Which outpatient service provides nutritional support through intravenous fluids?

Parenteral nutrition is the correct choice as it involves providing nutritional support directly into the bloodstream through intravenous (IV) fluids. This method is utilized when a patient's digestive system is unable to absorb or utilize nutrients effectively, requiring alternative means to deliver necessary calories, vitamins, and minerals.

In contrast, enteral nutrition refers to the delivery of nutrients directly into the gastrointestinal tract, typically through feeding tubes, which would not be administered intravenously as parenteral nutrition is. Dietary counseling involves guiding patients on food choices and nutrition management rather than providing direct nutritional support, while nutritional assessment is the process of evaluating dietary intake and nutritional status without delivering nutrients. Thus, parenteral nutrition stands out as the option that specifically entails IV nutrient support.