Digestion uses a lot of calories (ever notice you get tried after eating a giant meal like Thanksgiving?) and generates heat. Something like 10% of the calories you consume goes into digestion. People who do calorie deficient (different than fasting) will notice their metabolism decrease. Fasting means you’re not getting the heat output from digestion. If you’ve been losing weight, you’re basically shedding insulation that would have kept you warm.
I do notice I get colder than usual and hot black coffee or tea helps me when I’m feeling too chilly.
Try exercising like lifting weights or walking, that will help boost your metabolism and warm up.
Is your heater on? Only kinda kidding :)
I would recommend some exercise if you’re already wearing layers. How does last week compare to this week in regards to your eating window? Was it warmer last week where you live? Was there more sun?
Are you warmer after eating? In the evening? If you can time your eating window to when you feel most cold, then maybe you can take advantage of the extra heat from digestion by strategically eating when you’re feeling the most cold.
I hear you about being freezing during fasting: I end up bringing my laptop to bed to huddle under the covers. I’ve seen others mention the same on this forum over the past few years.
I haven’t noticed an improved resistance to cold post-fast, but that’s super interesting. Now I’ll try to pay attention!
You may have some sort of medical or genetic condition that you’re not aware of causing you to feel cold related to how your body reacts to eating food.
Maybe whatever mechanism in your body thay causes you to feel cold while eating doesn’t occur when you water fast. I have no idea what that mechanism would be but it’s definitely not the norm.
If it’s immune system related… water fasting may cure it overtime through autophagy.