Meat is an essential source of protein. Humans have flat and sharpened teeth suitable and prepared for chewing and grinding meat. Allah has granted man teeth suitable for eating plants and animals, and has created his digestive system in a way that suits digestion of plant food and animal food, which is an evidence on the lawfulness of eating meat.
Allah Almighty said:
{...Lawful to you are all grazing livestock...} [266] Surat al-Mā’idah: 1.
The Noble Qur’an laid down some rules concerning the food:
{Say [O Prophet], “I do not find in what has been revealed to me anything forbidden to eat except carrion, running blood or the swine flesh – which is impure – or a sinful offering in the name of other than Allah. However, if someone is compelled by necessity – neither driven by desire nor transgressing due limit – then your Lord is All-Forgiving, Most Merciful.”} [267] Surat al-An‘ām: 145.
{Forbidden to you are carrion, blood, the flesh of swine, and that which is sacrificed to other than Allah; and that which is killed by strangling, or by a violent blow, or by a headlong fall, or by being gored; and that which is partly eaten by a predator unless you slaughter it [before it dies]; and that which is sacrificed to idols. Also it is forbidden to use arrows [of chance] to determine your decisions. This is all evil practice.} [268] Surat al-Mā’idah: 3.
Allah Almighty also said:
{Eat and drink, but do not waste, for He does not like the wasteful.} [269] Surat al-A‘rāf: 31.
Ibn al-Qayyim (may Allah have mercy upon him) said: "He instructed His slaves to consume what maintains their body from food and drink, which must be according to what benefits the body in terms of quantity and quality. Once it exceeds this, it becomes wastefulness. Both are unhealthy and cause diseases: refraining from food and drink or consuming them wastefully. So, the ultimate way of maintaining good health lies in these two words." "Zād al-Ma‘ād" (4/213).
Allah Almighty described Prophet Muhammad (may Allah's peace and blessings be upon him) saying: {...He makes lawful for them what is pure and makes unlawful for them what is impure...} [271] Allah Almighty also said: {They ask you [O Prophet] what is lawful to them. Say, “All good things are lawful for you...} [272] Surat al-A‘rāf: 157. Surat al-Mā’idah: 4.
Thus, all pure things are lawful and all impure things are unlawful.
The Prophet (may Allah's peace and blessings be upon him) clarified how the believer should act regarding his food and drink, as he said: "The son of Adam does not fill any vessel worse than his stomach. It is enough for the son of Adam to eat a few mouthfuls to straighten his back, but if he must (fill his stomach), then one third for his food, one third for his drink, and one third for his breath." [273] Narrated by At-Tirmidhi.
The Prophet (may Allah's peace and blessings be upon him) also said: "There should be neither harm nor reciprocal harm." [274] Narrated by Ibn Mājah.
The Islamic manner of slaughter, namely cutting the animal's throat and esophagus with a sharp knife, is much more merciful than the electric shock and strangulation that cause the animal to suffer. Once the blood stops flowing to the brain, the animal feels no pain. As for the shaking of the animal at the time of its slaughter, it is not caused by pain; rather, it is caused by the rapid blood flow that facilitates the process of getting all the blood out unlike other methods that block the blood inside the animal body causing harm to those who eat its meat.
The Prophet (may Allah's peace and blessings be upon him) said: "Verily, Allah has enjoined kindness for all things; so when you kill, kill with kindness; and when you slaughter, slaughter with kindness. Let one of you sharpen his blade and spare suffering to the animal he slaughters." [275] Narrated by Muslim.