The AARP New American Diet plan emphasizes healthy, whole foods over unhealthy, processed ones. — Adam Voorhes

En español | Anna is 55, a mother of three, and a new patient of mine who has struggled with her weight for the past 30 years. She's tried just about every imaginable diet — high carb, low carb, high protein, low fat. She may lose a few pounds, but then she resumes her old eating patterns and the weight returns, often with an extra pound or two thrown in.

Sound familiar? About 70 percent of the over-50 population in America is overweight, with about a third classified as obese. Health complications from obesity cost the United States $190 billion in medical expenses each year. Obesity also shortens lives: An Oxford University study found that an obese person's life span is three to 10 years shorter than that of someone of average weight, about the same loss of life associated with smoking.

So why don't Anna and her fellow overweight Americans just resolve to lose weight? As we all know, it's a little more complicated than that. And fair or not, it gets even more difficult after age 50, because of a slowing metabolism, a loss in muscle mass and a decline in hormones, all of which cause your body to store and retain fat more easily.

So what's a midlife dieter to do? That's where the AARP New American Diet comes in. Seventeen years ago, AARP teamed up with the National Institutes of Health (NIH) to study the effects of dietary and lifestyle choices on the incidence of cancer and other diseases among half a million people ages 50 or older.

Over the past few years the study has provided a wealth of information about what we should and should not eat to live a long, healthy life. In short, we know how certain foods affect our bodies, so we can adjust our diet accordingly to stay healthy and lose weight.

Charlie is fairly typical of my patients: He doesn't always make the connection between what he eats and his overall health. On a recent visit we reviewed his diabetes medications, and I said we could take him off the drugs if he lost some weight. His response: "Dr. Whyte, I've been overweight for 20 years, and I've only had diabetes for two years. You're the first person to tell me my diabetes is related to my weight."

Well, I've got news for you. More than 80 percent of all cases of type 2 diabetes are related to weight. One out of every three cancer deaths is linked to excess body weight, poor nutrition or physical inactivity. Moreover, your risk of dying prematurely increases even if you're just 10 pounds overweight.

Anna and Charlie both needed to lose substantial amounts of weight, but rather than put them on a strict eating regimen, I invited them to try the AARP New American Diet. Instead of focusing on calorie counting or eliminating one food group or another, this plan emphasizes healthy, whole foods over unhealthy, processed ones.

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