By Bhanvi Satija

June 20 (Reuters) - Treatments designed to help patients preserve muscle while losing weight with popular obesity drugs by Eli Lilly LLY.N and Novo Nordisk NOVOb.CO could generate more than $30 billion in sales by 2035, analysts at TD Cowen said on Friday.

About a dozen companies are racing to develop such therapies, most of which are being tested in combination with Lilly's Zepbound or Novo's Wegovy, both of which target the GLP-1 protein to help control appetite.

The initial Wall Street estimates for muscle-preserving therapies follow promising mid-stage results from experimental drugs developed by Regeneron REGN.O and Scholar Rock SRRK.O.

Investors are closely watching mid-stage data from Lilly's muscle mass-preserving drug, bimagrumab, which is scheduled for presentation at a medical conference next week.

Analysts have projected that obesity drugs sales could reach $150 billion a year by the early 2030s. The unmet need to preserve muscle will grow with the use of GLP-1 drugs for obesity, said TD Cowen analyst Tyler Van Buren.

Doctors have raised concerns that patients may experience a decrease in overall strength due to muscle loss associated with Zepbound and Wegovy, while experts suggest that more muscle can help patients maintain long-term weight loss.

Van Buren said that the first such treatment could launch by 2028, although regulatory challenges remain because these treatments must demonstrate additional health benefits to secure approval.

"We believe quality of weight loss and lean mass preservation ... is far too important for long-term health outcomes to be ignored and that this will be figured out," Van Buren said.

Some of the new drugs target the myostatin protein, which is associated with muscle growth, and are expected to see broader use due to their superior safety profile, capturing the majority of the market share, Van Buren said.

Other drugs target activin, a protein with multiple biological functions. Van Buren said that activin-based drugs will be reserved for patients at higher risk of losing strength, forecasting sales of about $5 billion by 2035.

(Reporting by Bhanvi Satija in Bengaluru; Editing by Mohammed Safi Shamsi)

((Bhanvi.Satija@thomsonreuters.com; Outside U.S. +91 9873062788;))