Why women pile on the pounds as they age – and it may not be their fault
An enzyme involved in fat production is suppressed by the female hormone oestrogen, say U.S. researchers
But this is lost after menopause, causing weight gain
15:55 GMT, 4 January 2013
16:06 GMT, 4 January 2013
An enzyme which protects against fat production is lost after the menopause, causing women to gain weight
It's one of the most frustrating things about getting older – piling on the pounds, no matter how hard you try to keep them off.
Now scientists have discovered one reason – for women, at least.
After the menopause, the activity of a particular enzyme involved in fat production increases.
Known as Aldh1a1, it causes us to store a dangerous type of fat around the internal organs, known as visceral fat.
This is strongly linked with type 2 diabetes, heart disease and cancer and is produced by an enzyme triggered more in females when both sexes eat a high fat diet.
Researchers at the University of Ohio found that the female hormone oestrogen suppresses the effects of the enzyme. The downside is that once levels fall after the menopause, it is free to work its magic – hence the weight gain.
By targeting Aldh1a1, researchers may be able to develop an obesity treatment specifically for women, said study researcher Ouliana Ziouzenkova, an assistant professor of human nutrition at Ohio State University.
The researchers surgically removed the ovaries of mice to test whether oestrogen could be related to visceral fat production in females. As soon as the animals became menopausal and weren't producing estrogen, they began to produce retinoic acid, which led to visceral fat formation.
'Oestrogen was sufficient to protect female mice from both hormonal and, partially, diet-induced obesity,' said Dr Ziouzenkova.
'This means oestrogen is suppressing
activation of the obesity-inducing hormone, and as soon as we lose this
[it] during menopause, the
visceral fat starts to grow,'
The study is published in the January issue of the journal Diabetes.
The researchers also found that women
are more likely to develop a 'muffin top' than men are to get a pot
belly because of the different way the enzyme works in the body.
The enzyme, known as Aldh1a1, it causes us to store a dangerous type of fat around the internal organs, known as visceral fat
Female mice who ate a high-fat diet had more Aldh1a1 activity and stored more fat around the abdomen than male mice who ate a high-fat diet.
When researchers genetically altered mice to lack the enzyme, females stayed lean especially in the abdominal area even when they ate a lot of fat. Males also developed less fat, but the effect was far less significant.
The results suggest the enzyme, which produces a powerful hormone that drives up visceral fat cells, could be a target for anti obesity therapy in women.
Dr Ziouzenkova added: 'If you asked most people what they believe causes obesity, they would probably say high food consumption and a sedentary lifestyle.
'But we see there are genetic factors telling the body what to do with fat. A high fat diet acts on our genetics to make us more fat or less fat. The diet is not powerful enough to do this on its own.'
Further experiments found female mice lacking the enzyme burned the fat away, by using it to heat up their bodies.
Researchers also studied fat from human surgery patients and found the same enzyme was present in tissue.