By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) – In a possible explanation of why many women gain weight after menopause, a U.S. researcher said on Wednesday that monkeys whose ovaries are removed eat 67 percent more food and gain 5 percent of body weight in just weeks.
Removing the ovaries induces immediate menopause by cutting off estrogen, the so-called female hormone, said Judy Cameron of Oregon Health & Science University.
Reporting to a meeting of the Society for Neuroscience in New Orleans, Cameron said she may be able to help explain why so many women begin to gain weight as they go through menopause, even though many try not to. “When women go through the menopause … women aged 40 to 60 gain weight. But there are also lifestyle changes,” Cameron said in a telephone interview.
Separating biology from lifestyle in a study is difficult, she said, and researchers have been unable to say definitively why women put on pounds.
Monkeys provide a great model because they have 28-day menstrual cycles like humans and also go through menopause, she said.
Her team removed the ovaries of 19 out of 47 monkeys at Oregon Health & Science University. “Low estrogen in primates clearly results in more food intake,” she said.
“In the first two months, they had a 67 percent increase in food intake. These animals are chubby,” she said.
“Their midriffs get a little bit heavier,” she added. “Additionally, we noted an increase of the hormone leptin, which is produced by fat cells and has been shown to play a role in food intake.”
Estrogen gets into the brain, she noted, and could easily affect appetite.
MONKEYS EATING MOST WEREN’T ALWAYS HEAVIEST
Mysteriously, some of the monkeys were able to eat much more without gaining much more weight, while others gained large amounts of weight. “There was very little correlation between what the animals were eating and how much weight they gained,” she said.
Here was the perfect opportunity to test an idea that dieting women have heard for years — that eating at night puts more weight on than daytime eating.
Like people, the monkeys had different eating habits.
“Some eat only daytime meals, she said. “Some get 60 percent of their calories by snacking at night.”
That made no difference.
“Nighttime eaters were not any more likely to gain weight, she said.
Cameron’s team is testing the metabolisms of the monkeys to see if the lack of estrogen affected that.
The findings can help biologists try to track down what effects estrogen has on appetite and metabolism, but it also may be immediately useful, Cameron said.
“People ask, ‘So what?’” she said. “It offers an excuse, but it also offers knowledge. “You need to be aware that as you go through menopause, there is going to be a growing desire for food.”
Menopausal women can watch what they eat and exercise more, she said.
“Perhaps most importantly, this research pertains to the country’s worsening obesity epidemic, she said. “Currently about 30 percent of Americans are considered obese.”
Cameron said she was certain drug companies were working on safer replacements for hormone replacement therapy and perhaps could reformulate them to battle menopausal weight gain.