@ariella (C) is completely irrelevant because this is not about whether everyone who eats foods prepared with N5 pays attention to their caloric intake.
The flaw here is that while eating foods with N5 may not result in consuming fewer calories, it may still result in lowering fat intake, so it is incorrect to state that "studies indicate that N5 is of no use to such people."
Remember, "such people" here is referring to "people who need to reduce their intake of fat AND to consume fewer calories."
Hope that helps! Please let us know if you have any other questions.
