So Are questions regarding the assessment of nutritional products considered on-topic? was for some reason closed as a duplicate of Should title be "Fitness" instead of "Fitness and Nutrition"? which in no way answers what is on-topic and what isn't.
Then there's Are questions regarding the assessment of nutritional products considered on-topic? which also does nothing to really give a finite answer to a new user.
Looking at the site and main page it seems very unclear. I get what's definitely on-topic, that's easy. But where the line for the off-topic is gets incredibly blurry.
What are side effects of excessive kefir usage? -- Dangers of kefir stated for weight loss got closed.
Are commonly-accepted health risks of steroids real? -- Health risks of Steroids with no stated fitness reason is open.
How dangerous are steroids (injections)? -- Another almost duplicate question on Steroids with no stated fitness reason is open.
Are there health risks associated with protein shakes? -- Are there health risks associated with Protein Shakes, no stated fitness reason is open.
Meal Replacement Shakes - Why aren't they healthy to consume for all nutrition? -- Meal replacement shakes with no stated fitness reason is open.
Is egg white powder a good alternative to whey protein? -- Egg white powder with no stated fitness is closed.
How to avoid Creatine dependence? -- Creatine alternatives with no stated fitness is open.
On the Graphic Design Stack Exchange for topics that are borderline we have established guidelines posters must follow when asking:
I'd really encourage the established members and moderators to decide what is on-topic and off-topic regarding the nutrition, create guidelines, and enforce them.