Quick Summary Yes, an underactive thyroid can cause fatigue and weight gain. When the thyroid doesn't produce enough hormones, your metabolism can slow down, leaving you tired, cold, constipated, or struggling with changes in your weight. But thyroid disease isn't the only possible explanation. Here's what you should know: Hypothyroidism can cause fatigue, brain fog, dry skin, constipation, and modest weight gain. Hashimoto's disease, an autoimmune condition, is the most comm

You’re eating better. You’re exercising. Maybe you’ve even cut calories, stopped eating late at night, and started walking more. But the scale barely moves. Or worse—you keep gaining weight. It’s frustrating. And after a while, it’s easy to think: “Maybe I just need more willpower.” But weight regulation is more complicated than willpower or calories alone. For some people, one piece of the puzzle may be insulin resistance. Insulin resistance can make it harder for your bod