The Skinny on the Olsens' Starbucks

(Wireimage)

Mary-Kate and Ashley Olsen better get the skinny on their favorite Starbucks beverages soon!

The caffeine addicts always request a Grande nonfat latte from the coffee empire, but a source tells OK! there's way more to what they ordered.

An ex-barista at the twins’ local Starbucks in their West Village, New York neighborhood made sure that skim milk was not on the menu or in the girls' cups when they came in.

“The barista thought the Olsens were too thin, so whenever they ordered their usual drink, he would replace the skim milk with full-fat!” the source reveals.

Sneaky, sneaky!

However, the Olsens’ rep tells OK!, “This is ridiculous.”