I've just come from the stunning 3-D cinema version of Beowulf. In my former life as a Beowulf scholar, I would never have imagined our hero facing a monster with the seductive allure of the seemingly nude Angelina Jolie. However, I was even more surprised by the monster-sized refreshments at the concession stand, especially because I'm not a frequent visitor to the modern megaplex. I saw lone moviegoers struggling with family-sized tubs of butter-drenched popcorn.

The Obesity Society (yes, there is one) estimates that more than 64% of U.S. adults are either overweight or obese. Surveys from the National Center for Health Statistics show that among adults ages 20 to 74, clinically defined obesity has more than doubled in a single generation, from 15% in the mid-1970s to contemporary levels of 33%.

Americans know that this is more than a wardrobe problem. Surveys confirm that most people understand the connection between excess flab and heart disease and diabetes, and they're beginning to learn that obesity increases the risk for certain types of cancer. Unfortunately, the expanding American waistline shows we aren't changing our habits.

Retirement morbidity
There's another risk to obesity. Our food fetish can flatten our retirement. This is not the old warning about neglecting your savings and overspending on a Starbucks dulce de leche frappuccino blended creme. No, it's about the 680 calories in that venti-sized beverage. In other words, it's about behavior that can cause your health-care costs, direct and indirect, to devour your retirement income.

For an idea in today's dollars of what excess pounds can do to your budget, a recent article in Health Services Research offers a clue. Researchers found that "an elderly person who is overweight at 65 may spend $16,000 more and the obese person may spend $26,000 more than those who are a normal weight at age 65."

The risk extends beyond the individual to the entire nation. Another study, An Unhealthy America: The Economic Burden of Chronic Disease, makes this stunning observation: "Lower obesity rates alone could produce productivity gains of $254 billion and avoid $60 billion in treatment expenditures per year."

A bigger problem than Social Security
Social Security is a cornerstone of retirement planning, but many working adults fret about the likelihood of future cuts to the program. However, according to comptroller general David Walker, the nation's top accountant, their fears are misdirected.

In a CBS 60 Minutes interview, Walker explained that the Medicare problem is five times greater than the Social Security problem. He also points out that medical costs are rising at twice the rate of inflation. As the medical community constantly explains, the obesity epidemic is a major contributor to this dysfunctional dynamic.

Health-care investing as a remedy?
Of course, one way to look at the problem is as an investment opportunity. Abbott Labs (NYSE:ABT) makes the appetite-suppressant Meridia, while GlaxoSmithKline (NYSE:GSK) markets an over-the-counter version of Roche's fat-absorption reducer Xenical called Alli.

Acomplia, a Sanofi-Aventis (NYSE:SNY) drug available in 42 countries, hit a roadblock with the Food and Drug Administration in June and was withdrawn. The company said it would take the necessary steps to win future approval.

While the current crop of weight-loss drugs is limited, indirect investment opportunities extend across the health-care industry. It's sad to say, but companies with treatments for cardiovascular disease, metabolic syndrome, diabetes, and certain types of cancer all have increased sales opportunities because of higher obesity levels.

Ben Franklin and the Foolish bottom line
"Reader, I wish thee Health, Wealth, Happiness." So said Ben Franklin at the close of his 1735 edition of Poor Richard's Almanack. These are also the classic attributes of the perfect retirement. And it's no accident that health comes first. A retirement hampered by medical expenses and shortened by preventable illness is a beastly assault on happiness.

You may know your weight, but do you know your number in the body mass index? A score of 25 to 29.9 indicates you're overweight. A score of 30 or higher puts you in the ranks of the clinically obese. If your number is higher than 25, please read this publication from the Weight-control Information Network. Among other things, you'll learn that losing as little as 5% of your body weight may lower your risk for several diseases, including heart disease and diabetes. You can still grab a meal at the Golden Arches. But for the sake of your golden years, let McDonald's help you watch the calories.

To learn more about how your health plays a role in a comprehensive plan for retirement, take the next 30 days to look around Motley Fool Rule Your Retirement, free. You'll find all the retirement help you need. In fact, the many discussion boards exclusive to the newsletter service even include one devoted to Health Care & Wellness. Your journey starts here.

Fool contributor Doug Short (TMF Doug) is a happily retired Fool who divides his time between the Rule Your Retirement discussion boards and his favorite fitness center. He's tried all sorts of exercises and claims that the toughest of all is the two-hand horizontal extension: Put the palms of both hands on the edge of the dinner table and firmly push yourself away. Doug owns none of the companies mentioned. GlaxoSmithKline is an Income Investor pick. The Motley Fool has a disclosure policy.