Scientists have found tangible signs that a low-calorie diet could reverse signs of ageing in the body.
Most people in the study reduced their calorie intake
A six-month study showed cutting calories lowered insulin levels and core body temperatures.
The Louisiana State University team said further studies were needed to confirm the findings, in the Journal of the American Medical Association.
A British expert said the research was interesting, but that many other factors affected life expectancy.
It is known that reducing the amount of calories that rodents and other animals take in long-term lengthens their life.
It is thought that restricting calorie-intake affects processes in the body such as metabolism and sensitivity to insulin - as well as the health benefits from losing weight.
Researchers from Louisiana State University studied 48 overweight men and women between March 2002 and August 2004.
All were healthy, but none exercised.
They were either put on an eating plan to maintain their existing weight, given a plan to cut their calorie intake by 25%.
A third group was told to restrict their calorie intake and exercise, and a fourth was put on a very low-calorie diet - 890 kcal a day until their weight had gone down by 15%, - followed by a weight maintenance diet.
After six months, the non-diet group had lost an average of 1% of their weight, the calorie restriction group, 10.4%, those who were on a calorie restricted diet plus exercise, 10% and the very low-calorie diet, 13.9%.
Fasting insulin levels - recorded between meals - were significantly reduced in all the three diet groups.
Low insulin levels is one of the common factors to have been recorded in people who live to over 100.
People on either of the calorie restriction diets had reduced average core body temperature, which has been previously suggested to be an aid to living longer.
Being cooler means the body does not have to expend as much energy.
In addition, there was a reduction in the amount of DNA damage - errors that occur when a cell divides - seen in the three groups.
Dr Leonie Heilbronn, who led the research, said: "Our results indicate that prolonged calorie restriction caused a reversal in two of three previously reported biomarkers of longevity.
But she added: "Longer-term studies are required to determine if these effects are sustained and whether they have an effect on human ageing."
Dr Frankie Phillips, of the British Dietetic Association, said the research was interesting because it gave an insight into how losing weight affected the body.
But she said it did not tell the whole story about how long someone will live.
"Socio-economic factors and the environment can also influence how long you live."
She added: "We also know that being obese can cut up to nine or 10 years off someone's life. So by losing weight, you are effectively increasing your life expectancy by that long."
"This study reinforces the importance of being a healthy weight."
But Dr Phillips said she was concerned that some people in the study were put on extremely low-calorie diets - something she said people should only do for a short period of time and under the supervision of their GP or a dietician.