What is the reason behind Angelina Jolie's veiny arms?

Angelina Jolie's arms can be visibly seen as veins. What cause these veins?

According to registered dietician Sharon Richter of Manhattan,
"A lot of times these stars are following a very clean diet, with very few processed foods and instead a lot of foods that are very, very low in salt."

"That's why the skin looks almost dehydrated; they have very little salt in their diet."

"Cleanses—you know, lemonade cleanse, all that stuff—and good old-fashioned temporary starvation may also be at fault."

"Sometimes, before a photo shoot, celebrities will even do epsom salt baths, which draw the salt out of the body. Or they may undereat for a few days, eat as little as possible, say, 800 calories, to make a certain weight."

Source