People who need to reduce their intake of fat and to consume fewer calories often turn to fat substitutes, especially those with zero calories such as N5. But studies indicate that N5 is of no use to such people. Subjects who ate foods prepared with N5 almost invariably reported feeling hungrier afterwards than after eating foods prepared with real fat and consequently they ate more, quickly making up for the calories initially saved by using N5. The reasoning in the argument is most vulnerable to criticism on the grounds that the argument fails to consider the possibility that ['the total fat intake of people who eat foods prepared with N5 tends to decrease even if their caloric intake does not', 'N5 has mild but unpleasant side effects', 'many foods cannot be prepared with N5', 'people who know N5 contains zero calories tend to eat more foods prepared with N5 than do people who are unaware that N5 is calorie-free']