Nutritional yeast is a fungus, and despite how unappetizing that sounds, most of us eat fungi (such as mushrooms) all the time, so there’s no reason nutritional yeast can’t be included as part of a healthy Paleo lifestyle.
Nutritional yeast has long been touted by vegans as a safe, plant-based source of vitamin B12, but yeast does not naturally contain any B12. It is often fortified with it, along with other vitamins. If it’s not fortified, it doesn’t offer much in the way of nutrition, except for RNA, the consumption of which has been shown to reduce incidences of inflammatory conditions, such as gout.
Paleo and Anti-Nutrients
Despite the fact that it’s low in nutrients, nutritional yeast also doesn’t contain any anti-nutrients, which means it can be safely eaten without any adverse effects. There’s no nutritional reason to add it to your diet, but there’s no reason to avoid it either.
Mark Sisson gave nutritional yeast his seal of approval.