History of Brahmin diet
Dietary habits and dietary customs have played a significant role in the formation, evolution and development of the social systems in India. Vegetarianism is an integral component of most schools of Hinduism, although there are a wide variety of practices and beliefs that have changed over time. By one estimate, 30% of all Hindus are ovo-lacto vegetarians. Some surveys including one by the Office of Registrar General and Census Commissioner of India show that 60 to 70% Indians as either ovo-lacto-vegetarians or non-vegetarians. Since Hindus constitute almost 80% of the Indian population  and taking surveys such as these into account, it is probable that a major proportion of Hindus are not vegetarians. None of the Hindu sects have ever been found to enforce vegetarianism. According to the ancient Indian epic Mahabharata, there is a mention of a king named Rantideva who achieved great fame by distributing grain and meat among his subjects. Taittirīya Brāhmaṇa, a commentary on the Yajurveda categorically states: `Verily the domesticated animal as food (atho annam via gauh)'. Later Hindu texts provide unreliable evidence of meat consumption. Manusmriti, another Hindu text does not express any discouragement towards meat  consumption. The ancient text Rig Veda promotes vegetarian diet but does not prohibit meat consumption. According to the Rig Veda (X. 86.14), Indra says that twenty bulls were cooked for him. The Rig Veda (X.91.14) also states 'For Agni were sacrificed horses, bulls, buffaloes, barren oxen and rams'. It appears from the Rig Veda (X.72.6) that domesticated animals back then were slaughtered by a quick painless method involving either a sword or an axe. Dietary habits in Hindu scriptures. From the Vedic ages up to the earlier times when Dharma sutras were composed, the four "varnas" or social classes had  only minor differences in diet and lifestyle. People of all "varnas" had some similarities in food choices but vegetarianism was preferred over meat consumption. Vedas. No strict dietary laws have been mentioned in either of the four Vedas, but Dharma sutras do mention some dietary prescriptions. Animal meat consumption was not forbidden in the Dharma sutras and tsacrificial animals were often consumed as food by tribal popualtions. It was extremely difficult, in fact almost impossible, to have been a vegetarian in Vedic times anywhere in the world. Almost all the fruits and vegetables, so commonly available today, had not been  domesticated to be fit for human consumption while cereals, the only vegetarian food that could be stored to eat at a later time, were very scarce till about 4,000 years ago when they first appeared with the Harappans and then slowly spread to other areas. The Harappans only had barley, millets and a little wheat. Rice only came to India from south East Asia very much later. Tenth mandala of the Rigveda mentions cows being slaughtered in honour of Indra and other deities.It also mentions butcher houses that were erected to slaughter cows.Further Yajurveda mentions Ashvamedha or the  horse sacrifice, and even Purushamedha or the Human sacrifice(Yajurveda (VS 30–31)).The flesh of the sacrificial animals was partaken by the sacrificer.Eating of sacrificial human was later abandoned by the Brahmins,at the cost of logic inconsistency. The custom of animal sacrifice still continued in the remote villages. The earliest Hindu scriptures belong or refer to the Vedic period which lasted till about 500 BCE according to the chronological division by modern historians. In the historical Vedic religion of Hinduism, following references exist for meat consumption. The Rig Veda (10.87.16-19) speaks about the flesh of the cattle and the  horses: In therapeutic section of Charak Samhita (pages 86–87) the flesh of cow is prescribed as a medicine for various diseases. It is also prescribed for making soup. It is emphatically advised as a cure for irregular fever, consumption, and emaciation. The fat of the cow is recommended for debility and rheumatism. Most consider this as a disapproval of the cow slaughter and meat eating in general. Others put it in the context of demons and evil spirits (Yātudhāna) stealing the cattle and the milk. Though alternative translations by Swami Dayananda Saraswati reject such claims and give the 'correct' interpretations  and translations in the light of the Brahmanas and Vedangas. According to Dayananda and Yaska, the author of Nirukta (Vedic Philology), Yātudhāna means Cattle -eaters (Yātu - Cattle / flesh of Cattle + Udhāna - eaters/ consumers). The Atharva Veda bans only the eating of the raw flesh, human flesh and fertilized eggs: The Yajurveda mentions Ashvamedha or the horse sacrifice, and even Purushamedha or the Human sacrifice(Yajurveda (VS 30–31)). The Purushamedha or Human sacrifice was purely ritualistic, and there is no proof of a human ever being sacrificed. Later texts. Several highly authoritative scriptures also bar violence against domestic animals except in  the case of ritual sacrifice. This view is clearly expressed in the Mahabharata (3.199.11-12; 13.115; 13.116.26; 13.148.17), the Bhagavata Purana (11.5.13-14), and the Chandogya Upanishad (8.15.1). For instance, many Hindus point to the Mahabharata's maxim that "Nonviolence is the highest duty and the highest teaching," as advocating a vegetarian diet. It is also reflected in the Manu Smriti (5.27-44), a particularly renowned traditional Hindu law book (Dharmaśāstra). These texts strongly condemn the slaughter of animals and meat eating. Mahabharata there is a mention of a king named Rantideva who achieved great fame by distributing foodgrains and  beef to Brahmins. Taittiriya Brahman categorically tells us: `Verily the cow is food' (atho annam via gauh) and Yajnavalkya's insistence on eating the tender (amsala) flesh of the cow is well known. Even later Brahminical texts provide the evidence for eating beef. Even Manusmriti did not prohibit the consumption of beef. Brahmanas. Aitareya Brahmana of the Rigveda, mentions the rules for distribution of the different parts of the sacrificial animals among the priest. Further it again mentions that a Kshatriya sacrificer is not allowed to eat sacrificial food (sacrificed animals and other food items), but the "Brahma" priest  eats his portion for him. Sutras. Baudhayana says (Baudhayana Dharmasutra), carnivorous animals, tamed birds, pigs, and cocks should not be eaten. Five-toed animals, animals with cloven hoofs, birds that feed scratching with their feet, etc. may be eaten. Apastamba (Apastamba Dharmasutra) gives another list of animals not to be eaten. He also mentioned that during Shraddha, meat should be offered to the ancestors. Brahmins of South India. Some of the south Indian Brahmins during the "sutra" period, like those of North India were meat eaters. "Kapilar"(Puṟanāṉūṟu, poems 113,119), a poet in ancient Tamil Country, says: There is a dispute  as to all early Brahmins of Kerala were vegetarians in those days."Kurumthokai" and "Perumpanattuppatai" give details of vegetarian food and not meat dishes. But the above mentioned poet Kapilar is seen to extol the non- vegetarian dishes and liquors and hailed from part of Tamil country which is now known as state of Kerala. Impact of Buddhism and Jainism. From the early centuries of the Christian era, Buddhism and Jainism contributed much to the crescent belief that nonviolence is supremely valued which stimulated growing hostility to the slaughter of live animals. Due to the sacrifice of cattle, there was  a big famine in most parts of the country. People who were forced by Brahmins to provide them whatever they want, slowly started drifting towards other religions which were by that time following non-violence. Priests who participated in sacrifices and eating the flesh of the animals were degraded. To protect their community and its existence the Brahmins stopped sacrifice and replaced it with coconut. For the same reasons, high proportion of Brahmins gave up partaking flesh and fish. In 4th and 5th century CE. in the Tamil country the cults of Vishnu and Shiva, had to fight against those  of the Jains. The Vaishnava and Shaiva could not make much headway against the Jains (who believed in non-violence and vegetarianism), if they did not give up eating of flesh. Hence they adopted abstention from meat and liquor as one of their fundamental principles. Recent research indicating pre-Śramaṇa origins. While the yogasutras of Patanjali are dated somewhere between 500 BCE and 400 CE, Patanjali was not the founder of the yogic school of philosophy. Rather, Patanjali drew upon the vedantic literature Like the Upanishads and Samkhya philosophy both of which have Vedic roots. The influence of Samkhya on  yogasutras is so great that some scholars preferred not to distinguish yoga as separate from Samkhya, rather presented it as another form of Samkhya. More recent scholarship establishes the origins of Samkhya in the vicinity of 1500 BCE noting its influence on Buddhist and Yoga schools of Indian philosophy. Present. Vegetarian brahminical Hinduism is mostly a Hindi belt phenomenon, even though former PM and UP brahmin Atal Bihari Vajpayee was famously nonvegetarian. Maharashtrian brahmins who founded RSS may be strictly vegetarian but Maharashtra as a whole is almost entirely meat and fish eating. Bengali Brahmin and Kashmiri brahmins are nonvegetarian  as are coastal brahmin castes like the fish eating Saraswats.