Originally Posted by Robb Wolf
Body temp will decrease on IF. That can be good if you live in Chico in the summer and it's 45*C. Not so nice when its cold.
Robb made a good point the other day that got me thinking about IF's affects on thyroid output and body temp. Per his quote, "Body temp will decrease on IF." This makes sense, since body temperature (heat output) Is a direct measure of the amount of fuel (food and oxygen) being burned by the cells. Since no food is being ingested into your body, your metabolic rate (and therefore thyroid hormones should naturally dip. In other words, once you stop throwing wood in the fire, it will slowly but start to fade away. Of course, this is the logic behind eating six small meals every two hours to keep the fire (metabolism/thyroid output) constantly blazing.
We know a healthy thyroid function is not only crucial for improving one’s body composition, but just as important for graceful and vital aging. So if IF decreases body temperature below the normal metabolic rate (A normal metabolic rate will produce a waking temp of between 97.8 and 98.2 deg F), is IF as beneficial as we think it is?
While the verdict is still out, I think a simply test we can all do on our own can perhaps give us a better idea at how effective IF really is and its affect on thyroid function and metabolism. Perhaps knowing more about the changes in our metabolism we can have a concrete way of how IF affects the digestive and endocrine systems.
A few years back, my younger sister was diagnosed with hypothyroidism. Upon hearing this, I immediately grabbed interest and researched the subject as much as possible. At the time, I was trying to help her lose weight naturally with good ol' hard work and was afraid she would use the slow thyroid problem as a excuse to throw in the towel and turn over to the professionals. To make a long story short (after taking one test after another so every specialist known to her family physician could get their little hands in on the action) she gave up and went back to the natural route under my guidance. Anyway, this whole fiasco with the doctors lead me to spending much time learning about the thyroid and how it affects the body. Its actually quite overwhelming how complex the thyroid is and its relation with the rest of the body.
But...and I promise this post will end soon....but there was this simple test she did every morning (as soon as she woke up before getting out of bed) that was used to measure her thyroid function. Basically what you do is check your basal body temp immediately upon awakening and follow these simply steps:
1. Keep a thermometer by your bedside so you can take your temp before getting out of bed in the morning. (It is important to move as little as possible while taking your temp.)
2. Shake down the thermometer to read less than 92.0 deg (unless you have a digital, which I recommend.)
3. Upon awakening in the morning, take your auxiliary (armpit) temp for at least ten minutes.
4. Record your temp.
Repeat these steps for four days. (Menstruating women should record their temp on the second, third, fourth, and fifth days of their periods.) Calculate your average temp for four days. A normal metabolic rate will produce a waking temp of between 97.8 and 98.2 deg F. Temp below 97.8 may indicate, at the very least, subclinical hypothyroidism. Temperatures higher than 98.6 may reflect hyperthyroidism.
We know thyroid hormone increases the utilization of carbs and fat from food, and the rate of protein synthesis. It stimulates the appetite and the movement of food through the digestive tract. In the presence of thyroid hormone, muscle catabolism increases, which increases the resting metabolic rate (muscle burns more energy than fat). Thyroid hormone also increases the sensitivity of skeletal muscle to impulses from the spinal cord. (An excess of thyroid hormone is known to cause tremors, and a deficiency results in sluggish muscle response.) Thyroid hormone increases the uptake of oxygen into the cells, which speeds aerobic respiration. Finally, thyroid hormone actually increases the number of mitochondria within the cells.
As mentioned, the endocrine glands are in constant communication, not only with each other, but also with the nervous and immune systems. In conjunction with the pituitary gland, thyroid hormones influence almost every function in the body, as metabolism establishes the official temp at which systems operate. Because the thyroid gland's work involves interaction with many body systems, it is particularly sensitive to influences that can disrupt its proper functioning.
So what does all this have to do with IF?
Well, IF might be causing such a high stress on our body that PERHAPS and I used this loosely that fasting too much might reverse all the positive benefits of IF.
We know chronic stress affects the thyroid and endocrine function in a number of ways. The pituitary gland, the bodies "master gland," stimulates and controls the function of the adrenal cortex by secreting adrenocorticotropic (ACTH). If required to maintain a constant level of the major stress hormone cortisol in response to stress, the pituitary gland may over work. Too much production of ACTH may divert the pituitary from manufacturing other tropic hormones such as TSH, FSH, and LH. Cortisol production requires tyrosine, the same amino acid needed for the synthesis of T4. Excess cortisol production can deplete tyrosine levels, making it unavailable to the thyroid gland to make thyroid hormones. Stress depletes other important nutrients for T4 production, namely chromium and zinc. Excessive cortisol production from chronic stress also inhibits the conversion of T4 to T3 and the secretion of TSH. So the takeaway message (at least for me) is too much stress is obviously NOT a good thing over time.
So to FINALLY wrap this one up (sorry!) perhaps ALL our IF participants (and I know we have our fair share on this board alone)...keep a daily log of your resting temperature (remember first thing in the morning) and observe the patterns of higher temps on feed days vs. lower temps on fast days or steady temps throughout. Who knows what will happen.....perhaps this could be another tool from our BLACK (tool) BOX (inputs vs outputs concept) to use in our arsenal. Along with observing changes in body comp, performance, energy levels, sleeping, etc...we can track our body temp (very economical by the way!) and gauge other parameters such as metabolism and thyroid output.
Hopefully IF will become more popular, and in addition, the various influencers of thyroid metabolism such as stress and nutrient abnormalities will begin to become more recognized in the coming decade.
So what other IF's are up for checking their body temp every morning for the next few days? Curious to see the findings.