Our food itself gets transformed into our thoughts. The sattvic, rajasic and tamasic food create the sattva, rajo and tamo gunas (attributes) respectively. Hence, we have to be very careful with respect to food.
While describing about food, Bhishma mentioned to Dharmaraja that non-vegetarian food must be shunned because it involves violence. Then Dharmaraja said “Ahimsa paramo dharmaha” – Ahimsa (Non-violence) is the greatest dharma. He further asked Bhishma to preach him about the principle behind non-violence. Bhishma went on describing. The footprints of the smaller animals gets merged with that of a larger foot print of an elephant. Similarly, crores of rules of righteousness are merging into non-violence. Hence, Ahimsa is said to be the king of Dharma. It can be compared to that of a cow. So, Dharma has four legs. Even if one leg becomes crooked, dharma in the world will degenerate.
The violence done through mind, mouth, body and consuming flesh are the brutal sins. Because of these four acts, the four legs of the cow called Dharma will be affected. Hence, our elders say that it is wrong to eat flesh. Only if one gives up the above four qualities, it can be considered non-violent dharma. However, those who are used to the taste of flesh cannot give up the habit so easily. Our sages have told us that giving up the habit of eating flesh is a satkarma (good karma) that surpasses even Ashwamedha yaga. The scriptures of dharma say that those who eat flesh will become prey to that flesh again. But, those who eat flesh and even after tasting it, if they give up, then they are considered equal to demi-gods. They are called as demi-gods. They will get the blessings of all the beings and also the king of all beings (Shiva). Those who cannot give it up completely must do so gradually in stages. If one can shun the habit of eating non-vegetarian food in the months (as per lunar calendar) of Ashada, Karthika, Magha and Vishaka, then gradually one can get rid of the habit.
With sattvic food, one can develop the sattvic attributes and thereafter get the darshan of God. This was the teaching of Bhishma to Dharmaraja. By eating flesh, the demonic attributes and tamo guna shoot up giving way to desires and anger which land us in mistakes. How did mahatmas and noble souls win over the desires? There are many who survive only on butter milk and coconut water. Let us consider an elephant. Does it consume any flesh? But, it is extremely strong. It only eats leaves and grass. Now, let us consider tiger. It eats flesh and at the same time, it perishes early. The elephant lives for years together. It survives despite not finding any food. But the tiger will become lean if it does not find food for 10 days. Hence, you need not psychologically worry that you will die out of starvation by not eating flesh and eggs. All nutrients are found even in sattvic food.