One’s permitted Bittul Torah serves as its foundation:
The Talmud states that at times the nullification of Torah learning is its foundation. What is the meaning of this statement? How can the Issur of Bittul Torah become its foundation? The explanation is as follows: Hashem set up the world in a way that people have to take various breaks in their Torah learning, whether to eat, drink, work for a livelihood and the like. The entire purpose of this break is so one come back to learning Torah with a rejuvenated passion and desire. This is the concept of Ratzo Veshuv. When one becomes temporarily distanced from his lover it creates a stronger desire to cleave to Him.
 Keser Shem Tov 34; Ben Porat Yosef 44a
 Reish Lakish Menachos 99a