The left arm is all you see of the mechanic. He is working under a car doing a main bearing job that he says will cost “about $200.”

As he grabs an oil filter near the left front wheel, he explains if the car’s owner had spent $4 on “one of these” with his last oil change, there’d probably be no need for a $200 repair job now. You then hear the roll of the dolly in that classic commercial first shown in 1972 as the gray-haired grease-monkey partially appears from underneath the car.

“Well,” he says matter-of-factly yet with a touch of sorrow, “the choice is yours. You can pay me now, or pay me later.”

That saying served as the FRAM oil filter slogan for more than a decade. It lasted so long because those words are more than a cautionary note about car maintenance.

They’re a reminder that in any aspect of life failing to act when you should act has consequences. It’s just that the consequences aren’t always immediate.

Adding all those extra pounds that make you obese, for instance, doesn’t occur overnight. Plus, they almost always result from things you can control.

So if you’re a part of the 42.5 percent of adult Americans currently obese (an increase of 283 percent since the debut of that FRAM oil filter commercial), you’ve decided, in a manner of speaking, not to pay the mechanic a bit now, but a boatload later.

And you will pay a boatload later. It’s just that the billing isn’t always immediate.

It’s this “delayed billing” for fat-dimpled thighs, triple chins, and bulbous bellies that makes the UK Biobank study of nearly 400,000 in the United Kingdom published in the March 2021 issue of Diabetologia noteworthy.

Along with the ominous increase in obesity, not only in the United States but also worldwide, there’s been a seemingly promising development. A fair percentage of the obese receive a clean bill of health metabolically.

Despite scoring 30 or higher on the Body Mass Index, their cholesterol, triglyceride, blood sugar, and blood pressure levels are not elevated as expected, but normal. It’s the elevation of two or more of these levels along with a 30-plus BMI that creates what’s called metabolic syndrome, a condition that compromises your overall health and significantly increases your risk of stroke, type 2 diabetes, and heart disease.

As a result, the term “metabolically healthy obesity” is now often employed to characterize these outliers and implies that it’s possible to be, in layman’s terms, both fit and fat.

While that may be true, the UK Biobank study suggests it most likely won’t be true for the long term, which makes the use of the term deceiving.

Researchers used 22 assessment centers throughout England, Scotland, and Wales to interview, weigh, measure, and check the blood pressure of nearly 400,000 participants following a self-administered, touch-screen health questionnaire. The information accrued allowed researchers to label the participants in one of four ways:

• metabolically healthy and not obese;

• metabolically unhealthy and not obese;

• metabolically unhealthy and obese;

• metabolically healthy and obese (what we’ll call fit and fat).

The researchers kept track of the participants for an average of 11.2 years and found out much about the fit-and-fat group over time that nicely aligns with FRAM’s “You can pay me now, or pay me later” slogan.

Compared to those categorized as metabolically healthy and not obese, the fit and fat were found to be at a substantially higher risk of diabetes, heart disease, heart failure, respiratory diseases, and dying for any reason during the course of the study. Even when measured against the metabolically unhealthy who were not obese, the fit and fat were still at a higher risk for heart failure and respiratory disease.

But here’s the real kicker: Five years into the study, the researchers found that more than one-third of the fit and fat were no longer fit, only fat. Two or more of their cholesterol, triglyceride, blood sugar, and blood pressure levels were now no longer normal, meaning they needed to be reclassified for the purposes of the study as “metabolically unhealthy and obese.”

They were now suffering from metabolic syndrome.

As a result, the four researchers who authored the study conclude “[u]sing the label ‘metabolically healthy’ to describe this [fit-and-fat] group in clinical medicine is misleading and therefore should be avoided.”

Moreover, “weight management could be beneficial to all people with obesity irrespective of metabolic profile. We suggest the term ‘MHO’ [metabolically healthy obesity] should be avoided in clinical medicine as it is misleading . . .”

So don’t mislead yourself. If you’re currently carrying a few too many pounds, or even enough to make you obese, but feel they have no adverse effect, you could indeed be right.

Right now.

But that’s a feeling that frequently fails the test of time.