Final answer:
The nutritionist's claim that humans are biologically adapted to a diet of wild foods is a premise used to support the main conclusion, without explicit justification provided for that premise itself.
Step-by-step explanation:
The claim that humans are still biologically adapted to a diet of wild foods serves as a premise for which no explicit justification is provided, but which is used to support the nutritionist's main argument that a diet consisting of wild foods will result in better health.
As such, the correct role of this claim in the nutritionist's argument is option (B): It is a premise for which no justification is provided, but which is used to support the argument's main conclusion.