Welcome to the forum! 
Are you interested only in the clinical side of dietetics? I worked with dietitians in public health. They had their own office and a lot of their time seemed to be spent at their desk and attending meetings. The dietitians who worked with the family health teams sometimes attended groups for new parents to speak about mom and infant nutrition, perhaps a rare home visit, but definitely were not running on their feet all day. This was in Canada btw. I also imagine that dietitians who work privately or in clinics (ex. diabetes clinics) might get more sit-down time than those in hospitals, but I don't know if maybe that would be too much sit-down time :\ Alternately, if nutrition is something you would like to do, there is also an option of getting advance degrees in nutrition and teaching at the college or uni level - I don't know if that would be appealing?
Are you interested only in the clinical side of dietetics? I worked with dietitians in public health. They had their own office and a lot of their time seemed to be spent at their desk and attending meetings. The dietitians who worked with the family health teams sometimes attended groups for new parents to speak about mom and infant nutrition, perhaps a rare home visit, but definitely were not running on their feet all day. This was in Canada btw. I also imagine that dietitians who work privately or in clinics (ex. diabetes clinics) might get more sit-down time than those in hospitals, but I don't know if maybe that would be too much sit-down time :\ Alternately, if nutrition is something you would like to do, there is also an option of getting advance degrees in nutrition and teaching at the college or uni level - I don't know if that would be appealing?