Dieters hoping for a slew of new products with the sugar substitute Splenda may be disappointed next year.

That’s because the maker of sucralose, the key ingredient behind the increasingly ubiquitous no-calorie sweetener, is having trouble keeping up with demand.

The world’s only manufacturer of sucralose, Tate & Lyle PLC, said interest had so outpaced expectations the company won’t take on new U.S. customers until it has doubled production at its plant in McIntosh, Ala., sometime in early 2006.

The company also plans to open a second plant in Singapore, according to a written statement.

Buoyed by a surge in anti-sugar diets such as Atkins and South Beach, Splenda has enjoyed sweet success since its introduction in 2000, appearing in everything from soda and ice cream to candy and jams.

Splenda, which won fans with its sugar-like sweetness and stability in baking, now dominates the $337 million U.S. retail market for sugar substitutes, beating out aspartame sweetener Equal, made by Chicago-based Merisant Corp.

“Sucralose has one of those problems that’s both good and bad to have,” said John Sicher, editor of Beverage Digest. “The demand is tremendous. The supply is constrained.”

Splenda is sold to consumers as a table and baking sugar substitute by McNeil Nutritionals, a Pennsylvania-based unit of Johnson & Johnson. Consumer sales won’t be affected by the tight supply, a company spokeswoman said.

Sales of sucralose to manufacturers as an ingredient for use in other products are handled directly by Tate & Lyle, which is based in London.

How many new sucralose-sweetened products will come to market is difficult to tell, Sicher said.

It depends largely on how many products already have been developed and how much sucralose companies bought in advance.

He said it was too soon to tell how the tight supply might affect existing sucralose-based products at large companies, such as Coca-Cola Co.’s low-calorie “C2” cola, but Tate & Lyle said the Alabama plant would meet the needs of existing customers.