Is it true that we have a second brain in our stomach?

Society is advancing technologically by leaps and bounds, and with it, the knowledge and understanding of ourselves and the world around us.

Modern medicine and genetic study are disciplines that continually challenge preconceptions, and thanks to new research, organs in our own bodies that we thought were already known are being rediscovered with new and fascinating properties.

Such paths lead us to such hilarious statements as “we have a second brain in our stomach”. A concept for all extraterrestrials, because we only know one nerve center in our body and it is located in the cranial cavity.

Like everything in the world of science and biology, we cannot conclusively state that this assumption is entirely true. Do we have a second brain in our stomach? Yes and no. Read on to find the correct answer to this question.

    A second brain in the stomach: between myth and truth

    It is clear that in order to understand the concepts to be covered in this opportunity, it is first necessary to cement the functioning and the general structures of the two bodies involved.

    1. About the brain

    The brain is the nerve center of nervous activity in all higher animals, including humans. It is responsible for thinking, memory, speech, language, reflexes and motor control of the body.

    In a typical brain cut, two well-differentiated types of tissue can be seen: white matter and gray matter.. The first presents this “faded” color thanks to the axons of neurons, these “collar-shaped” endings responsible for transmitting nerve impulses.

    On the other hand, the gray matter corresponds to the agglutination of the neuronal bodies, that is to say of the somes.

    In order not to get lost in the physiology of the lobes that compose it, we will limit ourselves to saying that the brain weighs about a kilo and a half and its crust contains around two trillion neurons. These figures speak for themselves of the great importance of this organ in the physiological framework of the human being.

      2. On the stomach

      The stomach, in turn, corresponds to the dilated section of the digestive tract between the esophagus and the intestine. Along with the duodenum, it is part of the infradiaphragmatic proximal part of this system.

      We could get lost in the physiology of this structural complex, but again, with some data, we are more than clear about the importance of the stomach to human functioning. This part of the digestive tract is about 25 inches high and has a capacity of over a liter in volume.

      It has a complex mucous membrane organized in a series of gastric folds, which are strongly irrigated and innervated. After all, the function of this section is the decomposition of foodSuch wide contact with the rest of the body becomes essential.

      As we have seen in these lines, the brain and stomach have little to do from a purely physiological point of view. Yes, both are an integral part of human functioning, but what makes some people claim to have a second brain in their stomach?

      Question of neurons

      The answer lies in the neuronal makeup of the two structures. We have already said that in the cerebral cortex there are about two trillion neurons, a figure that of course cannot be matched. However, plus or minus 100 million neurons can be found in the stomach environment, i.e. more than those present in the spine (or the same as those found in a cat’s brain. ).

      It is because of this neuronal grouping that some media claim that the stomach is our second brain. But what is the function of such a neuronal cluster in the stomach? Below we reveal it to you.

      1. Regulation of the energy balance

      Maintaining weight and body composition depend on hypothalamic (i.e. secreted by the hypothalamus) and non-hypothalamic factors, such as those produced in the intestinal tract that belongs to us here.

      The stomach alerts the central nervous system (CNS) of the individual’s nutritional state and energy homeostasis through distension signals and metabolic processes, i.e. presoreceptors and chemoreceptors. Various protein complexes such as insulin and leptin are generated in a modulated manner in the gastrointestinal tract depending on the individual condition, which they react with central neuropeptides modulating appetite.

      To summarize a bit the agglutination of the terms shown previously, we could say that the central nervous system and the stomach are jointly involved in the modulation of appetite and energy expenditure in the short and medium term. Investigating these correlations is not trivial, because obesity is a pathology of increasing concern in terms of health (it is present in 10% of the European population) and understanding the mechanisms of its emergence is one of the first steps to curb it.

      2. Modulation of emotional state

      It’s not all about neurons, as for example, preliminary studies seem to indicate that there is a correlation between the emotional state of the individual and his gut microbiota.

      We define the microbiota as the set of microorganisms (bacteria) associated in the colonies that have evolved with humans in a state of symbiosis. These, in the digestive tract, are responsible for promoting the synthesis of vitamins, digesting compounds of plant origin and encouraging specialization of the immune system, among others.

      What was not so clear until relatively recently is that the composition of the gut microbiota appears to modulate the development and function of the brain and even the moods of the individual. For example, preliminary research has shown that there is a marked difference in the microbiota between patients with depression and those who do not.

      Likewise, more and more studies indicate possible correlations between autism spectrum disorders (ASD) and dysbiosis (microbiota imbalance) in the digestive tract. Of course, there is still a long way to go to fully understand these interactions.

      In addition, 90% of the concentration of serotonin, a molecule that directly modulates human emotions, is found in the gastrointestinal tract. Neurons in the myenteric plexus synthesize it to control secretions, motility and intestinal sensations.

        3. Manifestation of stress

        As we have seen, the stomach is an important factory of neurotransmitters, engines of our mood. This portion of the digestive tract warns us, in different ways, that a situation of continuous stress over time is not at all sustainable..

        Hormones such as cortisol (produced in the adrenal gland), among other things, promote the secretion of stomach acid. Prolonged exposure to situations of stress and anxiety therefore leads to dysbiosis (imbalance of the intestinal microbiota) from which she suffers. This leads to intestinal dysfunction and less regeneration of the digestive mucosa among others.

        All these mechanisms of action and many others can generate twists, pain, gas, reflux in the patient and even promote the appearance of ulcers. Then the stomach warns us that we must reduce the tensions of the routine if they get out of control.


        As has been evident from the start, we can safely say that we do not have a second brain in our stomach. This denomination is the result of an enormous exercise in abstraction, because neuronal agglutination in the stomach system works very differently from that found in the brain mass.

        However, as we have seen, the stomach does, in a way, modulate moods, stress responses and of course an individual’s appetite and energy balance.

        Finally, we don’t want not end this opportunity without calling for the search for real knowledge and the leakage of information. When we talk about such matters, we cannot make forceful statements and it becomes necessary to be wary of those who do. No, “A microbiota imbalance does not cause autism”, rather, “the microbiota between people on the autism spectrum appears to be different than in people without this disorder, so the two could be correlated.”

        Information should be filtered with caution and reserve, because in the world of physiological interactions within the human body there is still a lot to know and to seek.

        Bibliographical references:

        • Dinan, TG and Cryan, JF (2017). Brain-gut-microbiota axis: mood, metabolism and behavior. Nature Reviews Gastroenterology & Hepatology, 14 (2), 69-70.
        • Kolb, B. and Whishaw, IQ (2006). Human neuropsychology. Pan American Medical Ed.
        • Martinez, JA and Solomon, A. (2006). Participation of the nervous system and the gastrointestinal tract in energy homeostasis. Journal of Medicine of the University of Navarre, 27-37.
        • Navarro, ANDREA (2009). Surgical anatomy of the stomach and duodenum. Digestive surgery, 1-22.
        • Ostrosky, F., and Neuropsicologia, DL (2010). The development of the brain. Neurosciences, National Autonomous University, 1-10.
        • Zacaries, M., Cadena, M. and Rivas, P. (2009). Structural modifications of the stomach and liver of Paralabrax maculatofasciatus (Steindacher, 1868) in situations of chronic stress. International Journal of Morphology, 27 (2), 425-433.

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