According to research, the eldest born girl is 40% more likely to be obese, compared to their younger sisters.
In fact, researchers found that firstborn girls have worse health generally than their siblings, with the eldest more likely to develop diabetes and high blood pressure, too.
But how much truth is there in these statistics? We put the research to the test with some famous older sisters.
Zooey and Emily Deschanel
Eldest child Emily Deschanel, 38, (star of hit crime series Bones) could hardly be described as larger than her 35-year-old sister Zooey. With their porcelain skin, piercing blue eyes and petite figures - the girls are spitting images of one another.
The Kardashians
Eldest of the Kardashian clan, Kourtney is actually also one of the smallest of the sisters - coming in at just 5 foot, and with a dress size of a UK 6-8. With the average American woman being a UK size 18, she is far below the national norm, and smaller than some of her curvier sisters.
Katie and Sophie Price
Katie’s younger sister Sophie has been on a healthy kick this year, losing three stone in just seven months. But, despite this, glamourous sister Katie is still the more svelte of the two - coming in at a tiny size 8 despite sporting large assets.
Britney and Jamie Lynn Spears
Despite having two kids, going through a public breakdown and being openly addicted to sugar and sweets, princess of pop Britney has a trim bod. As does younger sister Jamie Lynn Spears, who at ten years her junior is the same dress size of UK 8.
Kelly and Aimee Osbourne
The hidden Osbourne sister is just as slender, if not slimmer, than her younger sister Kelly, 30. Despite actively avoiding the limelight (unlike her more famous siblings), Aimee has lost a considerable amount of weight since her teens - just like younger sis Kelly.
The Middletons
The royal sisters have always been skinny minnies, but older sister Kate slimmed down even further when she took on official duties. However, with both sisters a size 6, Kate looks leaner than her curvaceous sister, who caused a stir with her shapely derriere back at the royal wedding in 2011.
The Delevingnes
The eldest of the stunning trio of Delevingne sisters, Chloe, is far from large, appearing just as teeny as her two model sisters, Poppy and Cara.
Paris and Nicky Hilton
Heiresses Nicky and Paris have almost identical bodies, both being long, lithe and leggy. Far from being the larger of the two, 34-year-old Paris is a UK size 6 these days, tiny for her 5 foot 6 height.
In conclusion, we don't think there's all that much weight to these claims of the eldest sibling being the biggest - but what do you make of the research?
Let us know via Facebook or Twitter (@CloserOnline).