[h2odragon]

Nutrition isn't a "hard science" because people digest food differently, and that varies over time. We adapt. Your first week of a bean diet will be harsh but after the 3rd year you're probably ok. or dead. Some people wouldn't ever adapt to it.

There's "hard science" there but to throw a rope around the whole field is more of an exercise in faith, that there is One True Diet for All People.

[quantified]

Not at all. Adequate science would tease out all the suitable variables for each individual’s diet at any time and situation for their stage of life. Which will include the details of current internal biome, current infections, medical history of their digestive and other organ systems, metabolism cycles, and many more things. And for which outcome where outcomes compete: cancer likelihood, bone health, sperm count, mental dexterity, fat content, etc.

The fact that there are too many variables and that it’s overly challenging to adequately measure them, coupled with challenges in studying people (ethics, self-assessment blind spots, laws against various options) makes nutrituon a squishy science, neither soft (people stuff like economics or psych) nor hard.

[h2odragon]

Like weather forecasting but worse. Nicely put. "oobleck science" on this continuum perhaps.

[ksdale]

Does the fact that people digest food differently make a difference? I feel like the way food is digested is "knowable" in a way that physics is knowable, we just don't have adequate tools to measure all the complexity yet. As opposed to lots of things about sociology being "unknowable," like Asimov's Foundation being fantasy (probably).

In any case, I was attempting to make the point that hard science and soft science are anything but settled categories, which seems borne out by the responses.