MedWire News: Oral contraceptive (OC) use causes an increase in basal metabolic rate, leading to a decrease in body weight and percent body fat, show the results of a study in primates.
Contrary to the common belief that OC use causes weight gain, US researchers report that while reproductive-age rhesus monkeys with a normal body mass index (BMI: 22.5-27.3 kg/m2; n = 5) lost a small amount of weight during an 8-month course of OCs, obese monkeys (BMI: 32.5-35.0 kg/m2; n = 5) lost significant weight.
"This study suggests that worries about weight gain with pill use appear to be based more on fiction than on fact," said senior study author Judy Cameron (Oregon National Primate Research Center, Beaverton, USA).
The monkeys took continuous OCs, equivalent to a human dose, and their body weight, percent body fat, and metabolism were measured after 8 months.
Obese monkeys showed a significant 8.58 percent decrease in body weight, while the normal BMI group had a non-significant 0.73 percent decrease.
Percent body fat also decreased significantly in the obese monkeys with OC use, from 32.17 to 20.04 percent, and nonsignificantly in normal weight monkeys, from 13.42 to 11.64 percent.
Importantly, both weight groups had a significant increase in basal (night) metabolic rate that returned to baseline after the study period, which the researchers attribute to the estrogen content of the OC.
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