Kardashian, who is expecting her first child with boyfriend Kanye West, has been the subject of intense scrutiny recently and even felt compelled to defend her choice of maternity wear.
However, Paltrow stood up for the reality star at the launch of celebrity trainer Tracy Anderson's new workout studio.
"I think that women should support each other, especially through pregnancy," she told Entertainment Tonight. "It's a difficult time and, you know, I think Kim Kardashian looks absolutely beautiful."
She added: "We're supposed to gain weight when we're pregnant! That's how God intended it!"
Anderson, who has been working with Kardashian throughout her pregnancy, revealed that she has been urging the reality star to relax and not worry too much about her weight.
"I think that [the comments about her pregnancy are] ridiculous," she said. "I think it's horrible. It just is sad for us as human beings - who does that?"
Kardashian's sister Khloe Kardashian has described the weight jibes as "disgusting", while Jenna Dewan-Tatum - currently expecting her first child with husband Channing Tatum - recently urged her Twitter followers to be kind to pregnant women.
Watch Gwyneth Paltrow, Tracy Anderson and Molly Sims discussing Kim Kardashian's pregnancy below: