What happens next?

How to get a phd in nutrition
Obtain a bachelor's degree in a science-related field.
The first major prerequisite you'll need is a bachelor's degree in a science-related field. The bachelor's degree will provide a foundation for all of the knowledge you'll learn as a graduate student in nutrition.
Generally, doctoral programs in this field look for completed coursework in nutrition or dietetics, so consider these as potential majors for your bachelor's degree. Some programs will consider people with a wide variety of educational backgrounds.