Eating sugary foods and refined carbs like pasta, bread, sweeteners, and dessert don't cause weight gain just because they tend to be high in calories — these foods affect your insulin levels. Jason Fung, MD, a nephrologist (kidney specialist) and author of The Complete Guide to Fasting, explained to POPSUGAR that these foods spike your insulin levels. When insulin levels are high, it signals your body to store fat, which can lead to weight gain.
Eating these types of foods can also make you eat more in general, explained Susan Peirce Thompson, a psychology professor with a Ph.D. in brain and cognitive sciences. When eating sugar elevates insulin levels, it blocks leptin (the hormone that signals to your body that you're full). If your brain doesn't get the message that it's had enough, it'll signal to your body to keep eating.
Eating sugary foods also makes you want them more. That's because sugar overloads your dopamine receptors, leading to strong and insatiable cravings. In Thompson's book Bright Line Eating, she explained that this is why you eat cookie after cookie and still want more.
You don't need to ditch all carbs, though. Opt for complex carbs like whole grains, beans, veggies, and fruits. Langevin said to aim for three servings a day of whole grains, one to two of fruit, and one to two of legumes.