What is the crucial distinction between 'fat' as a physical component and 'fattening' as an effect?

Fat is a physical component of food; fattening describes the effect on energy balance

The essential difference lies in classification: 'Fat' refers to a specific, required physical component or nutrient category found within foods, chemically defined by its structure of fatty acids linked to glycerol. In contrast, 'fattening' is purely a descriptive adjective concerning the functional impact of that food on an individual's physiological state. It describes the tendency of a food item, based on its overall caloric density, preparation method, and palatability, to encourage an energy surplus over time. This surplus is what leads to the storage of excess energy as body fat, illustrating that the descriptor addresses the *effect* (potential weight gain) rather than the *composition* (the presence of the lipid molecule).