Ashlee Simpson-Wentz has hit out at critics of her sister Jessica's fluctuating weight.

The singer came under fire in January when she was pictured performing with a new fuller figure at a concert in Florida.

However, in an interview with Women's Health, Ashlee said her sister had “an incredible body” and blasted those who thought otherwise.

“I feel sorry for anyone who would judge her, because she's one sexy lady," she said.

"It's disgusting that people would say those things."

Meanwhile, Jessica proved she was getting back in shape last week when she posted a picture of herself on Twitter wearing ice packs over her knees.

In a separate message, she revealed that she had been working with her personal trainer Mike Alexander.

“He has trained me so much thru (sic) the years. Dukes Of Hazzard!!” Jessica wrote.

Jessica Simpson - Weight Watch