Nutritional yeast has been de-activated by heat processing, unlike "active" yeast which one would use for baking bread, or brewing beer and wine . So there's no risk of your stomach blowing up due to the yeast expanding and producing CO2 gas . It's popular among nondairy Paleo enthusiasts (and vegans) looking for a cheesy-tasting substitute.

As for yeast-related health problems, I suppose if a person has known sensitivity to yeasts / fungi (including mushrooms) then it might be prudent to avoid consuming nutritional yeast even though it's been de-activated


Here's an article about nutritional yeast, written from a Paleo perspective .. http://janeshealthykitchen.com/nutritional-yeast/

hth