Do microbiotas warm their hosts?

All natural animals and plants are holobionts, consisting of a host and abundant and diverse microbiota. During the last 20 years, numerous studies have shown that microbiotas participate in the ability of their hosts to survive and reproduce in a particular environment in many ways, including contributing to their morphology, development, behavior, physiology, resistance to disease and to their evolution. Here we posit another possible contribution of microbiotas to their hosts, which has been underexplored - the generation of heat. We estimate that microbial metabolism in the human gut, for example, produces 61 kcal/h, which corresponds to approximately 70% of the total heat production of an average person at rest.