Onions and Garlic are not eaten in a yogic diet
According to Ayurveda, foods are grouped into three categories – sattvic, rajasic and tamasic – foods in the modes of goodness, passion and ignorance. Onions and garlic, and the other alliaceous plants are classified as rajasic and tamasic, which means that they increase passion and ignorance. Rajasic and tamasic foods are also not used because they are detrimental to meditation and devotions. Garlic and onions are both rajasic and tamasic, and are forbidden to yogis because they root the consciousness more firmly in the body. They stimulate the central nervous system, and can disturb vows of celibacy. Garlic is a natural aphrodisiac. Ayurveda suggests that it is a tonic for loss of sexual power from any cause, sexual debility, impotency from over-indulgence in sex and nervous exhaustion from dissipating sexual habits. It is said to be especially useful to old men of high nervous tension and diminishing sexual power. Onions are harmful to the lungs, garlic to the heart, and spring onions to the kidneys. They induce aggravation, agitation, anxiety and aggression so they are harmful physically, emotionally, mentally and spiritually.
Palandu lasunam sigrum alambum grjanam palam
bhunkte yo vai naro brahman vratam candrayanam caret
(Padma Purana, Brahma Khanda 19.10)
O sages, one who eats garlic, onions, drum stick, turnips, bottle gourd and meat, that person should observe a candrayana fast.
Chandrayana vrata is observed for a whole month. It consists in reducing the amount of food which totals fifteen mouthfuls on Full Moon, by one mouthful daily until New Moon when the fast becomes complete and then increasing it in the same manner from the day after New Moon to Full Moon. Complete abstinence from food is also observed for one, three, six, nine or twelve days according to each person’s capacity and inclination.
Among the most auspicious times for fasting are the days of Full and New Moon as well as the eighth and the twenty-third of each month (counting from the first day after New Moon). New Moon Day (Amavasya) is that day of the lunar month which begins when the last crescent of the Moon becomes invisible at dawn – for which reason it may accurately be called No Moon Day. The night before this, that is, New Moon’s Eve, is the Sacred Night of Shiva (Shiva Ratri) which is also known as The Fourteenth Day of Shiva (Shiva-Chaturdashi) and The Dark Night of Shiva (Shiva Kalaratri). Fasting during the day and night on this auspicious occasion is particularly meritorious, and is observed for the expiation of sins as well as for acquiring religious merit.
“O Sages! on the thirteenth day of the dark half of the month, one meal only shall be taken (by the devotee). But on the fourteenth, complete fast shall be observed. The fourteenth of the dark half is sure to bring about the propitiation of Lord Shiva”. Shiva Purana
And by the way, Lord Shiva is the lord of yoga…
vrntakam jalisakam kusumbha smantakam tatha
palandu lasunam suklam niryasan caiva varjayet
gRJjanam kinsukan caiva kukundanca tathaiva ca
udumbaram alavun ca jagdhva patati vai dvijah
One should not eat eggplant, banana leaves, sunflower leaves and asmantaka leaves, onions, garlic. One should not eat sour gruel (a thin watery porridge) or the juice of the tree. One should also give up turnips and beetroots, carrots, kinsuka, forest figs, and white pumpkin. If the twice born persons (twice born mean one that has taken up a spiritual life with proper initiation into it) eat these things, they all become fallen.
palandulasunadini jagddhva candrayanam caret
sraddhe devanpitrnprarcya khadanmamsah na dosabhak
By eating garlic and onion one becomes sinful and as atonement one should perform Candrayana. (Garuda Purana 1.96.72)
Onion, feces-thriving pigs, Selu, garlic, Goplyusa (milk of a cow before the lapse of ten days from calving), Tanduliya (a grain growing in fecal rubbish) and mushrooms— all these are to be avoided. (Skanda Purana 40.9)
The householder taking the rite shall avoid heavy indigestible pulses like Nispava, Masurika etc., stale food, defiled food, brinjals, gourds, cocoa-nuts, garlic, onion, intoxicating beverages and all kinds of meat. (Siva Purana 7.10-12)
He should avoid stalks of lotus, safflower, gold or silver, onion, garlic, sour gruel; so also chatraka (a kind of mushroom), vidvaraha (pork), greasy milk of a cow during the first seven days of calving, vilaya (a particular product of milk) and mushrooms. By eating the small red variety of garlic, blossoms of kimsuka (flame of the forest), so also udumbara (cluster fig), bottle-gourd, a twice-born becomes fallen. (Padma Purana Vol. 42, 4.56.19b -24)
I shall now mention those things that should always be avoided in Sraddha (spiritual rites & ritual). Garlic, onions, globular radish and Karambha (groats or flour mixed with curds), and other articles devoid of smell and with no taste should be avoided in Sraddha. The reason is also mentioned (as follows): Formerly in the fight between devas and asuras, Bali was defeated by suras. From his wounds drops of blood gushed out and from them these articles grew up – hence they are avoided in the Sraddha rite. (Varaha Purana 16.11b-15)
5.5. Garlic, leeks and onions, mushrooms and (all plants), springing from impure (substances), are unfit to be eaten by twice-born men.
5.19. A twice-born man who knowingly eats mushrooms, a village-pig, garlic, a village-cock, onions, or leeks, will become an outcast.