Here’s an interesting speculation: The microbes in bowel flora are metabolically active, generating heat. There are so many microbes inhabiting the human intestine that it is estimated that up to 70% of human heat (at rest) is generated by bowel flora.
In support of this argument, antibiotics have been found to reduce body temperature. Animals raised to have sterile intestines free of microorganisms also have lower body temperature. The pound or so of human bowel flora is therefore a virtual heat factory.
We know that feelings of being cold can be produced by common health conditions such as iodine deficiency, hypothyroidism, and anemia. Prescription drugs that relax (“vasodilate” ) blood vessels or block adrenaline can also yield feelings of cold (e.g., blood pressure drugs like ACE inhibitors and ARBs, beta blockers like metoprolol).
But should we add dysbiosis, small intestinal bacterial overgrowth, and prebiotic fiber deficiency to the list of factors that yield feelings of being cold? I think we should. In particular, nourishing bowel flora with prebiotic fibers is likely to be a useful heat-generating strategy, one that may provide improved tolerance to cold, less feelings of being cold.
Could this phenomenon explain why we often feel cold during an extended fasting period? Anyone who has fasted more than 24 hours is familiar with this effect that can be quite bothersome. Not eating means you take in no calories or nutrients, but it also means that intestinal microbes are also starved with resultant drops in bacterial counts and conversion to sporulating (spore-forming) hibernation mode. To prevent unpleasant feelings of cold during fasting, should we supplement prebiotic fibers, e.g., inulin/FOS powder, during a fast to preserve microbial survival and metabolism, while keeping us warm? That’s an interesting experiment we can conduct on our own.
Some other questions are raised by recognizing that bowel flora is part of human heat production:
- Can alterations in bowel flora composition and/or prebiotic fiber intake/composition account for better cold tolerance of some populations, e.g., Inuit living in circumpolar environments? Is there a specific probiotic species or prebiotic fiber(s) that we could supplement to improve cold tolerance?
- Does an increasing prevalence of dysbiosis account for the higher prevalence of feeling cold as we get older?
- Can the presence of cold intolerance (always feeling cold) or heat intolerance (always feeling hot) suggest dysbiosis or other disruptions of bowel flora composition?
Until we have answers to these and other questions, this provides yet another reason to continue to explore the issue of bowel flora and how to best put it to use. In the meantime, the Wheat Belly/Undoctored approach to bowel health remains the most rational way to cultivate healthy intestinal microorganisms and feed them with prebiotic fibers.
Another strategy for increasing the sensation of warmth, as well as reducing insulin resistance, blood sugar, and facilitating weight loss, are to adopt strategies that increase the proportion of brown fat in our bodies—a discussion for another day.