The gastrointestinal tract is connected to the brain. Much of the function of the gastrointestinal tract, in digesting our foods and preparing waste for excretion, occurs unconsciously under the control of parts of the brain that we are not consciously monitoring. However, our conscious thought processes and random unthinking food choices can affect proper functioning of the intestinal tract. Our gut works best when the timing of food intake and the amount of food eaten is predictable with a repeated daily rhythm. Unorganized eating, skipping meals, and binge eating large amounts of foods at odd times changes gut function and can lead to common gut-related discomforts including gas, bloating, diarrhea, and constipation.
The process of digestion begins with the visualization of a food and the expected pleasure of eating that food. This visualization can trigger central nervous system activation of gastrointestinal physiology, including secretion of digestive enzymes and hormones in preparation for digestion. Ninety percent of the nerves between the brain and gastrointestinal tract carry messages from the gastrointestinal tract to the brain. The human brain is able to learn and memorize sensory inputs, including those that accompany the consumption of food and drink.
From the taste of foods to their gastrointestinal sensations and social-cultural associations, nutrition takes on many psychological attributes that in many people overtake normal physiology. This can result in strong cravings, and both pleasant and unpleasant feelings related to the consumption of certain foods.
When the stomach is filled with food, signals are sent to the brain reducing hunger. These signals are relatively weak, allowing us to eat large amounts of food until stomach discomfort occurs. We have about 22 feet of small intestine, which digests the food we eat into absorbable sugars, fats, amino acids, vitamins, and minerals. Nervous system signals control the process of digestion as the food is moved along by rhythmic contractions of the muscle in the intestinal walls.
Fear and anxiety can lead to diarrhea in some people and constipation in others. Gas pains result when the walls of the intestines are stretched by gases released from foods during digestion or from swallowed air. The gases from foods are produced by the bacteria in the gut known collectively as the microbiota or microbiome. When you eat foods, the substances that are not digested in your small intestine pass into the colon or large intestine. There are trillions of bacteria in over a thousand different species that work to digest what is passed into the colon. There are many beneficial substances produced by these bacteria that maintain gut health and some that go into the blood stream and are detected by the brain.
A particular short-chain fatty acid produced by the bacteria in the colon is propionic acid. This fatty acid has been shown to affect food intake at the appetite centers in the brain in some studies (1). On the other hand, complex sugars found in some vegetables, such as broccoli, can lead to excess gas production and discomfort. The foods you eat affect the types of bacteria growing in the colon. The brain’s effects on the movement of the colon can also affect the movement and growth of these bacteria.
The conditions of diarrhea, constipation, and gas pains affect many people and account for the many remedies being sold for these conditions. Balanced nutrition and exercise with adequate fiber will help the digestive system function normally. Adequate sleep, relaxation, and stress reduction can help keep your gut-brain connection functioning normally.
1. Chambers ES, Viardot A, Psichas A, Morrison DJ, Murphy KG, Zac-Varghese SE, MacDougall K, Preston T, Tedford C, Finlayson GS, Blundell JE, Bell JD, Thomas EL, Mt-Isa S, Ashby D, Gibson GR, Kolida S, Dhillo WS, Bloom SR, Morley W, Clegg S, Frost G. Effects of targeted delivery of propionate to the human colon on appetite regulation, body weight maintenance and adiposity in overweight adults. Gut. 2015 Nov;64(11):1744-54.