T4 is the inactive version of the thyroid hormone and as a precursor for the ‘active’ version, T3. T3 is the catalyst for weight loss, warm limbs, and a good mood. T4 makes up about 90% of the thyroid but must be converted into T3 before it can be used. However, if your body is stressed or on a calorie-restricted diet, a signal is sent to change the ratio and you can produce more reverse T3.
Reverse T3 is an inactive metabolite of T4 and provides a mechanism for your body to slow down metabolism in order to save energy. Basically, T3 provides a feedback system to keep you in balance under normal conditions. However, if you are stressed or on a calorie-restricted diet, a signal is sent to change the ratio and you produce more T3. This will slow down your metabolism by raining in the production of T4. This means you continue to have low thyroid (hypothyroid) symptoms.
Repeat after me: Stress makes thyroid stimulating hormone less reliable.
I use my accurate thermometer every morning to measuring my waking (basal) temperature to track my cycle so I know when I’m ovulating and how my health is. Low body temperature is sometimes correlated with low thyroid. Normal body temp is between 36.5 and 36.8 but depending on your cycle and other facts this can change things a little. Never the less, if your basal temperate is constantly below 36.5, you have low thyroid function  — hello to ME.
As mentioned earlier, long-standing stress causes you to make less free T3, the active thyroid and too much reverse T3, which blocks thyroid-hormone receptions. The adrenal glands secrete cortisol and that regulates your response to stress. Countless studies have shown that chronic adrenal stress impacts the functioning of your hypothalamus and pituitary glands which directs the production of your thyroid hormone. Stress enters your body via parts of your brain and your response to stress is via a hormonal control system called the hypothalamic-pituitary-gland (HPA) axis which sets off a chain of reactions through your body of fear. Too much stress throws off the balance of the hypothalamic-pituitary-thyroid and there is a proportional decrease in thyroid function. Also, when your body is flooded with cortisol, this slows down the HPA axis , thyroid hormone and thyroid production.
In a nutshell: When your cortisol goes up, your thyroid hormones go down.
Studies have shown that going too low carb can actually disrupt the thyroid for some people. Additionally, women often do much better with some carbs in our diet because of our hormones. Cycling in and out of ketosis is a great way of being on a mostly low carb diet, without disrupting your lady bits.
Dr Alan Christianson conducted a clinical trial with people that were in some stage of adrenal fatigue. The idea is that carbs elevate blood sugar more than protein and fat and when you elevate blood sugar, you cause your body to make more insulin to manage the increase. Kind of like a seesaw (as one goes up, the other comes down). He basically got people to eat healthy carbs like root veggies at night because it was supporting the shutdown of cortisol which allows you for a better night’s sleep. In a nutshell à lower carb meals allow cortisol to stay high and higher carbs push cortisol down.
This is where having a low carb breakfast is great because it keeps cortisol high, but having some healthy carbs at night can blunt cortisol making your sleep more restorative and allowing your body to rest and repair (hello increase temp!!). Having quality sleep not only improves your thyroid but is also a long-term factor in weight loss, inflammation and overall health.
Having high cortisol also blocks or lowers the production of thyroid hormones, sex hormones, growth hormones and melatonin (sleeping hormone). So not only am I helping my thyroid but I’m also helping my body to feel relaxed, safe and balanced so that I can get my period back as I haven’t had it since before my accident (due to stress).
Estrogen and progesterone are made in your adrenals and your ovaries but will be shunted towards the production of more cortisol when a woman is under chronic stress. This is because your body thinks you are running from a saber-toothed tiger, and so clearly it is much more important to boost your cortisol and adrenalin so you can run fast, rather than having a baby. (You can’t really have a baby and be in danger at the same time now can you??).
Additionally, when your stress is high you can lose your period (like me) or get bad PMS. When stress is high, cortisol rises and progesterone production is lowered.
This might explain it well:
Okay, so my experiment:
I ate sweet potato at night with dinner covered with LOTS of coconut oil, cinnamon and some salt (so fricken YUM) and then I would measure my basal temperature the next morning. My app allows me to write notes in when I’m filling in my temperature so I would make sure to record that I ate sweet potato last night with dinner. All the increases you see here from the red line forward I was eating sweet potato. Before this, I had undergone my surgery and the stress was REALLY creeping up on me from not having my independence, lack of sleep, and just overall emotional crap. All the dips you see are the nights that I didn’t eat sweet potato. – funny, huh?
NB: My cycle is 100 days long right now so just excuse that haha
I even tried other factors like not having sweet potato some days and doing two meditations in the day/ having a stress free (lol jokes that never really happens) and my temp didn’t rise!
Whether it is the carbs or the vitamin A (it’s important for your thyroid and besides chicken livers, sweet potato is a great source of vit A), I’m not sure of, but I’d encourage you to try it out and see if you notice a difference. I’m still on the journey of trying to heal my thyroid back into the healthy range, but sweet potato is seriously helping (I think it’s also helping my soul haha). Here is a study showing that having HEALTHY carbs at night actually can induce weight loss.
This information is not meant to treat or diagnose, I am simply sharing what has worked for my body, and I encourage you to experiment with your body in a safe and healthy way.
 Sund-Levander M, Forsberg C, Wahren LF. “normal oral, rectal, tympanic and axillary body temperature in adult men and women: a systematic literature review.” Scandinavian Journal of Caring Science 16(2)(2002): 122-28
 The HPA axis is like a PSA to your body. Your hypothalamus tells your pituitary gland (the boss of your adrenals) to tell your body there is fear and you need to run for your life. Normally, your HPS tells the adrenal glands to increase cortisol production and then via a feedback loop, the increased cortisol stops the HPO which settles down until the next event. However, with overexposure to stress, the cortisol is so busy flooding your blood that it forgets to remind the HPA to calm down. As a result, your HPS keeps telling your adrenals to make more and more cortisol and this leads to high blood pressure, high blood sugar and a poor immune system.