Do we control our fat, or does it control us? For generations, overweight individuals have been stigmatized and cast as lazy. But scientists are coming to understand fat as a fascinating and dynamic organ—one whose size has more to do with biological processes than personal choices. Through real-life stories of hunter-gatherers, sumo wrestlers, and supermodels, NOVA explores the complex functions of fat and the role it plays in controlling hunger, hormones, and even reproduction.