Of course you're powerful—you're a nutrition wizard who harnesses the power to control what someone eats. Okay, well, you can at least help them develop a meal plan. If someone comes in to see you for a plan to help control their chronic kidney disease, you have the power to help manage their disease.
People who have this disease can't eat foods containing phosphorus, sodium, and fatty protein. Because those with impaired kidneys can't remove waste from their bodies, eating too much sodium-rich foods could cause their blood pressure to skyrocket, resulting in something as serious as death.
It's not a huge amount of power, but you can help those with kidney disease and others dealing with various dietary issues. You create diets tailored to the needs of your patients, and those diets can make a huge difference in their lives.
The one thing you can't make them do, though, is follow those diets. That part's on them.