Energy balance

Deficiency in all three beta-adrenergic receptors ($\beta$-less mice) causes a complete failure of diet-induced thermogenesis, resulting in extreme obesity when consuming a high-calorie diet, despite normal food intake.

This research highlights that your body's ability to burn calories (thermogenesis) in response to eating is a critical biological defense against weight gain. If this system is impaired (genetically or otherwise), you may gain weight easily even if you don't overeat. While this specific genetic defect is rare in humans, it underscores that weight management involves more than just calories in vs. calories out; it involves your body's metabolic response to food.