The Vagus Nerve and the Nervous System Facts

● Neurons are cells found in your brain and central nervous system that tell your body how to behave. There are approximately 100 billion neurons in the human brain [1]●  Your gut contains 500 million neurons, which are connected to your brain through nerves in your nervous system [2]●  The vagus nerve is one of the biggest nerves connecting your gut and brain. It sends signals in both directions [3]For example, in animal studies, stress inhibits the signals sent through the vagus nerve and also causes gastrointestinal problems [4]●  An interesting study in mice found that feeding them a probiotic reduced the amount of stress hormone in their blood. However, when their vagus nerve was cut, the probiotic had no effect [5]●  Interestingly, Vagus Nerve can "taste" sugar in your gut! [6]

Neurotransmitters

● Your gut and brain are also connected through chemicals called neurotransmitters.
● Neurotransmitters produced in the brain control feelings and emotions.
For example, the neurotransmitter serotonin contributes to feelings of happiness and also helps control your body clock [7].
● Interestingly, many of these neurotransmitters are also produced by your gut cells and the trillions of microbes living there. A large proportion of serotonin is produced in the gut [8].● Your gut microbes also produce a neurotransmitter called gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety [9].
● Studies in laboratory mice have shown that certain probiotics can increase the production of GABA and reduce anxiety and depression-like behavior

Gut Microbes Make Other Chemicals That Affect the Brain

● The trillions of microbes that live in your gut also make other chemicals that affect how your brain works [10].● Your gut microbes produce lots of short-chain fatty acids (SCFA) such as butyrate, propionate, and acetate [11].● They make SCFA by digesting fiber. SCFA affects brain function in a number of ways, such as reducing appetite.● One study found that consuming propionate can reduce food intake and reduce the activity in the brain related to rewards from high-energy food [12].● Another SCFA, butyrate, and the microbes that produce it are also important for forming the barrier between the brain and the blood, which is called the blood-brain barrier [13].● Gut microbes also metabolize bile acids and amino acids to produce other chemicals that affect the brain [14].● Bile acids are chemicals made by the liver that are normally involved in absorbing dietary fats. However, they may also affect the brain.● Two studies in mice found that stress and social disorders reduce the production of bile acids by gut bacteria and alter the genes involved in their production [15], [16].

What Foods Help the Gut-Brain Axis?

Here are some of the most important groups for the Gut-Brain Axis:
Omega-3 fats: These fats are found in oily fish and also in high quantities in the human brain. Studies in humans and animals show that omega-3s can increase good bacteria in the gut and reduce the risk of brain disorders [17], [18], [19].Fermented foods: Yogurt, kefir, sauerkraut, and cheese all contain healthy microbes such as lactic acid bacteria. Fermented foods have been shown to alter brain activity [20].High-fiber foods: Whole grains, nuts, seeds, fruits, and vegetables all contain prebiotic fibers that are good for your gut bacteria. Prebiotics can reduce stress hormones in humans [21].Polyphenol-rich foods: Cocoa, green tea, olive oil, and coffee all contain polyphenols, which are plant chemicals that are digested by gut bacteria. Polyphenols increase healthy gut bacteria and may improve cognition [22], [23].Tryptophan-rich foods: Tryptophan is an amino acid that is converted into the neurotransmitter serotonin. Foods that are high in tryptophan include turkey, eggs, and cheese.