Basal Body Temperature: Tracking for fertility and metabolic health

Chasing symptoms. That feeling of knowing something isn’t quite right but not knowing how to troubleshoot. Late night searching on google after a long day of work for answers. I was in this vicious cycle when I learned about tracking basal body temperature. 

It was early 2015, just a few months after my second miscarriage. My menstrual cycles were all over the place and I was anxious to start trying for a baby again. I knew that I had to determine if my body was ovulating and learned that tracking your basal body temperature was a great tool to do this.

How to look for the clear temperature rise after ovulation, is something I had to learn. I discovered that if my temperature dipped at the end of my cycle, that indicated that I wasn’t pregnant and my period would soon show. If my temperature didn’t dip and continued to stay high, that could indicate a pregnancy. I found the whole process very fascinating.

What is basal body temperature?

Your basal body temperature (BBT)  is your body’s temperature when at rest. 

It can help women determine if and when they are ovulating, which is helpful for determining overall fertility. Many women track their basal body temperature as a natural way to avoid pregnancy as it helps you determine your “fertile window”. I highly recommend the book “Taking Charge of Your Fertility” for more information on this. 

Other things to keep in mind when tracking basal body temperature:

  1. The BBT should be taken around the same time every morning (+/- 30 minutes or so).
  2. Do not get up / walk around or get out of bed prior to taking your BBT first thing in the morning. It’s ideal to have your thermometer on your night stand, pop in your mouth when you first wake. 
  3. You need to have at least 3-4 hours straight of sleep prior to taking your BBT. If you wake at 5 am to go to the bathroom and then go to take your temperature at 7 am it won’t be accurate. 
  4. Alcohol consumption the night before can impact the accuracy of your BBT reading.

I’ve since learned that our body temperature is also an indicator of our overall metabolic health.

I dusted off my basal body thermometer a few months ago and set out to tracking again, as a means to determine how my nutrition, exercise, and stress levels are impacting my health.

A low body temperature can indicate a slowed metabolism, higher body temperature points to a faster metabolism.

What are signs of a slow metabolism?

Your metabolism is the process by which your body burns energy to support bodily functions such as breathing, heart beat, brain function and more. There are multiple ways to determine if your metabolism is sluggish:

  • Cold hands and feet
  • Low body temperature
  • Difficulty losing weight 
  • Slow digestion
  • Fatigue
  • Brittle nails 
  • Hair loss
  • Low pulse
  • Low sex drive
  • Cravings
  • Low energy / fatigue 
  • Brain fog
  • Anxiety / depression

The good news is that with focused nutrition, stress management and lifestyle changes, you can replenish and restore your metabolism. Many find that taking their basal body temperature is a helpful way to determine if their lifestyle & nutrition is working to their metabolism’s benefit.

How do you check your basal body temperature?

Pop a thermometer in your mouth first thing in the morning. You can keep track of your BBT in a fertility app such as fertility friend or you can utilize a paper chart to track your temperatures. I keep a note in my phone to track my body temperature. 

Can you use a regular thermometer to check your basal body temperature?

A regular thermometer will work or you can purchase a basal body thermometer which measures your temperature in tenths. Whatever you decide to use, make sure you stick to the same thermometer versus switching between different ones. 

Is basal temperature the same as body temperature?

No, basal temperature is the body’s temperature at rest. Once your body is no longer in a resting state and your body has been active, it’s no longer considered a basal body temperature, then it’s just your body’s temperature. 

Tracking body temperature for metabolic health

Curious to know how your metabolism is impacting your body temperature? Or maybe you have some of the hallmark signs of a slowed metabolism (such as cold hands & feet, fatigue, difficulty losing weight, etc) and you want to dig in further. 

Try this test: 

Check your BBT first thing in the morning. A person with a healthy metabolism should have a BBT of about 97.8 and 98.2 degrees. You can track it again about 20-30 minutes after lunch, it should be at least 98.6 degrees or higher. For most, you will be below these temperatures. 

When I first started working on healing my metabolism, my body temps were in the 97’s. I was coming off a diet full of polyunsaturated fats (PUFA’s, which are known to slow the metabolism), it wasn’t uncommon for me to have long periods of fasting, and I wasn’t eating enough nutrient dense calories throughout the day. I was over-exercising (and didn’t realize at the time) how much that was negatively impacting my metabolism. 

My favorite thing about tracking my temperature is it helps me determine if my diet is working FOR my metabolism or AGAINST my metabolism. If your body isn’t generating heat after a meal, you can dig in further and assess if you need more calories or if an ingredient in your meal isn’t “sitting well” with your body.

How does my metabolic rate impact my body temperature?

Your resting metabolic rate (RMR) is the rate at which your body burns energy when at rest. This is the energy required for your body to perform basic functions like breathing, circulating blood, and brain functions. RMR is often used interchangeably with basal metabolic rate (BMR). 

As your metabolism increases, so does your body temperature. “Working muscles cause the internal body temperature to increase. The physiology of blood transporting oxygen as needed  and removing the byproduct requires the metabolism of calories, or as we know it, food energy. This further translates into the more activity, the higher the body temperature, and the ultimate requirement an increase in the metabolism of more calories.” (1). 

Depriving your body of food can negatively impact your metabolic rate and body temperature.  “A fall in temperature is part of the body’s adaptive response to energy deprivation. During starvation both energy output and temperature drop.” (2). It’s the body’s way of going into a self preservation mode. A low body temperature is also associated with low thyroid function. 

This is why many supporters of pro-metabolic eating encourage a balanced meal every 3-4 hours and do not condone long periods of fasting. It’s not uncommon for pro-metabolic eaters to enjoy food 5-6 times a day, and bedtime snacks are not prohibited

What I’ve learned from tracking my basal  body temperature:

Temperature tracking was crucial for me when I was trying to conceive. It was also very helpful for me when we were trying to avoid pregnancy, as it allowed me to pinpoint my body’s fertile window and ovulation. I learned after tracking my temp, that I struggle with luteal phase defect, which often points to an estrogen / progesterone imbalance. Learning this helped me better pinpoint how to support my fertility.

I’ve since enjoyed tracking my temperature to see how my nutrition and fitness are impacting my body. My body temps tend to be lower the morning after I’ve had alcohol the night before, or if I eat a meal with PUFA’s (such as fried foods or take-out). I’ve noticed a dip in my temperature if I did an intense workout the day before. If my muscles are very sore and fatigued, chances are my body temperature takes a hit too. 

When you really take a step back, it’s incredible how we’ve been inherently designed with these “systems” or “tools” to help us better assess and discern if our body is functioning optimally. And the best part about a simple tool such as your body temperature, is that it’s a free test you can do on your own!