“We don’t have a health care system in the United States. We have a sickness-care system.” That was presidential hopeful Marianne Williamson at a Democratic primary debate this summer. Since then, the question of what’s at the nature of our health crisis has continued to roil the left.

While other Dems propose to expand ObamaCare or, more radically, adopting a single-payer system, Williamson’s point puts people over policy: “What we need to talk about is why so many Americans have unnecessary chronic illnesses,” she said. As a Democratic socialist who supports Bernie Sanders, I applaud progressive efforts to implement Medicare for All. But lofty ideals aside, a large, heretofore unaddressed obstacle stands in the way of single-payer health care in the United States: us.

On the topic of health care, there are elephants in the room that Democratic politicians and liberal media dare not acknowledge: us, again. Because any real debate over single-payer health care must ask: Are we too fat for Medicare for All?

The numbers are, well, pretty heavy. According to the Centers for Disease Control and Prevention, 39.8% of American adults are obese, defined as a Body Mass Index of 30 or higher. The annual medical cost of obesity is estimated at $147 billion, with obese people costing, on ­average, $1,429 more than do those of normal weight.

Those figures are from 2016, and since then, the problem has only, er, grown: 2018 data show obesity stayed the same or worsened in every state. When combined with the less-severe “overweight” category, denoting a BMI between 25 and 30, the stats comprise a whopping 70.2% of American adults.

We are passing this epidemic to our kids: 18.5% of American children are obese. Unsurprisingly, the rates escalate as age groups get older, culminating in over one in five teenagers being obese. Our kids are growing out as they grow up, leading to dangerously overweight adulthoods.

By now, the list of diseases ­directly attributable to obesity are common knowledge. Obesity brings significant risk of heart disease, stroke, diabetes, high blood pressure, osteoarthritis. Certain cancers are linked to being overweight, as are breathing problems like sleep apnea.

Regardless of how healthy the population, implementing Medicare for All would be extremely expensive: Approximately $28 to $32 trillion over a decade, per the nonpartisan, nonprofit Committee for a Responsible Federal Budget. That would require significant revenue generation including, per Sanders, a middle-class tax increase.

This enormous expenditure is made even more daunting when obesity is considered, for two ­reasons.

First, illnesses caused by obesity are often chronic, meaning they must be continuously treated over extended, even lifelong periods. That makes them more costly both in medical expenses and lost economic productivity — important, as this decreases taxable earnings that would fund any single-payer system.

Second, signs point to obesity rates rising further. A recent Harvard study found that, if lifestyle trends continue, 57% of American youths will be obese by age 35. One 2012 report found that more than half of Americans could be obese by 2030; a more conservative prediction placed the 2030 rate at 42%, amounting to an additional 32 million obese Americans racking up medical bills.

As a socialist, I believe removing health decisions out of the hands of for-profit insurance companies is an admirable goal. Corporations and personal health are often in conflict, and the instinct to separate the two is understandable.

But even beyond political feasibility, one shadow looms over any attempt to adopt Medicare for all in America. That shadow is being cast by Americans themselves — and it’s only getting larger.

In 2015, Hillary Clinton, debating Sanders over the merits of socialist policies such as nationalized health care, notably remarked that “we are not Denmark.” She’s right. Denmark has an obesity rate under 20%, bolstering the economic viability of its single-payer system.

Ironically, any workable progressive single-payer system may require an historically conservative value: self-reliance. The financial feasibility of Medicare for All is ­already questionable. Unless Americans start taking care of themselves, the outsized costs may be too much for our outsized nation.

Christopher Dale is a writer in New York. Twitter: @ChrisDaleWriter