“You have to work extremely hard, sometimes more than you want to,” says Garner, a mother of two from Grove City, Ohio. “As opposed to your husband, who stops eating two cheeseburgers a week and suddenly loses 10 pounds.”
It’s not just Tammy’s imagination. For generations women have lamented how easily they gain weight as they get older, especially around the midsection, and how difficult it is to lose it, compared to men.
Now, scientists may know one of the reasons why.
Researchers at Ohio State’s Comprehensive Cancer Center have found that a high-fat diet triggers a chemical reaction involving a particular enzyme in female mice, that may lead to weight gain in the abdomen.¹
Humans share the same enzyme, which could not only help explain how women gain weight, but could shed some light on why they tend to store more fat following menopause.
“In females - but only in females - this process leads to the production of a hormone, which was associated with the development of obesity,” said Ouliana Ziouzenkova, assistant professor of human nutrition at Ohio State University and senior author of the study. “Somehow, in males, this mechanism was not really working.”
When eating a high-fat diet, this chemical reaction took place more consistently, causing females to develop and store much more visceral fat, or the fat stored in the midsection, around vital organs. It’s this type of fat that becomes particularly dangerous as we age, contributing to diseases like heart disease, high blood pressure and type 2 diabetes.
So, why is it that females may be more prone to this problem than males?
The difference may involve the female hormone estrogen. Younger women have higher levels of estrogen, which appears to help them burn fat more efficiently by suppressing this particular enzyme. But as women get older, estrogen levels drop, and when they do, this enzyme is much more active and more prevalent in females.
“On high fat diets, it could be increased as high as 9-fold,” said Ziouzenkova. “But only in the females, not in the males. This leads to fat formation in females at much higher rates,” she said.
The enzyme in question is known as Aldehyde Dehydrogenase 1, or Aldh 1a1. When it comes to visceral fat formation, it is part of a complex reaction involving not only hormones, but vitamin A as well. But this study shows that this enzyme appears to play a crucial role.
In fact, in mice that were altered to remove the enzyme, females remained lean, even when they ate more food than others. The researchers determined that without Aldh1a1, the females were not producing retinoic acid, and that protected them from producing visceral fat.
“We are really talking about a uniquely female mechanism here,” said Ziouzenkova.. “This may be a first step in developing sex-specific therapy for obesity. But it has to be in a very targeted way.”
Ziouzenkova says deleting the enzyme genetically purely to control fat levels would be damaging, because Aldh1a1 is present in all cells, meaning it has additional functions. So, that’s something scientists will have to take into consideration with any possible therapy involving the enzyme.
The research is published online in the journal Diabetes.¹
¹Autocrine Function of Aldehyde Dehydrogenase 1 as a Determinant of Diet- and Sex-Specific Differences in Visceral Adiposity, Diabetes. Published online August 28, 2012. Online:http://diabetes.diabetesjournals.org/content/early/2012/08/26/db11-1779.abstract?sid=151bfb47-6ae4-41e1-8f59-0188b71dec9e