Even if perhaps one would develop vitamin deficiencies, etc. if one ate only Spice for a long period, would Spice be something that one could eat which would prevent starvation and provide calories that would allow one to survive a long trek through the desert?
Norma Cenva survived on it exclusively. (Expanded Dune universe).
It is not stated if the spice contained calories, vitamins or anything else normally regarded as necessary for survival of people, but:
Her crews constructed an airtight clearplaz chamber where she would breathe gas form melange, without food and water.
Over time she changed. It's not clear if she could have been said to have survived in any traditional sense however:
While remaining sealed in her spice chamber, her body continued to transform, even to the extent that her body no longer existed and she remained nothing less than a disembodied consciousness in a clearplaz globe. This consciousness came to be known as the Oracle of Infinity.