The Medicare debate raging in Washington isn’t just a dispute over the role of government in health care. Nor is it simply a debate about how to rein in government spending in a time of budget deficit.

Rather, today’s Medicare debate is mostly a proxy battle over how we can pay for the astounding increase in the chronic diseases that are plaguing America’s health.

One thing is certain: The long-term viability of Medicare depends on a national commitment to preventing the onset of costly disease in the first place. And that must begin with an investment in primary prevention.

Today, almost one of every two American adults has at least one chronic illness. According to the Partnership to Fight Chronic Disease, virtually all Medicare spending — 96 cents of every dollar — is spent on chronic-disease care and treatment. More than half of Medicare beneficiaries are treated annually for five or more chronic conditions.

By definition, a chronic disease is “unending.” While it can be controlled, there is no cure. And in most instances, a chronic disease requires treatment for the remainder of the individual’s life.

Paradoxically, chronic diseases such as heart disease, stroke, cancer, diabetes and arthritis not only are among the most common and costly of all health problems in the United States but also are among the most preventable, according to the Centers for Disease Control and Prevention.

Chronic diseases, in fact, are largely attributable to just four modifiable behaviors: lack of physical activity, poor nutrition, tobacco use and excessive alcohol consumption.

Primary prevention — that is, deterring the onset of disease before it occurs by engaging in beneficial lifestyle behaviors such as regular exercise, healthy eating, avoidance of tobacco and other controlled substances, stress management and routine medical exams — is the most efficient, cost-effective way to stem the tide of chronic disease that wastefully consumes billions in Medicare spending each year.

According to the CDC, 80 percent of heart disease, stroke and Type 2 diabetes — as well as 40 percent of cancer — could be avoided if people simply exercised more, ate more healthfully and stopped smoking. Statistics from the Exercise Is Medicine initiative indicate that at the proper moderate intensity, regular exercise alone can lower the risk of colon cancer by more than 60 percent, can reduce the risk of developing Alzheimer’s disease by one-third and can decrease depression as effectively as medications or behavioral therapy.

Health Affairs recently released a sobering new study indicating more disease and earlier mortality ahead for today’s younger Americans. According to the study abstract, a new “three-dimensional” method of forecasting vital health statistics — which takes into account the delayed effects of the health risks being accumulated by today’s younger generations — suggests future death rates and health care expenditures could be far worse than currently anticipated.

The study’s authors go as far as suggesting that policymakers adopt this more robust forecasting tool and redouble efforts to develop and implement effective obesity-related prevention programs and interventions.

They are right. If we are to control the cost of treating preventable illnesses, our nation’s health care policies must focus on preserving health. This requires a commitment by Congress and the administration to realign the health care delivery system, to promote programs that prevent disease and to create encouragements and incentives for Americans to engage in healthy lifestyles — of which physical activity is a critical part. We must create a national public policy and health care environment wherein our citizens are supported in their efforts to make healthy lifestyle choices.

In a resource-strapped environment, large spending on preventable chronic diseases crowds out the ability to spend limited dollars on other medical issues that would — in the long run — serve a greater good in creating a healthier, more prosperous America.

The 96 percent of Medicare dollars already spent on preventable chronic diseases is a fait accompli. But if we act with urgency to embrace and support prevention and healthy lifestyles in America, we can give our nation’s youth a better shot at a future of good health.

And if we’re successful, they’ll live long and well, and they will benefit from an affordable Medicare system — however it might look in the future.

Joe Moore is president and CEO of the International Health, Racquet & Sportsclub Association.