En español | I have two doctors, my left leg and my right leg," wrote British author George Trevelyan in 1913 about the health benefits of walking. Nearly a century later, modern medical experts echo the same advice: Get up and walk.

Walking may be the single best — and easiest — exercise you can do to improve your health in 2012.

See also: Sitting too much may be hazardous to your health.

Not only will going for a daily walk help you feel better now, it will help you maintain your independence and ability to do daily tasks as you age, says Barbara Bushman, a health professor at Missouri State University who has helped older, sedentary men and women start a walking routine.

Research also has shown that walking regularly can help protect the aging brain against memory loss and dementia, help cut the risk of heart disease, and reduce the chance of developing type 2 diabetes in high-risk adults by a whopping 60 percent.

And we're not talking marathon walking either. The peak benefits come from 30 minutes of exercise several times a week, say experts.

Most of us do need to move more: Only 30 percent of people ages 45 to 64 say they engage in regular leisure-time physical activity, and that drops to 25 percent for those 65 to 74, according to the National Institute on Aging, which has launched a "get off your duff" campaign called Go4Life.

Rick Genter before weight loss. — Photo by Jonathan Sprague/Redux

And even if you weigh 400 pounds and can't climb a flight of stairs — you can start walking. Just ask Rick Genter.

Genter, a 51-year-old software engineer in Redwood City, Calif., was morbidly obese 10 years ago. He lived in the Boston area then and spent his whole day sitting at a computer. Walking up a flight of stairs left him gasping for breath.

"My whole family is obese," he says. "My mother died at age 56. My father is at least 150 pounds overweight and on all sorts of medication. I had high cholesterol, high triglycerides and I was convinced I was on my way to diabetes, a heart attack, or both."

Genter joined a medically supervised weight loss program. They told him he needed to do some kind of exercise every day.

"They said, 'Do anything as long as you like it,' " he recalls.

Walking seemed doable, so he started out slowly, walking 30 minutes each day on his lunch break.

"I found I really liked it. And as I started to lose weight, it got easier," Genter says.

As the pounds came off, he began walking to work — seven miles each way — even in winter.

"It felt so great. It made me understand what was meant by 'a runner's high.' "

Nearly a year after he started dieting and walking, Genter had lost 186 pounds and was down to his goal weight of 200 pounds. He got a new job in Northern California, and last year he got married.

Next: Start with small goals and build up your endurance. >>