Mannatech Inc.’s sales of dietary supplements have surged in the past three years, but some leading nutrition scientists view the products as having little or no benefit, according to a published report.

Mannatech claims that its supplements contain plant extracts that provide essential sugars to the body. Executives of the Coppell-based company tie their products to glycobiology, the study of how sugar molecules function in biology and medicine.

But some leading scientists in the field say Mannatech’s chief product, called Ambrotose, is ineffective and hasn’t been subjected to clinical trials, the Fort Worth Star-Telegram reported Sunday.

“They literally have a sugar pill,” said Ronald Schnaar, a professor of pharmacology at Johns Hopkins University’s medical school. He said the supplement wouldn’t harm anyone but that some people who take them could be helped by other therapies.

Three Nobel Prize-winning scientists have complained to the New York attorney general that Web sites falsely use their research to validate Mannatech products. The Web sites are operated by Mannatech’s independent sales agents, the newspaper reported.

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