Carrot juice

 was an beverage made from carrots enjoyed by Melanie Bush for its healthful properties. She tried to get the Sixth Doctor to regularly consume it to improve his health. She claimed that its main ingredient, carrots, were rich in Vitamin A. The Doctor did not particularly enjoy it and claimed it was having an adverse effect upon him. He said, almost certainly untruthfully, that it was making his ears grow and inducing a limited form of colour blindness. (TV: Terror of the Vervoids, The Ultimate Foe)

Behind the scenes
In the real world, the ability of carrots to improve eyesight has been a long held urban myth, one which played a significant role World War II. In 1940, the British Royal Air Force published a story that claimed fighter pilot (nicknamed "Cats' Eyes") had a steady diet of carrots to thank for his flying prowess at night. This kicked off a three year propaganda campaign by the British government to get people to eat more carrots. The aim was was twofold: to encourage the public to eat more carrots as they were one of the few plentiful foods available during the German blockade, and to hide the fact that the United Kingdom was the first country to successfully employ RADAR, which gave their pilots an edge when flying at night.