Type 2 diabetes used to be limited to over-40 couch potatoes who lived on junk food and soda, and were seriously overweight. But experts say there’s been a scary jump in diabetes among the younger, thinner, healthy-eating crowd.

Molecular imaging expert Dr. Jimmy Bell says it’s down to a condition called TOFI (“toffee”), short for “Thin Outside, Fat Inside.” In other words, you look thin, but your body behaves like you’re obese and fat that would normally build up under your skin gets packed between your abdominal organs, turning into dangerous visceral “belly” fat and causes inflammation that affects your liver, heart and pancreas, and lowers your insulin sensitivity, raising your risk for type 2 diabetes.

Why is this happening?
First, people aren’t exercising. Experts say that regular workouts are the only way to lose belly fat and even moderate exercise causes muscles to burn glucose at 20 times the normal rate.

Bottom line: Half an hour of brisk walking a day cuts your odds of type 2 diabetes in half.

Another risk factor: Yo-yo diets. Every time you lose weight by diet alone, you lose muscle and when you regain the weight, you gain only fat. Which means you’re losing the muscle mass that helps burn belly fat and control blood sugar.

One final reason younger, thinner people are at risk for diabetes: Hidden sugars, like high-fructose corn syrup in foods like low-fat salad dressing, cereal, and vitamin drinks. So, stick with healthy, blood-sugar balancing foods, like fruits, veggies and whole grains.