Gut Brain Axis
What is the gut brain axis?
This two-way communication network connects the digestive system and the brain.
True or false: Approximately 300 million people worldwide are affected by major depressive disorder.
True
What is chronic (low-grade) inflammation?
This type of inflammation — not the short-term healing kind — is associated with depression and many other chronic health conditions.
Approximately what percentage of the body's serotonin is produced in the gut?
90-95%
According to Prof. Tim Spector's ZOE video, this is the number of different plants he recommends eating each week for gut health.
30
What is the vagus nerve?
This major nerve is one of the key communication highways between the gut and the brain.
What is dysbiosis?
This general term describes an alteration or imbalance in the gut microbial community.
What types of food can cause gut inflammation?
- Ultra-processed foods: Additives, artificial colors, and preservatives can provoke the gut barrier.
- Sugar and refined carbs: Excess sugar feeds harmful bacteria, which promotes inflammation.
- Unhealthy fats: Diets high in saturated and trans fats can deteriorate the gut barrier
What is tryptophan?
This amino acid is the raw material (precursor) that gut cells use to make serotonin.
What are polyphenols?
These are colorful plant compounds, found in foods like berries, kale, olive oil, and dark chocolate, are one of the five things ZOE recommends for gut health.
The gut has its own nervous system — the enteric nervous system - how many millions of nerves?
A) 100 million
B) 200 million
C) 500 million
C - 500 million
What skin conditions can be caused by poor gut health?
Eczema, Psoriasis, Acne
Name a herb/spice that has anti-inflammatory properties?
Turmeric, Ginger, Cinnamon, Garlic
What is the blood-brain barrier? (Gut serotonin cannot readily cross it; brain serotonin is made separately.)
Although most serotonin is made in the gut, it does NOT directly control mood in the brain because of this biological barrier.
Name the FIVE things Prof. Tim Spector recommends in the ZOE video for better gut health.
(1) eat ~30 different plants per week, (2) eat polyphenol-rich/colorful foods, (3) increase fiber, (4) eat fermented foods, (5) reduce ultra-processed foods
What is leaky gut?
When the gut barrier becomes "leaky," this bacterial product can enter the bloodstream and trigger an immune response linked to depression.
True or False? Bananas contain a modest amount of the essential amino acid tryptophan, which your body and gut microbes help convert into serotonin to support the gut-brain axis.
True
Approximately what percentage of people with major depressive disorder may have inflammatory markers within the normal range, suggesting inflammation is not a universal cause.
A) 30%
B) 40%
C) 65%
Around 40%
Explain why the statement "95% of serotonin is in the gut, so gut bacteria directly control your happiness" is an oversimplification.
Gut serotonin acts locally and cannot readily cross the blood-brain barrier; brain serotonin is produced separately by neurons; gut serotonin may influence mood only indirectly through the vagus nerve.
ZOE recommends replacing ultra-processed snacks with healthier alternatives. Name THREE examples of snacks Prof. Spector suggests instead.
olives, popcorn, nuts, seeds, peanut butter, hummus with vegetables, berries
The gut-brain axis is described as "bidirectional" — name TWO directions of influence (i.e., two ways the relationship works).
The gut influencing the brain (e.g. via microbes, metabolites, vagus nerve) AND the brain/lifestyle influencing the gut (e.g. stress, poor sleep, medications altering gut microbes)
True or False, and explain: "A specific gut bacterium has been proven to directly cause depression in humans."
FALSE - The microbiome is a plausible and bidirectional contributor, but no single bacterium has been proven to directly cause depression in humans.
True or false: the animo acid trytophan is needed to make serotonin in the brain.
True: People with major depression often show lower levels of plasma tryptophan, which is the essential amino acid needed to make serotonin in the brain
How does gut-derived (peripheral) serotonin primarily communicate with or influence the central nervous system along the gut-brain axis?
Activation of the vagus nerve
Prof. Spector recommends fermented foods for gut health. Name FOUR examples of fermented foods he mentions AND explain why they are beneficial.
yogurt, kefir, kombucha, kimchi, sauerkraut — because they contain live microbes that may support microbiome diversity and reduce inflammation