Red heart dragon fruit is beet red pigment.
Anthocyanins are an important class of pigments in plants, and the color of most plants is also influenced by anthocyanins, like the blueberries and grapes we often eat. Because they are easily oxidized, their ingestion does not usually result in a discoloration of the urine.
But red dragon fruit contains pigment is not anthocyanin, but beet red pigment, this pigment in the body after the digestive system is generally hydrolyzed, and the main chromogenic groups are more stable, especially beet aldolines are not easy to be degraded by the human body, so it will be discharged through the urine, stool and sweat glands.
And urine is the body cycle of the "scavenger", which is composed of 95% of water plus 5% of the metabolites, the 5% of the metabolites if there is a natural pigment of the fruit, there may be color; and sweat glands contain pigment trace, people are generally very difficult to detect.
Expanded:
Red Dragon Fruit contains a natural pigment called "beetrootin". The beetroot red pigment is not easily absorbed and will be excreted in the urine and stools. When this happens, you don't have to be nervous, drink more water and relieve yourself a few times, the color of your urine will return to normal.
Beet pigment is a natural pigment, safe and non-toxic, can be used for food coloring. China's health standards for the use of food additives (GB2760-81) approved beet red pigment can be used as food coloring, and provides that "can be used in various types of food, according to the production needs of the appropriate amount of use".
People's Daily Online - Why eat red dragon fruit will "urine blood"?