With swimsuit season right around the corner, a new science-based anti-diet book offers the most enabling advice we’ve heard this year: Those thunder thighs you hate so much might be key to long life.

“The Obesity Paradox” presents compelling evidence that those with excess baggage might be healthier and better able to fight off diseases than normal-weight counterparts. Conversely, the “thin and unfit” waifs have the worst body types for long-term health.

Though obesity remains a risk factor of “epidemic portions” — more, some researchers say, than smoking or alcoholism — associated with heart disease, stroke, Type 2 diabetes and cancer, cardiologist Carl J. Lavie argues that we need to rethink what we call “fat” and what we consider “healthy.”

Lavie, a cardiologist at the John Ochsner Heart and Vascular Institute in New Orleans, sums it up with one phrase in his book: “Looks can be deceiving.”

The term “obesity paradox” was coined in 2002 by Dr. Luis Gruberg and colleagues at the Cardiovascular Research Institute in Washington, DC, when they discovered — to their surprise — that overweight and obese patients had roughly half the risk of mortality of normal-weight patients following angioplasty, a procedure to unblock arteries in the heart.

Lavie noticed a similar trend in his patients recovering from heart failure. He published his findings in 2003, where he revealed that for every 1 percent increase in body fat, there was a 13 percent increase in overall survival.

“These findings created an uproar among my colleagues,” Lavie writes. “Unfortunately, the science world wasn’t ready to accept this observation in the early 2000s.”

But other studies backed the findings up. Overweight and moderately obese people also had better outcomes with other chronic diseases like kidney failure, advanced cancer and AIDS.

The studies are intriguing — but less clear is why.

Theories abound. For one, fighting off a disease requires using more energy. Patients who have more fat squirreled away might be at a natural advantage in battling chronic diseases.

The science world wasn’t ready to accept this observation.

Then there’s the role of genetics. While an overweight person might develop, say, heart disease because of his weight, a thin person who develops heart disease is more likely to have developed it because of a genetic predisposition. But, he writes, “A thinner person’s prognosis would be worse in comparison to a fatter person’s due to the power of those genetics.”

The obesity paradox, though, has had its fair share of critics. Some argue that these studies fail to take into account smokers, who are more likely to have lower BMIs. Some point out that the sickest tend to be the thinnest.

Lavie retorts that these criticisms don’t explain away the growing body of research that links higher BMIs to increased survival rates. Obesity — defined as having a BMI of 30 or higher — is “a crude way of determining one’s risk factors for obesity-related illnesses.”

BMI doesn’t take into account body shape, cardiovascular level or genetics.

And not all fat is created equal. Instead, unhealthy fat follows the real estate rule of “location, location, location.”

Abdominal fat, for instance, is associated with greater risks for diseases, while fat stored on bottoms, thighs, hips, or upper arms does not carry the same risk factors.

Carrying lower fat might actually help us combat cardiovascular diseases. Fatter thighs are linked to lower risks of metabolic syndrome, a cluster of risk factors that include raised blood pressure and high triglycerides.

Such findings have led some doctors to believe that liposuction of these areas might “increase one’s risk for heart disease.”

The more you sit no matter your age or weight, the sooner you’ll die.

But in general, when body fat increases, often so do muscle mass and strength, necessary in battling chronic disease. This leads to the essential divide between being “fat and being fat and fit.”

Weight and metabolic health are “imperfectly correlated.” Though a quarter of obese people are metabolically unhealthy, nearly the same percentage of normal people are also similarly unhealthy.

He cites two studies, one out of Canada and one conducted by the American Cancer Society, which both say unequivocally that the more you sit, no matter your age or weight, the sooner you’ll die.

“If you have to choose between being fat or fit, go for fit, even if it means being heavier,” he writes.

A study released in December by Curtin University in Australia, not included in the book, supports these assumptions. Researchers followed 8,662 people over 15 years and found that exercising significantly reduced mortality even in those with large waists and high cholesterol levels.

“Many heavier people with more body fat who remain as active as possible throughout the day can be fitter — and healthier — than thin people who sit all day.”

Fat or skinny — the worst thing you can do is sit still.