Dec. 8, 2005 -- Scarce calories have been linked to increased physical activity in mammals, and genetics may be the reason why.
So says a study in Science.
Humans are mammals, but people weren't studied in this project. Instead, mice were the subjects. The mice's calories were drastically slashed (by 40%) for nine months.
Some of the mice had a gene called Sirt1. They became more active on the low-calorie plan.
Other mice didn't have the Sirt1 gene. They weren't particularly perky when their calories were scarce.
The Sirt1 gene may be "required," write the researchers, for increased physical activity when mammals' calories are restricted.
The researchers included Danica Chen, a postdoctoral associate in the biology department of the Massachusetts Institute of Technology (MIT).
They videotaped the caged mice around the clock to monitor the mice's activity. For comparison, they also studied mice on normal diets with and without the Sirt1 gene. Those mice weren't especially active.
Across the board, the calorie-restricted mice with the Sirt1 gene were the most active mice. They spent more time scurrying, jumping, and hanging from the bars on their cages.
The Sirt1 gene was studied for a simple reason. It resembles another gene linked to longevity in calorie-restricted yeast and fruit flies, write Chen and colleagues.
They don't know exactly how the Sirt1 gene affects physical activity or if that gene affects longevity in calorie-restricted mammals.
Mammals do more foraging for food when calories are restricted, the researchers note. Possibly, the mice were hungry and looking for food.
Still, that wouldn't explain why calorie-restricted mice lacking the Sirt1 gene were less active than those with the gene. Both groups of mice were equally able to move, the researchers note.