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Introduction: The short-term and longterm effects of heated soy oil on bone metabolism in ovariectomised Sprague-Dawley rats were studied.

Methods: Three-month-old female rats, were divided into five groups: normal control (NC); ovariectomised control (OVXC); ovariectomised and fed rat chow with added fresh soybean oil (SOF) or once-heated soy oil (SO1) or five-times-heated soy oil (SO5). Short-term parameters measured after one month were serum interleukin-6 (IL-6) and osteocalcin. Long-term parameters measured after six months were the structural bone histomorphometrical parameters. Vitamin E content in the soy oil subjected to the different heating treatments were also measured.

Results: Rats in the SO5 group had higher levels of IL-6 after one month compared to the other four groups. Osteocalcin levels in the SO1 and SO5 groups remained high after treatment, while those in the NC and SOF groups declined. After six months, bone mass declined in the SO5 group. Vitamin E assay in the oils showed that levels of alphatocopherol decreased after heating the oil once and five times, while levels of gammaand delta-tocopherols only declined after heating five times.

Conclusion: Repeated heating of soy oil destroyed the tocopherols causing raised serum IL-6 and osteocalcin levels, leading to increased bone resorption and osteoporosis in the long term.