How would you address normal TSH, but low T4?    Well, the first thing I'd do is I'd look at your T3. For those of you who aren't familiar with thyroid hormones, TSH tells your thyroid to make thyroid hormone. T4 is the precursor. T3 is the active hormone.    If your TSH is normal, that means that your pituitary is receiving the proper messages from your thyroid gland.   But if your T4 is low I would ask; is your T3 normal or high? If your T3 is high, then you're probably just converting it very rapidly. If your T3 is low —  then even though your pituitary appears to be receiving the right signals, you're not making enough thyroid hormone.   In fact, it would become unclear whether your pituitary is actually making the right signal because if your T4 and your T3 are low, your TSH should be high because your pituitary should be saying, "wait a second, T4 and T3 are low, so I need to make more of the message, TSH, to tell the thyroid gland to kick into gear."   If T4 and T3 are both on the lowish side and the TSH is normal. I would then look to the pituitary.   In terms of nutritional issues, I think the big things that you're looking at are calories, carbohydrate, and body fat — because the pituitary is overwhelmingly asking the question, do I have enough energy in the short term and the long term to engage in the health-promoting, long-term investments that thyroid hormone governs?    Those are many, like all the biological peacocking, like making nice hair, and making nice skin, and making things look nice. It’s also protecting your tissues from damage. Then the big, thing is if you're in the right age bracket, is fertility.   So, if your pituitary is not making as much TSH as it should, then that's basically saying your brain perceives that you don't have enough energy on hand, and that means either your body fat's too low, your calories are too low, or your carbs are too low —  because those are the big signals that your brain is going to use.   As mentioned int the Nutrition in Neuroscience series that I did all of these releasing hormones that govern the endocrine system require copper, vitamin C, zinc, and glycine.    So bottom line is; look at is body fat, calories, and carbs. But the next layer to peel back would be; vitamin C and copper especially, and zinc and glycine in the background.   This Q&A can also be found as part of a much longer episode, here:https://chrismasterjohnphd.com/podcast/2019/02/09/ask-anything-nutrition-feb-1-2019/    If you would like to be part of the next live Ask Me Anything About Nutrition, sign up for the CMJ Masterpass, which includes access to these live Zoom sessions, premium features on all my content, and hundreds of dollars of exclusive discounts. You can sign up with a 10% lifetime discount here: https://chrismasterjohnphd.com/q&a