'Famine survival gene' offers clues to key cause of obesity
A "thrifty" gene that helped humans survive famine in the stone age may be a key cause of obesity today, research claims.
The CRTC3 gene slows the rate at which fat is burned in the body to conserve energy.
During our hunter-gatherer past, individuals with active versions of the gene would have been more likely to survive long periods without food, scientists believe.
But the same gene became a liability in a world where abundant quantities of rich food were available.
Evidence of CRTC3's role in metabolism has come from US studies of mice lacking the gene that were fed different diets.
Mice with the gene "knocked out" remained as slim as "normal" mice when fed a moderate fat diet.
But when fed the equivalent of a high-calorie diet of steak and cheese, only the normal mice with active CRTC3 genes became obese.
"The CRTC3 knockout mice were leaner and protected from obesity," said lead researcher Dr Marc Montminy, from the Salk Institute in La Jolla, California.
Mice lacking the gene also had twice as many brown fat cells as normal mice.
Unlike "white" fat, "brown" fat is a healthy form of tissue which burns calories to generate heat. Research suggests that people who find it easy to stay slim have more brown fat cells than individuals prone to weight gain.
"Ideas about obesity are based on concepts of feast or famine," said Dr Montminy, whose findings appeared yesterday in the journal 'Nature'.
"As humans, we developed ways of coping with famine by expressing genes like CRTC3 to slow the rate of fat burning. Individuals with these active thrifty genes had an advantage: they could survive long periods without food."