I am a strict vegan - I don't eat anything that comes from animals, including milk and eggs - and I'm from an Ashkenazi background. During Pessah I can barely nourish myself without kitniyot (legumes). Can't there be an exception made for people like me? The subject of kitniyot is the Pessah land mine. The range of halachic opinion oscillates between completely permitted (the classic Sephardi custom) and stringently prohibited (the Ashkenazi counterpart). Regarding the Sephardi custom, a comprehensive overview can be found in the responsa of Rabbi Ovadia Yosef, in which he endorses the heter (permission). However, it is worth noting that some Sephardim prohibit rice and that the Moroccan custom is to prohibit kitniyot that were stored in sacks (such as rice and chickpeas).
Read the complete Pessah 5767 Supplement
The issue of kitniyot first arises in the Jerusalem Talmud (Halla 1:1) with regard to rice. The minority opinion of Rabbi Yohanan ben Nuri is that rice ferments. Although this view appears to be refuted in the Babylonian Talmud (Pessahim 35a and 114b), a few opinions hold that one should be stringent like Rabbi Yohanan, making rice and its derivatives a real hametz hazard. The classic Ashkenazi view, championed by the Semak (13th century, France) and others, is that the stringency is a custom rather than an issur (clear-cut halachic prohibition), and developed due to two primary cautions:
1. The similarity between flour produced from the five grains and the flour made from kitniyot.
2. An all-too-likely possibility of the different grains getting mixed up, either due to the same sacks being used for storage or to consecutive harvests.
The problem with minhag (custom) is that, counter-intuitively, it is sometimes harder to halachically maneuver around a minhag than it is around an issur that has a clear reasoning behind it. Customs derive their authority from what the community is "doing at the moment" and not from the coherence of the original argument. Accordingly, there is little one can do to relieve you of your culinary stress on Pessah.
A disclaimer before we continue: The above does not apply to the elderly, babies and people who are on a specific diet for health reasons. In these circumstances, kitniyot are permissible due to the halachic concept of pikuah nefesh (the imperative of saving life). Moreover, at a time of "extreme need" - for example in a time of famine - kitniyot were entirely permitted by the Hatam Sofer (19th century, Bratislava).
Do not panic yet, help is at hand. Rabbi Moshe Feinstein (20th century, America) claims that peanuts are not considered kitniyot (despite the above reasoning being applicable), because they were not used in Europe when the kitniyot custom became pervasive throughout Ashkenazi communities. He explains that one is not allowed to extend a custom that developed specifically around certain details. Unlike decrees or classical halachot, where it is possible to extrapolate the guiding principles and reapply them, customs that developed bottom-up are restricted purely to their specifics.
Expanding Feinstein's reasoning beyond the confines of his specific answer regarding peanuts, the same would apply for sweetcorn and all forms of soy and tofu (providing that no hametz enzymes are involved in the production process). Unfortunately the mainstream has not adopted this opinion.
However, in a situation like yours in which one has a specific diet, it seems reasonable that we would be able to apply Feinstein's heter. This is essentially a halfway position which expands the definition of "need" to include cases of diets based on healthy lifestyles or ethical concerns, while still preserving the stringency of kitniyot in its classical form, as it appears in the medieval Ashkenazi communities, as opposed to its development in recent centuries.
Additionally, a popular seed that has gained currency in recent years is quinoa. Although it is very similar to rice, quinoa is technically a grass (from the goosefoot family cultivated in the Andes) and therefore is not classified as kitniyot. While I am not recommending indiscriminate consumption of quinoa, you might want to check the feasibility of incorporating it into your diet.
A final disclaimer: My working assumption has been that you grew up religious and are an old-timer with the Halacha. If you are a newcomer and are gradually getting acquainted with keeping the mitzvot and a halachic way of life, kitniyot is not the place to start.
Beyond that, I suggest marrying a Sephardi or endorsing the popular saying: "Eat healthy, exercise well - die anyway." Alternatively one could always start eating meat. (P.S. The writer is a vegetarian).
The writer studies in Yeshivat Tekoa.