Hippocrates is credited with the expression “All diseases begin in the intestines“. With the basic concepts given to him by observation and reflection, the father of medicine anticipated something that has been the subject of numerous scientific investigations in recent years, due to the close relationship between the brain and the gastrointestinal system. Many diseases manifest with digestive symptoms, especially those associated with autoimmune or stressful conditions, such as irritable bowel syndrome or inflammatory bowel disease. Among neurological diseases, degenerative diseases are most associated with gastrointestinal symptoms, which sometimes occur years before the onset of neurological symptoms.

The brain and gut always communicate in two ways. It is common for us to feel stomach and intestinal complaints in stressful situations, which alarm our brain. This digestive symptom, in turn, can amplify the anxiety symptom, becoming a feedback loop.

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The intestines of an adult human are home to trillions of microorganisms (mostly bacteria) with different biochemical properties and genetic material, which makes it the main center of operations for our body. This set of microbes is called the gut microbiota and is unique to each individual. This maintains metabolic balance, produces enzymes, vitamins, short-chain fatty acids (neuroprotective effect), protects the intestines and regulates the release of neurotransmitters. In addition, it plays an important role in regulating the response of the immune system. This microbiota lives in balance with us. It is first obtained during childbirth and breastfeeding. By age 4, it is complete and remains more or less stable throughout adulthood, although it can be affected by factors such as diet, stress, inflammation, and medications.

The digestive tract has its own nervous system that depends on the brain. Microbiota activity generates messages not only about gut motility, but also about what is happening in that interaction with the human body. Communication is always two-way: the microbiota influences human functioning and vice versa.

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When this microbiota-intestine-brain relationship is imbalanced, metabolic disorders, toxin production and reduction of neuroprotective factors occur, which can manifest as cognitive, emotional and appetite disorders. Inflammatory changes alter the immune system and can cause lesions that “trigger” certain neurological diseases such as multiple sclerosis, Parkinson’s or Alzheimer’s disease. The relationship of microbiota with diseases such as cancer, diabetes, obesity, lupus, depression, among others, has been investigated.

A healthy person has a balanced, diverse and resistant microbiota. Stress and a diet rich in ultra-processed foods have been highlighted as responsible for reducing the quantity and quality of gut microbiota and the conditions that result from this change. Then we can conclude that “we are what we eat”. (OR)