How different would a human-like creature be in order to need only half the calorie consumption that we need?
- The species must be capable of surviving in an Earth-like planet.
- The differences between this species and a human should be a possible result of evolution, rather than handwaving.
- The actual environment they'd live in on the planet is unspecified, but they should be able to travel (even if it's costly or unpleasant).
- Extended periods of sleep are off the table. Members of this species should be able to stay awake as long as a human can, although the actual sleep habits can differ.
The following similarities with an average human must be maintained:
- General structure (similar enough to be mistaken for a human when fully clothed)
- Physical strength
Making those creatures lighter and/or shorter is also on the table as long as it doesn't get in the way of any of the constraints. Any other possible change is on the table.
Edit: Despite the difference in calorie intake, they should be as healthy and as strong as a human being who eats normally.