Eat only what you need

A mouse was having a very bad time. She could find no food at all. She looked here and there, but there was no food, and she grew very thin.

At last the mouse found a basket, full of corn. There was a small hole in the basket, and she crept in. She could just get through the hole.

Then she began to eat the corn. Being very hungry, she ate a great deal, and went on eating and eating. She had grown very fat before she felt that she had had enough.

When the mouse tried to climb out of the basket, she could not. She was too fat to pass through the hole.

"How shall I climb out?" said the mouse. "oh, how shall I climb out?"

Just then a rat came along, and he heard the mouse.

"Mouse," said the rat, "if you want to climb out of the basket, you must wait till you have grown as thin as you were when you went in." 

"Food is considered God, as it is the source of a person’s life, body, mind, and character. Eat only what you need. Do not be greedy and take more than you can eat. Wasting food is a great sin; your surplus can feed another stomach.Even a major part of the food you consume, the gross part, is thrown out as waste matter. A minute amount of the food, which is the subtle part, is assimilated by the body and flows as blood. And a minuscule amount, which is the subtlest part of the food, makes up your mind. Therefore mind is the reflection of the food consumed. When demonic tendencies arise in our minds, know that it is from the food we consume. To receive real nourishment, pay attention to the quality of food that you eat and let it be very pure, clean, sanctified, and Satwik." 

Sathya Sai Baba, 'My Dear Students', Vol 2, Ch 2.