One of the case studies during Week 18 included a recommendation to supplement with zinc and vitamin A if a patient is not eating shellfish or liver, for a patient whose chief complaint was anxiety. Patient reported eating a low-carb Paleo diet. Would we assume the patient is not getting enough zinc from other food sources like meat and eggs? How long and in what amount would you supplement with zinc? Also, what’s the relationship between potentially inadequate vitamin A intake and anxiety?

Chris Kresser:   With a standard low-carb Paleo diet with no organ meats, probably zinc will be sufficient, but there are a lot of various conditions, like SIBO, that can reduce zinc absorption, so probably you want to test zinc levels to be sure, and we’re going to learn how to do that in the blood chemistry unit, which is coming up.

In terms of vitamin A, as you probably know, it’s not really present in significant amounts in muscle meats. So unless the patient is eating grass-fed dairy or organ meats, they may not be getting enough retinoic acid, the active form of vitamin A, and many patients aren’t able to convert beta-carotene, which is the precursor form in plant foods, into the active form, retinoic acid.

Vitamin A plays just an overall important role in the nervous system and the normal functioning of the brain throughout life. It’s involved in vision, the immune system, and skin health. Those are some of its more well-known roles, but it also plays a role in cognition, learning, memory, spatial functions, olfaction, and neuroplasticity and neurogenesis and just overall brain health in general. A lot of people don’t get enough vitamin A, and I’ve found particularly in patients with anxiety that it can be helpful. Cod liver oil is a great source because it also contains vitamin D and then the long-chain omega-3 fats, EPA and DHA, which are important for brain health as well.