KIRSTIE ALLEY is on the verge of a “massive breakdown” because a blockbuster lawsuit is threaten­ing to expose her diet program as a pricey scam!

A disgruntled dieter filed the suit on July 20, alleging that Kirstie’s Organic Liaison diet products don’t work and were “nothing more than a healthy deception.” Now, the former “Fat Actress” is terrified that her weight-loss empire is going to come crashing down, according to a source.

“This lawsuit is Kirstie’s worst nightmare because it basically claims she is a fraud,” an insider revealed. “She’s petrified that it’s going to turn her into a pariah among her Hollywood peers.”

In late July, Kirstie was tapped to be a cast member in the all-star season of “Dancing with the Stars,” which premieres on Sept. 24. But now the actress is petrified that her presence on the show is going to bring unwanted attention to the pend­ing allegations. What’s worse, Kirstie is gearing up to promote her new memoir, “The Art of Men (I Prefer Mine Al Dente),” and she fears the book’s November re­lease will be marred by claims that she was cheating her fans “out of money and hope,” said the source.

Kirtsie, 61, who has long struggled with her weight, launched Organic Liaison in February 2010 and later boasted that she had dropped 100 pounds thanks to the products.

But failed dieter Marina Abramyan, who filed the lawsuit against Kirstie’s Florida-based company, claims she bought nearly $200 worth of the prod­ucts and didn’t experience any of the promised benefits.

The lawsuit also charges that Kirstie’s dramatic weight loss came not from the supplements but from an extreme diet and exercise regimen – including the gru­eling five- to seven-hour dance rehearsals for “DWTS.”

Advertisements for Organic Liaison featured Kirstie promising her fans: “I can assure you that if you follow this program, you’ll get healthier, lose weight and not be ‘annoyingly’ hungry.”

One of the supplements, called Rescue Me, retails for $49.95 and is touted on Kirstie’s Organic Liaison website as “the first USDA-certified organic weight-loss product that boosts natural energy.” The ENQUIRER obtained a container of Rescue Me on July 26 at the star’s Organic Liaison store in the Los Feliz area of Los Angeles and asked two top weight-loss experts to evaluate the ingredients.

Dr. Craig Title, who heads a highly regarded weight-loss center in New York City, claims Rescue Me is “sugar, sugar and more sugar.” He added: “It certainly is not a diet drink and won’t promote weight loss.”

And Dr. Gabe Mirkin, a board-certified sports medicine physician from Orlando, Fla., and author of “The Healthy Heart Miracle,” told The ENQUIRER: “I find it incredible that such a high-priced product is allowed to be advertised for weight loss.

“There is no miracle ingredient in this prod­uct that will cause you to lose weight.”

Kirstie claims that she dropped from a high of 230 pounds down to about 140 thanks to her products, but insiders say she was fibbing about both of those numbers.

There was no question that the actress looked phenomenal after her weight loss, but the amazing transformation sparked rumors that she had undergone gastric bypass surgery.

And while she was out promoting her new healthy and active lifestyle, The ENQUIRER reported that Kirstie had started smoking cigarettes again in a desperate attempt to maintain her figure by killing her appetite.

According to the source, Kirstie’s diet lies are now coming back to haunt her.

“Right from the beginning, she was hit with charges that her quick diet fix was too good to be true,” said the source. “And now she’s mortified that she’s once again the laughingstock of Hollywood.”