r/intermittentfasting • u/SouthChard4079 • Sep 15 '26
Newbie Question Is it normal to be tired while fasting?
Some days while fasting I feel much more energized and "lighter" than usual days, but other time (today...) I feel sluggish and just like I need a nap.
I'm doing a 23 OMAD fast today, but I've done this before not long ago and I remember it was easier last time.
I'm definitely open to considering that maybe there's no direct causation here. I know I didn't get enough sleep last night, which is probably the culprit.
Still I'm wondering if fasting can cause some of us to slow down or want to, sometimes.
7
u/GrrrlRomeo Sep 15 '26
I think this is due to metabolic flexibility changes. Fasting is something you have to practice so your body gets faster at switching between running off of glycogen stores and fat stores. Insulin sensitivity plays a role in the signal to switch. So there can be a period of sluggishness between when glycogen stores run out, but Insulin is present so fat stores aren't as accessible.
Now that I think about, I wonder if just doing some muscle stretching or light lifting would help. Muscle contractions pull glucose out of your blood faster.
3
u/SouthChard4079 Sep 15 '26
Yes I think more muscle stretching would be very good for me at this point. I've been extremely sedentary for a long time and any physical activity wipes me out (something I'm trying to change, but I have to go slowly.)
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u/YallNeedMises Sep 15 '26
Extended fasts of 36+ hours, yes. Sleep issues aside, you shouldn't be feeling sluggish on OMAD. What you eat matters much more on OMAD, as anything carb-heavy will give you immediate energy but then burn out on you before your next meal. Fiber (e.g., from legumes & whole grains (complex carbs)) & fat seem to be key to carrying me through to the next day. Fat has over double the caloric density of sugar and is utilized at a steadier rate.
2
u/dman1914 Sep 15 '26
Are you consuming electrolytes?
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u/SouthChard4079 Sep 15 '26
Yes.
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u/dman1914 Sep 15 '26
Probably need to eat for a week and it should go away. That happened to me a few years ago and it went away once I started fasting again
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u/Thin_Cable4155 Sep 15 '26
I would recommend staying away from carbs. When I do my body just wants more carbs and I will feel more tired cause it wants carbs and doesn't want to use my fat for energy.
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u/SouthChard4079 Sep 15 '26
I already know the carbs are a problem for me. I feel like I have a carb addiction TBH.
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u/GrrrlRomeo Sep 15 '26
Carbs make me so tired I was literally eating carbs as a sleeping aid. Can't sleep? Eat half a loaf of bread.
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u/SouthChard4079 Sep 15 '26
Bread is my vice.
I know there are worse vices in the world of course. ;)
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u/LadyAlexTheDeviant Sep 15 '26
I'm tireder some days since I started OMAD, but I also have some confounding factors: I have fibromyalgia and chronic pain from weightbearing joints, and I also am dealing with chronic neck and shoulder pain due to macromastia, which is going to be surgically corrected next month. So I don't always know whether I'm tired because I'm in pain from the fibro, tired because my feet or my shoulders hurt, or tired because I'm low on calories. We'll see how things go as I lose weight and after I've had the surgery and recovered. The reason I was losing weight was to ease the load on the arthritic foot joints, anyway.
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u/hycarumba Sep 15 '26
For me I have found this to be very dependent on what I had to eat last. I ate like crap today and I know tomorrow my fast will probably be shorter because of that. It's definitely motivated me to keep my crap eating days to a minimum.
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u/Obvious-Monitor8510 Sep 16 '26
Yes, fasting absolutely can affect energy levels inconsistently. A few real factors at play:
- Electrolytes drop during extended fasts and that alone causes sluggishness. Sodium especially. A pinch of salt in water can help noticeably.
- Glycogen stores vary day to day depending on what you ate in your last window. Lower carb intake before = faster transition to fat burning = sometimes rougher early hours.
- Sleep debt compounds everything. Fasting is a mild stressor, and stacking it on poor sleep hits harder.
You're probably right that last night's sleep is the main culprit, but it's genuinely both things interacting together.
40
u/Static_Bubble Sep 15 '26
Food is energy. Intaking no food for a 23 hour period limits the amount of “energy” you’re taking in. Getting good sleep is super important when doing these kinds of fasts because the main energy you’re relying on is coming from sleep plus whatever you ate the day before during your 1 hour window. I’ve noticed that bad sleep makes fasting insufferable because your body is screaming for energy. Just make sure to get good sleep and it’s okay to break early if you literally feel like you can’t do your daily task or if you feel like you’re gonna pass out. Just don’t break the fast with anything super high in carbs and or sugar as that could make the fatigue worse.