It may even be robbing you of part of your life.

"We could predict that it would shorten your life-span, but until recently, nobody could put a number on it. Now, thanks to two studies, we know."

The results, Keith says, paint a scary picture for people who lose control of their waistlines beginning in early adulthood.

One study, conducted by Johns Hopkins University Medical School, compiled data from several U.S. mortality studies over a three-decade period and concluded that obese men in their 20s would lose 13 years of life.

It gets even worse for obese smokers, Keith says.

"Smoking has been shown to cut another seven years from your life-span, which means that if you’re obese and a smoker in your 20s and remain that way for the rest of your life, you could lose about 20 years."

A Dutch study released at about the same time as the Johns Hopkins University study revealed that people who become obese by age 40 lose about seven years of life.

As Keith sees it, the studies are ironic in an age when more and more people are living to 100. Even so, he says, it underscores just how much of life people needlessly forego when they follow bad lifestyle habits.

"While mean life-span is currently about 75 years, the studies show that if you’re obese by age 20, this boils down to a mean life-span of about 61 years. If you’re obese by about age 40, you can expect to live to be about 68.

"This really puts it into stark terms when you consider that people have the potential of living to age 100."

It gets even worse when one considers another lifestyle behavior, physical exercise, a factor that was not explored in the two studies.

"If you look at people who are sedentary, the figures come down even more," he says. "People who are obese, who smoke and don’t exercise have a strong chance of living only into the mid-50s – just a little over half of their potential life-span."

The good news is that people who reverse these bad habits, get active and lose weight can change their future, Keith says. And the sooner they start, the better.

"Several studies have shown that ex-smokers who survive 10 years after they quit smoking live about as long as people who never started smoking," Keith says. "And the same probably holds true for obese people."

"But the longer you wait, the less effective these lifestyle changes are going to be."