If you've been eating "right" and exercising but still gaining weight — or can't seem to lose it — insulin resistance may be the hidden culprit. It's one of the most common yet underdiagnosed metabolic conditions, affecting an estimated 40% of American adults. And it could be the reason your body seems to be working against you. What Is Insulin Resistance? Insulin is a hormone produced by your pancreas. Its job is to help glucose (sugar from the food you eat) enter your cells