Being obese may takes years off your life and also subject you to chronic diseases linked to being overweight that can lower the quality of your life, researchers are reporting.

Those diseases, including diabetes and heart disease, may cost people an average of eight years of life and rob them of two decades of what might otherwise be a healthy life, researchers at McGill University in Canada say.

When in your lifetime you put on that extra weight is a key factor in that and the worst outcome is seen in people who gained those pounds younger in life, says epidemiologist and study author Steven Grover.

"Not only is excess body weight associated with a significant reduction in life expectancy, but with an even greater reduction in healthy life years," he says.

For the study Grover and research colleagues analyzed data on 4,000 people who took part in the National Health and Nutrition Examination Survey conducted by the U.S. Centers for Disease Control and Prevention.

Using survey data from 2003 to 2010, they created a computer model capable of estimating the risk of developing heart disease and diabetes in adults of different body weights.

Looking at the effect excess weight had on years of life lost and also healthy years lost, the researchers found very obese people could lose up to eight years of life, while obese people might lose up to six years.

Even people classified as merely overweight could lose up to three years of life, the researchers reported.

"The pattern is clear -- the more an individual weighs and the younger their age, the greater the effect on their health," Grover says. "In terms of life-expectancy, we feel being overweight is as bad as cigarette smoking."

Losing that weight through diet and exercise is difficult for many people, Grover acknowledges, but potential benefits of doing so are significant, he says.

For example, he says, losing just 10 pounds or committing to some physical activity for as little as a half hour a day has been shown to lower the risk of developing diabetes by 60 percent.

"The potential benefits of losing weight and exercising in preventing a heart attack or stroke are also substantial," he says.

The McGill researchers say they've embarked on a 3-year study involving local pharmacies across Canada to determine if providing patients with weight-loss information and offering a web-based health program could help them adopt better lifestyles, including healthier diets and more regular physical activity.