Only vegetarian food is served in the Guruduwara so that people of all religions can partake of it.
Many Sikh leaders opposed to the extremist Hindus who want to eliminate the Sikh identity have suggested serving beef in the Langar to distance Sikhism from Hinduism.
I have a very good friend Amanpreet and he loves a juicy beef steak.
Eating meat is not against the Sikh religion, infact Hindus who advocate vegetarianism are called “fools” in the Sikh Granth:
"The fools argue about flesh and meat, but they know nothing about meditation and spiritual wisdom.
What is called meat, and what is called green vegetables? What leads to sin?
It was the habit of the gods to kill the rhinoceros, and make a feast of the burnt offering.
Those who renounce meat, and hold their noses when sitting near it, devour men at night.
They practice hypocrisy, and make a show before other people, but they do not understand anything about meditation or spiritual wisdom.
O Nanak, what can be said to the blind people? They cannot answer, or even understand what is said.
They alone are blind, who act blindly. They have no eyes in their hearts.
They are produced from the blood of their mothers and fathers, but they do not eat fish or meat."