It’s politically incorrect to discuss weight. Anyone who comments is accused of fat-shaming. But here’s the truth: America’s expanding waistlines are causing health spending to spiral out of control. Obesity-related illnesses consume nearly a third of the nation’s health-care dollars.

Obesity is the culprit making health insurance unaffordable. The politicians won’t tell you that. (Too many overweight voters.) Most Democrats blame rising premiums on President Trump. Bernie Sanders blames corporate greed, insisting it’s time to outlaw insurance companies.

But numbers don’t lie: An obese adult uses 42 percent more health care than a healthy-weight adult, and a morbidly obese adult uses a staggering 81 percent more, according to the Robert Wood Johnson Foundation. Since health insurance isn’t sold by the pound, their extra costs are shifted onto everyone else

Blame obesity for another piece of disheartening news: Progress against heart disease, diabetes and strokes is grinding to a halt, according to the Journal of the American Medical Association.

It’s PC to criticize smoking but not being grossly overweight. Yet obesity kills more Americans than cigarettes and adds more to medical costs.

Some people become obese for genetic reasons, or lack of access to healthy foods or take medications with side effects that put on weight. But overeating and unhealthy food choices cause most obesity.

And obesity is linked to heart disease, stroke, high blood pressure, diabetes, colon and breast cancer, gallbladder disease and sleep apnea, for starters. Yet we’re supposed to stay mum about it.

Young people are encouraged to be fat and proud, because, according to Teen Vogue, being “fat means taking up space and demanding more.” Being fat “means saying f–k you.”

That feel-good message will doom young people to shorter, sicker lives.

No one should suffer discrimination at work or feel shunned in public because of their weight. But that doesn’t mean obesity is a healthy choice.

Already a staggering 40 percent of the nation is obese or morbidly obese, double the problem in 1980.

Worse, more than half of African-American women are obese. That largely explains their higher rates of hypertension, stroke, diabetes and other killer conditions. Yet typical of the movement to glorify fatness, African-American writer Ashleigh Shackelford says, “the more we realize that it’s not bad to be fat, the more we’re tearing down walls built by racism.”

‘Obesity kills more Americans than cigarettes and adds more to medical costs’

Wrong. Obesity is a main cause of the poorer health status of minority women. Normalizing obesity will only make the disparity worse.

Health costs are a top issue in the 2020 elections, and every candidate claims to have “a plan” to make health care affordable. These plans are shell games, shifting the costs from one group of people to another but not dealing with the biggest driver of costs — America’s growing girth.

Insurers should at least give a break to consumers who maintain a healthy weight. After all, nonsmokers pay less than smokers for coverage already.

This nation educated the public about the dangers of smoking and convinced millions to stop. We can do it again to combat reckless eating. Persuading Americans to shed their excess pounds, for their own health, is not body shaming.

What’s a shame is how much American taxpayers and insurance consumers are paying in added health costs because of the obesity epidemic.

Betsy McCaughey is a former lieutenant governor of New York and chairman of Reduce Infection Deaths.