4 Cups of What?
As we approach Pesach, we will follow the institution of Moshe Rabbeinu to discuss the Halachos of Pesach beginning thirty days before Yom Tov.
The two Seder nights may be the most complicated and Halachically regimented caloric intake throughout the year. Additionally, the late meal times and the fact that this year, Seder night is preceded by Shabbos, only complicate matters for those who need to carefully monitor what they eat.
Chazal instituted that we drink four cups of wine throughout the Seder. Although they are famously a reference to the four promises of redemption mentioned in Exodus, they also serve to fulfill the dictate to behave as a nobleman, similar to why we lean for the Matzah, and have others pour and serve each other. Accordingly, it is ideal to drink red wine, and if possible, non-Mevushal wine, as that triad is considered the highest quality wine.
If someone is alcohol restricted, it is ok for them to use grape juice. Many Poskim maintain that even if a person just has a hard time drinking wine, it is ok to fulfill the Mitzvah with grape juice.
For someone who needs to monitor their sugar intake, they can water down the wine (or possibly grape juice). Preferably, the mixture should contain 51% wine (including the winery’s dilution), but in extreme circumstances, one can dilute up to ⅔, so long as the liquid retains the taste of wine.
Finally, the amount consumed for each cup can be slightly modified. The volume of Halachic significance is a Reviis. A Reviis is defined as somewhere between 2.5-5 oz. A healthy person should try to fulfill all opinions and drink roughly 5 oz. per cup. However, if needed, one can rely on the more lenient opinions, and use a cup that is roughly 3 oz. One should drink most of that volume (1.5 oz), which is a “cheekful”. One who does this, should be careful to either drink a full Reviis for the last cup, or have someone else make the Bracha Achrona on the wine that is said before Nirtzah.
One should always keep in mind that Halacha may consider some of these patients a “Choleh shyesh bo sakana,” and if so, they should be sure not to put themselves in harm's way to do these special mitzvos. Additionally, there are other mitzvos on Seder night, which are Deorayysa, and one should not jeopardize those by being inappropriately strict on the 4 cups.
Adapted from medicalhalacha.org and from Harav Yosef Berger of Baltimore Shiur