Your gut does far more than digest your breakfast, lunch and dinner. It is a busy ecosystem containing trillions of microorganisms, millions of nerve cells and a huge part of your immune system. It also communicates constantly with your brain and can be affected by your diet, sleep, stress, exercise, hormones and even travel.
Some popular facts about the gut are slightly exaggerated, so here are 40 fascinating facts, explained with the science behind them.
20 facts you didn't know about your gut and gut bacteria
Section 1: Your gut is bigger than you think
1. Your gut has a huge surface area
Thanks to folds, tiny projections called villi and even smaller structures called microvilli, your small intestine has an enormous surface area for absorbing nutrients. It’s often quoted that the surface area of your gut is the size of a tennis court. In fact, recent estimates using more accurate measurements suggest it’s more like half the size of a badminton court – but that’s still an awful lot of area to absorb from!
2. You have roughly as many bacterial cells associated with your body as human cells
You may have heard that you have ten times more bacteria than human cells. Modern estimates suggest the numbers are actually much closer to 1:1,. But that still means you carry trillions of bacteria, particularly in your large intestine.
3. Your gut contains a surprisingly large amount of bacteria
Estimates vary, and the old claim that you have exactly 2kg of bacteria is another overestimate. However, most recent estimates suggest the bacteria in your gut weigh at least 200 grams.
4. There can be many hundreds of different bacterial species in your gut
Your microbiome is a complex community. Different people have different combinations of bacteria, and having a wider variety is a good thing. Studies looking at stool samples have revealed more than 3000 species of bacteria living in the gut – although the chances are no one person will ever have all of them.
5. Your gut lining renews itself rapidly
Cells lining your digestive tract are constantly replaced, with much of the intestinal lining renewing within just a few days. What’s more, if the lining of your stomach is injured, new cells migrate in to repair the damage within minutes. This helps protect you from the harsh digestive environment.
6. Your small intestine is around six metres long
The small intestine is called small because of its narrow diameter (the tube is only about 2.5 cm wide), definitely not because of its length! It’s about 6 metres long and this length gives your body plenty of time and surface area to digest food and absorb nutrients.
7. Your microbiome is highly individual
Your gut bacteria are influenced by your genes, diet, lifestyle, environment, age, medications and more. So while your microbiome is influenced by factors you can’t influence, such as your genes, it can vary hugely depending on your diet and lifestyle.
Section 2: The gut-brain connection
8. Your gut has its own nervous system
The enteric nervous system contains millions of nerve cells and controls much of what happens inside your digestive tract. This is why your gut is sometimes called your “second brain”.
9. Most of your body's serotonin is made in the gut
You may have heard of serotonin as the brain’s ‘feel-good’ hormone – but it does much more than that. Around 90% of the body's serotonin is produced outside the brain, mainly by specialised cells (called enterochromaffin cells, just in case you’re interested!) in the digestive tract. Serotonin has many roles in the gut, including helping control movement.
10. Your gut and brain communicate constantly
Signals travel in both directions through nerves, hormones and immune signals. The vagus nerve is one important communication route.
11. Stress can affect your gut microbiome
Anyone who has ever felt under unmanageable levels of stress will recognise that it can affect every aspect of your life. Long-term stress can influence gut movement, secretions and the environment in which bacteria live. Research suggests it can also change both the composition and activity of the microbiome.
12. “Butterflies” in your stomach are real
When you feel nervous or excited, your body produces more adrenaline – the so-called ‘fight or flight’ hormone. This can alter the movement and activity of your digestive system. The strange fluttering feeling is a genuine physical response.
13. Poor sleep can affect your gut
Your sleep-wake cycle and gut microbes interact in a two-way street. Changes in sleep patterns may alter the microbiome, and conversely positive changes to your microbiome may help alleviate sleep problems.
14. Your gut may influence what you want to eat
Gut microbes can interact with the nervous system and produce substances that influence metabolism and appetite. That means that dysbiosis – an imbalance of good bacteria in the microbiome – can contribute to obesity as well as type 2 diabetes, heart disease and stroke.
