Following the almanac calendar based on the cycle of the moon, many Buddhists and Taoists worldwide observe a vegetarian diet on the 1st and 15th day of each lunar month, as well as the different Buddhas’ birthdays. Some will choose to take on a full day of vegetarian diet or simply half a day (11 pm the day before to 11 am day itself), depending on what works best for them in their circumstance. For Buddhist, these are the Uposotha days (recitation of sutras or chanting, and repentance) and for the Taoists, it is believed that these days are auspicious to perform certain tasks like new business opening, house moving, ceremonies, general praying. Hence the abstinence from meat and various stimulants is good for them to avoid bad karma, accumulate good merits and blessings.
Point to note: The Buddha did not dictate that a Buddhist must not eat meat. Buddhism advocates vegetarianism with the intention to cultivate peace, kindness, and simplicity in the hearts of people who wish to learn from Buddha.
Whichever your motivation or intention, it is certainly a good break on your diet to add more vegetables and quality carbs in the routine!