The science of human nutrition is known as dietetics. If you decide to study dietetics in college, you'll study nutrients and food, as well as anatomy, chemistry, genetics, and more.
If someone wants to be a nutritionist or registered dietitian, their field of study will be dietetics. It's basically the science of studying nutrition and then applying those principles to specific patients, clients, or groups. With knowledge of dietetics, you might go into public health, become a doctor, or advise people how to lower their cholesterol or blood sugar by modifying their diets, for example.