PARIS, Feb 17 (Reuters) - U.S. investment firm Artisan Partners on Wednesday called on French food group Danone to separate its medical nutrition business from its baby foods unit and offload its Asian water brand Mizone to boost returns.

Danone, touted as a prime target for an activist fund, has come under pressure in recent weeks to make management changes as some investors criticised weak returns at the food group and demanded it split the roles of chief executive and chairman.

Shares in Danone, whose revenue and margins have lagged those of rivals such as Nestle, lost nearly 30% last year. They were up 1.53% at 1348 GMT.

"Medical nutrition must be separated from baby nutrition, two businesses that have nothing to do with each other," Jan Bennink, an adviser for Artisan Partners, which has built a 3% stake in Danone and criticised the group's strategy, told Le Figaro newspaper.

Bennink once ran Danone’s fresh food products business and other consumer goods groups including Dutch baby food producer Royal Numico.

"Asian brand Mizone would be better managed by another owner", he said, adding that Danone's bottled water brands Evian, Badoit and Volvic were priorities for the company.

He said he had met Danone's board members Michel Landel and Gilles Schnepp, adding: "The meeting went very well."

The meeting took place ahead of Danone's 2020 results on Feb. 19. Danone declined to comment.

Last week, Artisan Partners joined activist investor Bluebell Capital Partners in criticising Danone's strategy and performance. It notably demanded Danone split the roles of chief executive and chairman and said Danone had not invested enough in innovations and areas such as marketing to support its products.

Last month, Bluebell Capital Partners, whose executives have pushed for changes at fashion label Hugo Boss in Germany and lender Mediobanca in Italy, called on Danone chairman and chief executive Emmanuel Faber to step down.

Faber has been Danone chief executive since 2014 and took on the chairman's role as well three years later.

Government spokesman Gabriel Attal said on Wednesday he would not comment on criticism of Danone by its shareholders as the food group is a private company.

Last month, however, a deal worth close to $20 billion between Carrefour, also a French private company, and Canada's Couche-Tard, was killed off by French ministers who said the food sector was of strategic national importance.

(Reporting by Sudip Kar-Gupta and Matthieu Protard, Dominique Vidalon; Editing by Edmund Blair and Emelia Sithole-Matarise)