Kate Middleton is undergoing hypnotherapy to help regain her appetite, a friend says.

The Duchess of Cambridge, carrying her and Prince William's first child, is suffering from hyperemesis gravidarum, a very severe form of morning sickness.

Her friend Jessica Hay has revealed the unusual method the mother-to-be is employing in order to restore a healthy relationship with food.

"[She] still looks at food and feels nauseous," Hay told Australia's New Idea magazine.

"[She has] that feeling you have when you've had food poisoning and your stomach's shrunk... [She's using hypnotherapy] in a bid to help with her appetite."

Hay said the therapy was working and Middleton was snacking on wholesome treats such as avocados, broccoli, oatmeal and smoothies.

"She finds it very hard to eat a full meal and gets full very quickly," her friend continued.

"The hypnotherapy is taking away any negative thoughts connected with food from the morning sickness and replacing them with cravings for healthy, nutritious food."

The pretty royal has been looking well lately, even enjoying a night at an acrobatics show for her birthday earlier this month.

Hay said the support of those close to her had helped Middleton cope with the extreme sickness.

"All in all, she's very happy," she said. "With so much family around her and William, they're starting to enjoy the pregnancy after such a traumatic start."

- Cover Media