Lindsay Lohan tries to fatten up pencil thin sister Ali with trip to McDonald's drive-thru

Ali Lohan showcased her pencil thin physique this week as she attended a casting in Beverly Hills.

So it's no surprise to see big sister Lindsay trying to fatten her up with a lunch date at McDonald's.

However, despite dedicating their time to queuing up at the drive-thru window, the girls left with fruit smoothies and not a calorific burger in sight.

Younger sibling Ali, 17, sat in the passenger seat, looking pale and tired as she lifted her sunglasses off her eyes and onto her head.

While she has never carried much excess weight, Lohan Jr. shocked onlookers with her dramatic appearance on Monday, stepping out in skinny jeans and a long-sleeved white top.

There was not an inch to pinch as her waif body looked far frailer than it should for a growing teen.

It is no secret that Ali has been chasing the limelight to follow in LiLo's foosteps, but it seems luck has not been on her side yet.

Despite embarking on a modelling career at the tender age of three, after signing with Ford Model, she is yet to steal the headlines and become a global name.

She flirted with fame with several uncredited appearances in her sister's films, before starring in her own 2008 project Mostly Ghostly: Who Let the Ghosts Out? - which went straight to DVD.

In the same year, Ali raised her profile starring in reality show Living Lohan alongside mother Dina.

Yet her new supermodel heroin chic statistics have secured her a 2012 contract with NEXT models.

Lindsay's weight has also yo-yoed over the years, notably with her shocking weight loss in 2005  when a friendship with Nicole Richie and super skinny stylist Rachel Zoe saw the pounds plummet.

Despite eventually stabilising her weight again, she shrunk further in 2009, with the stress of her tempestuous relationship with then-girlfriend Sam Ronson blamed for her diminishing frame.