It is clear that both on the Halachic and esoteric aspects of the Torah it is a Mitzvah to embellish in Oneg Shabbos, by eating delicacies and drinking fine beverages, and the concept of sanctifying oneself with that which is permitted does not apply on Shabbos. Nonetheless the above is contingent on that one eats and drinks the delicacies for the right intentions, which is mainly for the sake of fulfilling the Mitzvah of Oneg Shabbos. One who however does not have such intentions, but rather is simply doing so in order to fulfill his animalistic desires, such eating is no better than eating during the week, of which the concept of “sanctify yourself with the permitted” applies. Such a person is considered not to be honoring Shabbos but to be honoring himself on Shabbos. Hence it has been found that Chassidim in general as well as certain Tzadikim would diminish their amount of embellishment contained within their fulfillment of this Mitzvah. One is certainly to avoid over eating if this will refrain him from spending his time in learning Torah, which is the purpose of Shabbos.
 Iskafya is a Chassidic term used to describe self control from indulgent in pleasures.
 For a full analysis on this see Kitzur Hilchos Shabbos Miluim p. 7; Piskeiy Teshuvos 242/3-5
 As explained above in the Shulchan Aruch
 Tanya chapter 7 “One who eats fatty ox meat and drinks tasty wine…., when done for the sake of fulfilling the Mitzvah of Oneg Shabbos and Yom Tov, its divine sparks become elevated.” This is in contrast to during the week that one who eats for the sake of fulfilling his desires descends the Divine sparks to impurity.
The Mitzvah is likewise stated in Igeres Hakodesh 26 “However on Shabbos that there is an elevation of the Kelipas Nogah itself together with the external aspects of all worlds, therefore it is a Mitzvah to eat all the delicacies on Shabbos and to increase in meat and wine, even though that during the week one would be considered a gluten for doing so.” This matter of difference between the eating on Shabbos and weekday is discussed in various Mamarim in Torah Oar and Lekutei Torah. [See Torah Oar Chayeh Sara 15b; Torah Oar Beshalach 65b; Siddur 200-203; Sefer Hasichos 5703 p. 142-146]
In the Mamarim Haketzarim of Admur Hazakein [p. 59] he writes that in essence Shabbos is meant to be a day without eating or drinking, as it is similar to the world to come, however since it is impossible to receive the G-dly pleasure of Shabbos without a physical vessel for this pleasure, therefore one is obligated to eat on Shabbos in order to receive the spiritual pleasure which is contained within it.
 Kaf Hachayim 529/45; Kesav Sofer 107/16 writes that one who does not eat for the sake of the Mitzvah then that meal is considered Seudas Reshus and does not contain a Mitzvah. So is also evident from Tanya chapter 7 from the words “for the sake of Oneg Shabbos”;
Shlah [Shabbos Neir Mitzvah] writes: Those which eat and drink to their hearts content and due to the great amounts of foods fall into slumber are not considered to be pleasuring Shabbos but to be pleasuring themselves on Shabbos.
Sefer Hamamarim Samech Vav p. 154 “Eating on Shabbos is not a physical pleasure but a spiritual pleasure.”; Rebbe in Sichas 1951 Chayeh Sarah 18 states that even the scrupulousness of eating on Shabbos needs a measurement, and that measurement is in accordance to the amount one is scrupulous by other Mitzvos, especially Mitzvos that are painful to accomplish. To note from a story of the Baal Shem Tov who showed his students on Shabbos a man with Shabbos clothes and he appeared like an ox due to his over involvement in eating his meat.
To note also from Mateh Efrayim Alef Hamagen 581/3 which writes that one may delay eating a Shabbos delicacy in middle of his meal, for the sake of Iskafya, and one who does so is considered that he has fasted the entire day.
Reishis Chochmah Shaar Hakedusha 15/53 states: It is proper that one not satiate himself with coarse foods, and he should not fulfill his desires for good foods even on Shabbos.
Elya Raba 293/2 brings in name of Abudarham that one is not to eat too much on Shabbos as this will refrain him from having an appetite for the coming meal. Thus one is to control his inclination and push away the next food even if he desires it.
 So is evident from Ksav Sofer ibid
 Shlah ibid
 Kitzur Hilchos Shabbos ibid states that this is a tradition amongst Chassidim.
 Rav Moshe, the son of the Alter Rebbe would diminish his eating throughout the week including Shabbos and Yom Tov. [Igros Hakodesh Rebbe Rayatz 7 p. 18]; Magid Meisharim end of Bo states that the Magid commanded the Beis Yosef to diminish in eating food even on Shabbos and Yom Tov.
 See Shlah ibid