Sept 1 (Reuters) - Gilead Sciences Inc said on Wednesday its experimental fixed-dose combination treatment for HIV proved as effective in a late-stage study as the company's widely used Truvada combo pill but with significantly less loss of bone mineral density and kidney function.

The company has already sought U.S. and European marketing approval for the new combo pill nicknamed F/TAF, which is meant to be a safer replacement for Truvada, a cornerstone of HIV treatment that has been associated with slight declines in bone mineral density and kidney function.

"The results of this and other recent trials demonstrate the potential of F/TAF to become a next-generation backbone" of treatment for HIV, the biotechnology company said in a release.

Gilead said it plans to submit detailed data from the study at a scientific conference next year.

Results of the 48-week study reinforce the efficacy as well as kidney and bone safety advantages of the new combination pill, Gilead said.

Gilead shares were up 1.6 percent to $102.88 in morning trading on the Nasdaq, outpacing a 1.3 percent gain for the Nasdaq Biotech Index (.NBI).

The Foster City, California-based company has become one of the world's biggest and fastest-growing biotech companies thanks to its antiviral drugs, including its top-selling Sovaldi and Harvoni treatments for hepatitis C.

(Reporting by Ransdell Pierson in New York; Editing by Jeffrey Benkoe)