How were slaves fed?

In Colonial America and the United States, slaves were fed as their masters saw fit.

Some masters treated their slaves like one would treat any expensive property (for they were quite expensive for the times): with great care. They fed them well and treated them well so that they would not lose their investment.

Other masters treated the slaves like they were nothing -- they gave them little, perhaps spoiled, food.

[On a side note, Colonial America and the United States are not the only time and place slaves were held. Slaves have been held since the beginning of time -- by Ancient Romans, Ancient Greeks, Ancient Egyptians, African Tribes, the list goes on. I assumed your question was referring to the Americas because they are the most talked about.]