The group surveyed 44,000 people aged 40 to 79 in Miyagi Prefecture from 1995 to 2006, categorizing them into four groups based on body- mass index, or BMI -- skinny at a BMI below 18.5, normal above 18.5 and below 25.0, overweight above 25.0 and below 30.0, and obese above 30.0.

Among those 40 years of age, the average remaining life span is the longest for the overweight category, at 40.5 additional years for men and 47.0 for women, according to the study.

That for the normal category comes the next, at 38.7 additional years for men and 46.3 for women, followed by the obese group at 37.9 additional years for men and 44.9 for women.

According to the study, those categorized as slim have the shortest life expectancy, at 33.8 additional years for men and 41.1 for women.

BMI is calculated by dividing weight (in kilograms) by square height (in meters).

"Those who are too slim are reportedly said to be at higher risk of cardiovascular disease and are more likely to develop pneumonia as nutritional deficiency lowers their resistive force," said Masato Nagai, a graduate student involved in the research.