Has anyone taken their temperature while fasting and not fasting?

(Bob M) #1

I have been taking my temperature the first thing in the morning for a test of Fire in a Bottle’s succinate idea. It looks like this so far:

Fasting 32 hours or so did not lower my body temperature.

But I wonder if I took my temperature during a non-fasting day and a fasting day, whether there would be a difference? That is, maybe every hour or so while awake. Has anyone done this?

I’m going to try to do this, the day before and the day of fasting. That might be next week, but this is also right before Christmas, and we have guests for the holiday starting today. I’ll report back once I do this. The detriment: I’m using an under-the-tongue thermometer that takes forever to get to temperature. Minutes.


Interesting though mildly logical idea :smiley: Never crossed my mind. I want to buy a thermometer anyway (or not. what would I use it for? but my SO used it once in the last decade and we saw it on sale so why not?) and if I ever manage to do an EF again, I try to remember to take my temperature! I don’t expect any change as my body prefers stability and refuses to change, almost no matter what but maybe there is a difference…

I am looking forward to your surely way bigger experiences in the not so distant future! I am a curious one and it’s good when others experiment instead of me when I can’t even if we people are different…

(Bob M) #3

Well, last night, I wore a long-sleeve shirt and socks to sleep while fasting. That means I got cold, as I only wear these to bed when I’m fasting or sick. I’m trying to figure out if there is a real decrease in body temperature or something else is happening.

I’ll report back. Hopefully that will be next week, but we’ll see. The holidays is a difficult time to do tests like this.


I’ve never taken my temperature while fasting, but can relate to your experience of feet and hands getting cold. Not enough where I can’t hug myself, but being uncomfortable enough where I have to put on socks.

If I do another fast, I’ll try to remember to take my temperature if you find this information useful.

(Central Florida Bob ) #5

It never occurred to me to take my temperature; I just assumed when I felt cold I was cold. I should measure.

I’m taking a week off fasting because I’ve not been feeling well on fasting days. I tend to do my hour bike rides while fasted about 40 hours, and I’ve just felt low in energy. My speeds have been lower, and a few other signs of being low energy. My last fasting day, last Thursday into Friday morning, I had a really nasty leg cramp. I feel more back to normal after a few days of eating.


I used to go vampire cold, Especially hands and feet, sign of metabolic rate slowing.

(Bob M) #7

Well, I just happened to be fasting and taking my temperature, so I figured I could simply take my temperature more times.

I also read that people who said they had some type of event because of low blood sugar didn’t actually have low blood sugar. And I found that to be true when I had episodes I thought were caused by low blood sugar, but I was wearing a CGM and it wasn’t low blood sugar.

Now, I think a detriment to this will be that this only measures “core” body temperature. So, I might have to take some notes to gauge how cold my hands feel. As @lfod14 has stated, cold hands are one indication of metabolic rate slowing. When I was fasting a ton, I also got to the point where I got way too cold via my hands. They were freezing.

Lately, that’s not the case. But I’ll take some notes on how my extremities feel. Maybe I could attempt to measure them, too?

(Take time to smell the bacon) #8

I’m not sure that single temperature measurements would yield any useful information, since body temperature is fairly tightly regulated. If you were to measure a significant number of different spots on the body, getting readings of both core temperature and peripheral temperatures, that might yield a bit more information, however. My guess would be that core temperature would be pretty stable, and peripheral temperatures would be variable (I believe this is the reason that medical people are trained to prefer certain spots for temperature-taking, after all). Fever is a useful state for fighting disease, but it is not desirable over the long term for most of the body’s chemical processes.

I learned, with my pet rats, that their tails are their primary temperature-regulation devices, and that a rat with a cold tail is conserving heat, while a rat with a warm tail is shedding heat. Core temperature stays pretty constant, between 37.5°C/99.5°F and 38°C/100.4°F. My personal experience is similar, that I can be sweating or chilled, and my core temperature stays within a tight range (whether it be normal, or elevated from sickness). Since I don’t fast, however, I have never had an opportunity to see what effect fasting has.

(Bob M) #9

Well, when I was testing before this, and tested during the day instead of testing only in the morning, I got very low temperatures, as in 96.x. The complete table:

And I took other 96.x readings, but didn’t write them down.

There’s a two degree swing there, which I think is a lot.

I could be wrong, but I think temperature should fluctuate during the day, based on cortisol, activity, etc. For example, I assume if I take my temperature after a workout, it’ll be higher. I don’t know that, though.

Of course, I have no idea what happens if, say, I drink some cold water, then take my temp shortly thereafter. And this thermometer is frustrating to use, as it takes sooooooo long to register.

And I can get “hot” at times, particularly at night, for reasons I don’t know. Nor do I know if that’s my body temp going up, or I just “feel” hot.

It’ll be an interesting test regardless.

I will see what happens if I take my extremity temps via the under the tongue and IR thermometers.

(Take time to smell the bacon) #10

Yeah, two degrees does seem a lot. It’s a 2% variation from 98.6.

If the thermometer is oral, drinking hot or cold liquid will affect the reading, which is why they advise waiting a few minutes before taking your temperature. The adult human body is large, so it would take a lot of liquid for its temperature to affect our core. The only time I can remember this happening is when preparing for a colonoscopy: the mix they gave me to drink tasted dreadful unless it was chilled, so after consuming the first gallon, I started shivering and feeling quite chilled. But a cup of hot coffee in summer, or a cup of cold drink in winter, doesn’t seem to be enough to have a measurable effect.

My pure guess is that it’s peripheral temperature, not core, that we sense at such times. If we’re cold enough to shiver, that probably indicates a drop in core temperature. Symptoms of heat stroke would indicate the opposite.

Also, because of the poor circulation in my legs (runs in the family), my feet can feel freezing, while my upper body is sweating like crazy.

(Michael - When reality fails to meet expectations, the problem is not reality.) #11

Interesting. I frequently awaken in the middle of the night because I feel uncomfortably hot. I will toss off whatever covers are over me and go back to sleep, only to awaken a couple hours later feeling cold.

The only times I have my temp measured officially are mornings when I work. Walmart has a machine that uses an IR forehead scanner. Note, that this measurement is taken a couple hours or more after arising in the morning, consuming breakfast and commuting to Walmart from home. My temp is consistently 36.4 - 36.6°C, which translates to 97.5 - 97.9°F. On several mornings I have registered as low as 35.5°C, or 95.9°F. I have never registered 36.9°C which is 98.4°F.

Also of note now that winter has arrived. The main entrance to Walmart opens directly to the outside. The sliding doors do not work reliably and are generally wide open, allowing outside air to come into the checkout area of the store. Most of my fellow workers wear multiple long-sleeved shirts and/or heavy sweaters and/or coats. I wear a short-sleeved T-shirt and short sleeved casual shirt over it and generally feel comfortable. When my co-workers ask if I’m not cold like them I simply say I’m hot blooded and comfortable. I’ve always been this way, not just since starting keto.


I couldn’t buy a thermometer today.

I know people are often cold while fasting. I never was. Not even when I was starving in a cold room in winter and that’s odd as I usually am cold at a way higher temperature… Maybe I had too many problems without feeling cold…? Nevermind. I am not cold above 16C unless tired. Fasting has nothing to do with it but I never fast forcefully and if I am not very hungry, I don’t feel cold more than normal. (I never was very hungry while starving.)
I am always very dressed up in bed if it’s not summer, I need warmth there. Without socks? I am glad if one pair is enough. A fluffy, warm one. I use my thinner pairs for my walks outside. I dress warmer inside - even in bed sometimes - than outside (normally. of course there are exceptional cases). Moving generates huge heat in me. Especially in my hands for some reason. So cold hands merely tells me I am not moving. I tend to have ice cold hands inside so I started to wear my fluffiest winter gloves inside. I can’t wear them while walking as my hands get unpleasantly warm then, I tend to grab snow or metal objects in winter outside to cool my hands down (my SO’s hands are good too as they are super cold outside, in thick gloves. for a long while then his body starts to warm them up… the body has interesting things… my hands can’t stand gloves for 5 minutes outside).

Makes perfect sense to me… Unless one overdo fasts and then even the core temperature suffers. Maybe it happens in a smaller extent earlier…? I don’t know. Maybe even if it happens, it can’t be measured with a normal thermometer in normal ways…

To me, feeling cold is feeling cold shoulders for some reason. I need that part to be warm. Ice cold hands or feet, even thighs and belly may be uncomfortable but I don’t feel cold myself just because of them. (But if I am too warm, cooling down one part helps with the overall feeling. Feeling cold isn’t that convenient.)

It’s so annoying when one is freezing only partially :frowning: My worst part is my nose. I am pleasantly warm everywhere else but my cold nose bothers me. And we have no protein against that :frowning: (It’s an inside thing. -10C? My nose is okay. 18C inside? It’s silently screaming bloody murder.)

You people say some interesting things :smiley: Thanks for the rat tail info by the way.
At night… First I need the warmest dress/temp/whatever. Then I fall asleep and generate heat for myself and I couldn’t care less about the room temperature except my nose so let’s be warm as it can’t be good to spend the whole night under my thick blanket (I automatically hid my nose if it’s cold outside, I don’t even need to wake for that). And then morning comes… My room is as cold as it can be in this house, way colder than at bedtime… And I am super warm and could be naked (I wear my warmest pullovers inside normally), it wouldn’t matter, I have “sleep heat”. My SO has no idea about sleep heat, it’s not a thing for him. But so many things makes me feel warm.

(Bob M) #13

So, was not expecting body temperature to go DOWN after exercise (see 12/9, 7:42am):

BW = body weight workout, to failure each set.

Will have to confirm, but forgot to take after my 12/12 workout (about 1 hour BW followed by 20+ minutes jogging). Will see if I can remember to take for the next few workouts.

Edit: There’s a theory that lipoic acid causes a reduction in blood sugar. Or at least that’s what’s been reported by some. I have manipulated the protocol to not take lipoic acid before my workouts. I’m currently not taking at all the days I exercise.

Like this for instance:

Some might say this is good, but I think it’s bad. I think for someone like me, LC/keto 9 years as of 1/1/22, my body expects and produces higher blood sugar in the morning and during/after exercise. I may have to quit this regimen, as I have been taking lipoic acid first thing in the morning, and during/after my 12/9 workout, I had bad effects. I work out right after getting up, so we’re talking 1:20 with reduced blood sugar potentially, which isn’t good. I got a bit dizzy and had other negative effects. Then, I don’t eat for another 2+ hours after exercise, so I can’t make up that blood sugar.

That’s why I’m only taking lipoic acid when not working out.

(Bob M) #14

This is going to be harder than I thought.

Check out the temps 95.2, 96.2, 96.6, each taken one after the other. A 1.4 degree difference is a lot. Granted, these are still colder than what I started the day with, but still…

This is why I stopped taking blood ketones: I got so many values that seemed to be in error, it no longer told me anything.

(Central Florida Bob ) #15

The 95.2 and 96.2 are kind of scary to me. First off, that’s very low - assuming you’re in the middle of a day and not just getting up or just going to bed. A full degree difference four minutes apart, followed by another 4/10 of a degree in two more minutes? Sounds pretty suspicious that something else is going on, like maybe a bad thermometer?

As for values being all over the place, that’s part of the rational for following a strict protocol. Like ketones only being measured first thing in the morning, or some protocol like, “after bathroom, but before coffee.” Do a baseline of a week or so, then start the experiment. In this case, take your temperature at the same time and in the same conditions every day or as close to it as possible.

(Bob M) #16

Well, I’ve been taking it as soon as I get up. I have a lot of 96.x temperature readings. I just don’t show them.

When I test this for a day with no fasting and then a day with fasting, I’ll use a similar schedule.

This is supposedly a very good under-the-tongue thermometer. I find these hard to use, as it takes sooooo long to read, and I can’t tell exactly where it’s supposed to go. As far as I can tell, I’m doing this exactly the same each time, but maybe not.

For ketones, I have thousands of samples. They just don’t make sense.

(Take time to smell the bacon) #17

I tend to trust mercury thermometers more than the battery-powered ones, but that’s just me. Any thermometer needs to be properly placed. My thermometers all came with detailed instructions about where to place them for best results. The battery-powered ones are inexpensive and produce a rapid reading. The mercury ones have to be properly placed. I find that back under the tongue, as far back as the thermometer goes without causing pain, yields consistent readings. But you have to keep your mouth closed for at least a minute, in order to get a good reading, and a lot of us have trouble with that. Also, regardless of the type of thermometer, you should not eat or drink anything hot or cold for several minutes before taking your temperature.

(See what coming from a family of nurses does for one, lol?)

Your doctor probably has thermometers that can get a temperature reading from your ear or your forehead, but I would venture to guess that they are quite a bit more expensive than thermometers for home use.

(Bob M) #18

This one takes a looooong time to stabilize. I’ll see what happens. I’m not sure I can stick it back further into my mouth, but I’ll try tomorrow morning.

(Take time to smell the bacon) #19

It might very well already be in the right place. If it starts to hurt, don’t go any further! :grin:

(Bob M) #20

I think this might be more accurate than I thought, at least at certain times. These are the morning tests, where I get up, and take my temp within say 5 or so minutes of getting up. Not bad:

I’m not sure what caused those three different temps so close together, I’ll have to be more careful.

@PaulL I tried this morning to get the tip of the probe farther back, but it did start hurting. So I used the same spot I’ve been using.