The Razo, obm.
Iskafya (self-restraint) is not necessarily related to eating and fasting, though it is often erroneously viewed as such.
Reb Zalman Aharon Shneersohn of blessed memory, known as the Razo, was the oldest son of the Rebbe Maharash. He once approached a young man who would afflict himself by fasting, and told him the following analogy:
A community leader lived for several years in a small village, and then moved to another village. Once he came to visit his former residence, in which a public bathhouse had been built shortly before his arrival. He inquired where the funds had originated from, and was told that the means of every member of the community had been assessed, and each was taxed according to his ability. Some paid a great sum of money, but even all the poor paid. The community leader was shown the objects that had been given to the community in lieu of cash.This story was the basis of a whole approach to serving Hashem that was promoted by Reb Shlomo Chaim Kesselman, the great Mashpia in the Yeshiva of Tomchei Temimim (the Chabad Yeshiva) in Kfar Chabad:
The former community leader said to his replacement: “Heed my advice! What you are doing is not right. Those who gave large sums should give an additional amount, as should those of average means, and the poor should be exempted from the tax, because from them you will only receive objects useless to you.”
“The same is true here,” Reb Zalman Aharon said to the young man. “The person is called a ‘small city’ (Koheles 9:14; Nedarim 32b; cf. Tanya ch. 9) and every organ in the body dwells in this city. When one wishes to place a tax, there are wealthy ‘citizens,’ such as thought, speech, the faculty of hearing, and the like. Then there are poor ‘citizens,’ such as the rest of the body, which one would tax by imposing fasts and afflictions. The result of this is that the entire body becomes weakened. Thus, you would be better off leaving the poor organs and demanding a great deal from the wealthy ones: the eyes, ears, mouth, and so on. The results will be far greater.”
Shemu’os V’Sipurim, Vol. 1, p. 271.
Along with Reb Shlomo Chaim Kesselman’s demand for Avodas HaTefillah [prayer at length accompanied by lengthy meditation on Chassidic concepts], he would also demand Iskafya, and some chose to begin with Iskafya in eating. They would eat nothing, and fast for several days. Reb Shlomo Chaim couldn’t stand this.In my own words: True Iskafya involves breaking oneself so that one becomes refined deep down. The effective way of accomplishing this is by focusing on Iskafya in areas related to one’s inner self, instead of sufficing with an Iskafya that is superficially satisfying but in reality totally ineffective, and thus a distraction from one’s true task.
He once told one of the students in Tomchei Temimim [the Lubavitcher Yeshivah] who asked for a path in serving Hashem: “The first thing necessary is Iskafya—but not in eating, for relatively speaking, that is the easiest thing. One should exercise Iskafya in speech, in using one’s eyes, and everything that one desires strongly [“altz voz es vilt zich”], one should not do.
That student responded openly to Reb Shlomo Chaim: “I can’t do that” [the implication is that he felt that he was able to practice Iskafya in eating, but not in the other areas in which he was instructed]. Reb Shlomo Chaim responded, “You are dismissed; you will not be an oived [person who works on self-improvement through Avodas HaTefillah; Reb Shlomo Chaim famously specialized in providing guidance in this area], not today, or ever.” Some say that he expressed of that person, “Even when plants grow on his hand, he won’t be an oived.”
Reb Shlomo Chaim expressed on many occasions: “You want to fast? Do Medrash! Medrash is an acronym for machshovoh—thought, dibbur—speech, re’iyah—seeing, and shemiyah—hearing. Strive to fast in these four areas. Fasts and mortifications break the body but not the evil inclination; in order to fight against the evil inclination one must fast in Medrash. [It goes on to say that Reb Shlomo Chaim would regularly quote the above analogy of the Razo, with slight variations from the way it is written above.]Teshurah L’zecher Reb Shlomo Chaim Kesselman, pp. 32-33.
Clarification: In my humble opinion, I don’t think that this means that one should never excercise Iskafya in eating, because there are clear sources that indicate that one should practice Iskafya in eating (see, for example, Tanya ch. 27). Rather, it means to say that eating should not be the main focus of Iskafya, and perhaps it would constitute much less than it would have in the past. For instance, it might mean refraining from eating two servings of dessert, and sufficing with one, instead of refraining from any, as it might have meant in past times. In any case, the main focus of one’s Iskafya nowadays should be internal.