No matter what she tried, Rachel Meyers, who weighs 103 pounds, just couldn’t put on weight.

So the 5-foot-2 single mom would eat whatever she wanted — and that often included sugar- and carb-heavy meals from chain restaurants.

“I’d get the cheesecake pancakes with a milkshake five times a week,” Meyers, 28, says of her daily trips to IHOP. “Most of the waiters wouldn’t give me a menu — it was like, ‘OK, see you tomorrow.’”

But when the Chelsea-based Meyers went in for her regular checkup at the Ryan-NENA Community Health Center in the fall of 2014, she got a shock.

There, Dr. Michelle Soto told Meyers that her blood-sugar levels were similar to those seen in “someone who’s obese — someone who’s 200 pounds.”

An A1C test — a common blood test used to diagnose Type 1 and Type 2 diabetes — revealed that Meyers had a pre-diabetic blood-sugar level of 5.8. (5.6 or less is considered normal.)

Meyers is “skinny fat” — a person who appears to be in great shape, but whose full health portrait tells an entirely different story.

While a heavy person with a high body mass index (BMI) and evenly distributed fat can be perfectly healthy, that’s not necessarily the case with people of normal weight who have excess middle fat often invisible to the naked eye.

According to a study published last year in the Annals of Internal Medicine, people with normal BMIs who carried fat in their midsection (known as central obesity) were at increased risk of both cardiovascular and overall causes of death compared to those who were obese or overweight.

“Those with normal BMIs may have a false sense of reassurance without knowing their fat distribution,” noted the study’s author, Dr. Francisco Lopez-Jimenez, director of preventive cardiology at the Mayo Clinic.

Meyers has an 18.6 BMI, a healthy-sounding stat that would make most people sigh with relief.

But that figure doesn’t take into account fat that can accumulate within the abdomen and coat the organs. Known as “visceral fat,” it’s thought to be more harmful than fat below the skin — and is linked to insulin resistance and high cholesterol. (To measure body fat distibution, divide your waist measurement by your hip measurement; a ratio greater than .9 for men and .85 for women is excessive.)

For Meyers, years of chugging sweet Snapple iced tea and gorging on McDonald’s four times a week had taken its toll.

“I was trying to gain weight, but not realizing that I’m damaging myself,” says Meyers, a full-time college student at Borough of Manhattan Community College, where she studies film and TV production. “I look thin and healthy on the outside — with a flat stomach — but my organs are all messed up.”

Dr. Jeffrey Morrison, who practices integrative medicine and nutrition at the Morrison Center in Midtown, says that a diet low in protein and high in carbohydrates is to blame in such cases.

“I have certainly seen patients with ‘skinny fat,’ ” says Morrison.

“Since they are deficient in protein, their muscle is catabolized [used for energy] and they become thin in appearance. At the same time, all of those carbs are stimulating insulin production, which causes fat gain. The classic blood test shows elevated triglycerides on their cholesterol panel,” he continues.

It’s not just Meyers’ health that’s in peril. Her daughter, Anayjiah, 9, is also pre-diabetic, and Meyers says doctors are extremely concerned about the fourth-grader.

Meyers was only 11 when she lost her own mom to cervical cancer. And she doesn’t want to be another cautionary tale: If left untreated, Type 2 diabetes can lead to vision problems, heart disease and amputation.

“I’m afraid I won’t be here for my daughter,” she says.

Thankfully, her and her daughter’s prediabetic conditions can be treated by maintaining a diet low in carbs and sugar — and corrected within months of following it.

Now it’s fruits and veggies for Anayjiah, and no middle-of-the-night Oreo bingeing for Mom.

Today, Meyers sounds a warning not to be fooled by outwardly skinny people: They’re the ones who potentially face the most danger, because they think they have carte blanche with their diets and that they can skip checkups.

“I wish someone told me 10 years ago that just because you’re thin doesn’t mean you can eat anything you want.”

Meyers isn’t the only skinny person with unhealthy eating habits. This model’s diet includes a mountain of cheeseburgers: