The fruit often associated with the saying "an apple a day" is the apple itself. The full saying suggests that consuming an apple daily can contribute to good health, emphasizing the importance of eating fruit and maintaining a balanced diet. Apples are rich in essential nutrients, including fiber and vitamin C, making them a popular choice among health-conscious individuals. The phrase has been adopted into popular culture to promote wholesome eating habits, and although it underscores the value of fruit consumption, it should be noted that a diverse diet is key to overall health.