You might have heard that your normal body temperature is 98.6°F.
But did you know that’s just the average? For you, a normal body temperature might be a little bit higher—or a little bit lower—than that.
Your age, your gender, your activity level—even the time of day—can influence your body temperature.
There may be another key influence, too. Recently, researchers have been asking:
How does weight affect body temperature?
In this article, we unpack the studies being done to answer this question. While we’re on the topic of weight, we’re also looking at how your body temperature affects your metabolism and sleep patterns.
What Is a Healthy Body Temperature
Technically, a healthy body temperature is 98.6°F. But in a healthy adult under the age of 65, anywhere within the range of 97°F and 99°F is considered normal—provided that it is your consistent average body temperature.
For children and babies, the average body temperature range is 97.9°F to 99°F.
For seniors (over the age of 65) the average is under 98.6°F.
As we age our body has a hard time regulating its own temperature. We have difficulty conserving heat, which means our body temperature is likely to drop as we get older.
The important thing is to establish what our own normal range is, in order to pinpoint any problems. We can call this our baseline.
The good news is: figuring out our baseline is easy—and free (if you’ve got a basic oral thermometer).
Taking our body temperature is easy, and it helps us monitor our bodies quickly. Your body temperature can give you some insight into your:
- Stress levels
- Circadian rhythm (more on this later)
- Metabolic rate
- General health
- For women: the menstrual cycle and ovulation
To work out your baseline, take your temperature at the same time every day. A good time to measure is first thing in the morning as soon as you get out of bed—before eating or drinking anything.
Take your temperature according to your thermometer’s instructions, and write down the number. As you continue you’ll start to notice a pattern, and over the course of a month, you should be able to establish clearly what your baseline body temperature is.
Quick note for our women readers: your body temperature can increase by up to 1°F from just before ovulation until the beginning of your next period. Some—but not all—women notice a spike in temperature just before ovulation.
Weight and Body Temperature
Many studies are being done to get hard evidence that answers the question: how does weight affect body temperature?
One study found that obese participants (classed as having a Body Mass Index of over 30) had a lower body core temperature during the day, and suggested that these participants could not create sufficient body heat. The difference in core temperature between the obese group and the control group was .63°F. Francesco Portaluppi explained that obese patients were unable to burn energy (stored fat) as heat when compared to a control group of participants within a healthy BMI range. This resulted in an average weight gain of 4.5 lb. per year for the participants with a lower-body core temperature.
Researchers involved concluded that reduced body temperature was common among obese participants and that the reduced body temperature put participants at more risk of becoming obese.
This study is unique because of the level of rigorous control used by the researchers involved. Participants had their temperatures measured starting 3 hours after they woke up. Their temperatures were taken rectally every two minutes for the rest of their waking hours. The environment was similarly stringent—they stayed in a temperature-controlled environment, had a fixed calorie diet, and minimal physical activity throughout the study. This means that any variables that could impact their body temperature were strictly controlled, and minimized their chances of influencing study results.
A study published by the International Journal of Obesity in 2018 states that body temperature is linked strongly to obesity markers in men and post-menopausal women. It also identified that there is no link between body temperature and obesity markers in pre-menopausal women, and suggests that this may be because of the menstrual cycle.
Another study, however, concluded that obesity was not associated with reduced body temperature in its participants, and suggested that there may be a link between gene mutations and co-morbidity in symptoms, which in turn lead to our bodies having difficulty regulating weight.
These findings were supported by another study, which concluded that it is difficult for researchers to identify only one key physiological difference between a 250 lb. participant and a 120 lb. participant. Essentially, there are so many differences in the systemic and chemical networks inside these two people, researchers have difficulty identifying just one cause as the root of the obesity issue.
The study did acknowledge a link between thermogenesis—our metabolic efficiency—and obesity. We’ll look at this now.
Metabolism and Body Temperature
Our body temperature has an effect on metabolism in two very distinct ways. The first of these is our metabolic rate. Our metabolic rate is how efficiently our bodies burn energy (stored fat) for fuel.
The second is metabolic health. Metabolic health is how efficiently our bodies are able to process carbs (carb tolerance), support healthy blood pressure, process insulin, and burn fat stored around our abdomen and internal organs (often measures as a waist-to-hip ratio).
The best way to look at the link between metabolism and body temperature, then, is to break it down into the two individual factors.
Metabolic Rate and Body Temperature
If you’ve ever been on a diet, you may have noticed that you felt cold all the time. So, how does metabolism affect body temperature? Research has uncovered that the two things are actually happening simultaneously.
As we lose weight, our metabolism slows down and our body temperature drops.
In one study, 8 adults—none of whom were overweight—were put on a low-calorie diet for 2 years. The diet caused an 18% weight loss in men and a 10% weight loss in women. When the participants started the study, they had an average body temperature of 98.6°F. When the study concluded 24 months later, they had an average body temperature of between 96°F and 97°F. As they regained weight, their body temperature returned to the average.
Similar results were found in another study—famously known as the Minnesota Semi Starvation Study. 32 men were studied to track the link between basal body temperature and metabolism—specifically the changes in their metabolic rate. The men were put through periods of semi-starvation and refeeding, to establish the link between lower body temperature and lower metabolic rate.
Metabolic Health and Body Temperature
Good metabolic health touches on factors like our carb tolerance, blood pressure, and insulin sensitivity. Generally speaking, good metabolic health can be identified by a daily body temperature that fluctuates throughout the day, but remains consistent when you compare each day side by side.
One study compared people with metabolic issues—high blood pressure, insulin sensitivities, etc.—to people who showed none of these symptoms. Researchers focused on the difference between the lowest and highest temperatures recorded in participants on a daily basis.
The group with poor metabolic health had an average temperature variation of less than 2°F throughout the day. The healthy participants’ temperature variation was around 3°F.
If you’re starting a new weight loss program, monitoring your daily variation is simple to do. Spend a few days tracking your temperature at specific times of the day. Do this again a month into your program, and again the following month. Getting to know the variation between your highest and lowest body temperature, and comparing it to past records, will give you a better insight into how your metabolic health is improving over time.
What Happens To Your Temperature at Night
We’ve touched on how our body temperature can—and should—fluctuate throughout the day. This fluctuation is all triggered by our circadian rhythm—the mastermind behind why we sleep when we do, why we wake when we do, and why we can have so much trouble doing either one of those things!
The Circadian Rhythm, and why it Matters
A circadian rhythm is a 24 hour physiological cycle in all living things. Humans, animals, plants, fungi—even bacteria—are affected by it. The cycle is driven by our hormones and chemical activity within our bodies, but it can also be affected by sunlight and temperature.
Your circadian rhythm is the driver behind when you sleep and eat, just like it’s the driver behind when wild animals sleep and eat. Researchers can measure its effects on our brain activity, hormone production, and cell regeneration.
Most of us know it better by another name—our body clock.
The Circadian Rhythm and Body Temperature
If we are healthy, our circadian rhythm tells us when to go to bed and when to wake up. It tells us this by altering our body temperature slightly to stimulate certain processes in the body.
Body temperature drops at night, to prepare us for sleep and the body’s natural recovery process. When your body temperature is at its lowest, you’ll be most tired. This normally happens in the very early morning.
When your body temperature is at its highest, you’ll be most awake. Interestingly, this normally happens around late afternoon to early evening.
Studies have shown that if you’re a morning person, your temperature peaks earlier in the day. Night owls experience their temperature peak later in the day.
This is another reason why monitoring our body temperature can help us take better control of our body and health. If you notice, for example, that your body temperature is peaking later in the day—no wonder you can’t fall asleep until the early hours of the morning. Building a routine around going to sleep in a cool, dark room at an earlier time can help reset your body clock.
Likewise, if you’re falling asleep at 6pm and you need to start pushing your bedtime back, there are ways to adjust your body clock there, too. Using brighter lights in the afternoon and evening are scientifically proven to help you push back bedtime.
When we look at how weight affects body temperature, we uncover some good news. Even though weight loss reduces our body temperature and slows our metabolism, these changes can actually help us live longer.
One study shows that fasting insulin level and body temperature—2 biomarkers of longevity—help slow the aging process in our bodies. So really, a slow metabolism might not be such a bad thing after all.