BANGKOK, Thailand —  Chuang Chuang the Panda is just too heavy to have sex. Thai authorities have put him on a strict diet as part of a long-running campaign to get him to mate with female partner Lin Hui at the Chiang Mai Zoo in northern Thailand.

"Chuang Chuang is gaining weight too fast and we found Lin Hui is no longer comfortable with having sex with him," said the zoo's chief veterinarian, Kanika Limtrakul, adding that Chuang Chuang weighed 331 pounds while Lin Hui is only 253 pounds.

As a result, zoo authorities are cutting out bamboo shoots in the daily meal for Chuang Chuang and giving the obese bear only bamboo leaves, Kanika said.

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The diet plan is the latest in an unsuccessful and often strange campaign by zoo officials to get the two bears to mate.

They have held a mock wedding, announced plans to separate the two to spark a little romance and even talked of introducing panda porn — videos of other pandas mating — to get the pair in the mood.

Thailand rented Chuang Chuang and Lin Hui from China for $250,000 in October 2003 for 10 years. They are expected to generate millions of dollars in revenues from Thai and foreign tourists.

There are as few as 1,600 giant pandas in the mountain forests of central China, according to the zoo. An additional 120 are in Chinese breeding facilities and zoos, and about 20 live in zoos outside China.

Pandas are threatened by loss of habitat, poaching and a low reproduction rate. Females in the wild normally have a cub once every two to three years.