While a scientific or engineering background might demonstrate capability to understand another scientific field, that doesn’t replace the near decade of education people in that field have.
I would absolutely trust a physicist (who has done actual empirical lab work) who has deeply studied a problem in the nutrition space over someone conventionally trained in nutrition.
You may be stunned to see how little numerical sense so many in the medical field have. And as someone who grows medicinal plants and follows that literature closely, I read tons of papers in that space. It is full of experimental design flaws and dubious correlations.
I have worked on a medical device that went through clinical trials.
A dedicated physicist who self-taught medicine would allow hoofs to be zebras, not horses, some % of the time.
Doctors need practice in the hospital and do an excruciating amount of rounds surrounded by senior experts.
Nutritionists? No.
Given a nutritionist who has studied the books and gotten a degree and a physicist who has studied the books and hasn't gotten the degree I would be hard pressed to choose the nutritionist