But the other part was gaining insight into the science of obesity, in part, thanks to meeting Ania M. Jastreboff, MD, PhD, a physician-scientist and founding director of the Yale Obesity Research Center. SELF spoke with Dr. Jastreboff about what science still needs to understand about obesity and GLP-1s and her powerful collaboration and friendship with Oprah. SELF: In your book, you write that a person’s weight is determined by their “enough point.” What does that mean? There are nutrient-stimulated hormones in the body, and they inform our brain, I’m hungry, I’m full, I’m storing this much energy, I’m storing this much fat. So if that’s our beautiful biology, then why do nearly half of Americans have obesity?