It's not just the empty calories you need to worry about when it comes to sweets and packaged junk food; it's how these foods affect your insulin. Jason Fung, MD, a nephrologist, explained that processed carbs and sugary foods such as doughnuts, crackers, pasta, and white bread spike your insulin levels, which can cause weight gain. Keeping your insulin levels low will help reduce your overall body fat percentage, and that means belly fat.
When eating sugar elevates insulin levels, it blocks leptin (the hormone that signals to your body that you're full) and overloads your dopamine receptors, which leads to insatiable cravings, explained Susan Peirce Thompson, a psychology professor with a Ph.D. in brain and cognitive sciences. In her book Bright Line Eating, she explained that this is why you eat cookie after cookie and still want more — eating sugar makes you crave it. Since sugary foods are so high in calories, and you tend to overeat them, it's no wonder eating sugar leads to weight gain and belly fat. If you cut down on these types of food, you'll definitely notice a difference in how you feel and how your belly looks.
Aside from being high in carbs and increasing your cravings, sugary foods also tend to be high in calories. That's not the only problem, though — eating them doesn't offer your body any nutrition, so you end up feeling hungry, which makes you eat more food overall.
You don't need to ditch all carbs, though. Avoid refined carbs and go for complex carbs like whole grains, beans, veggies, and fruits. Langevin said, "They break down slowly in the body because of their high-fiber content and help to keep blood sugar levels steady since they are digested slower. They're also richer in nutrients than simple carbohydrates." Aim for three servings a day of whole grains, one to two of fruit, and one to two of legumes.