isn't a lesser path, it's a real requirement.