The digestive system is a group of organs that work together to change the food you eat into the energy and nutrients your body needs. After you consume food and liquids, the digestive system breaks them down into their basic parts: carbohydrates, proteins, fats, and vitamins. These basic nutrients are then absorbed into the bloodstream, which carries them to cells throughout the body. Nutrients provide the cells with the energy they need for growth and repair. Everything in your body, from your hormones to your heart, needs the nutrients from the digestive process to work correctly.1
Your body is full of trillions of bacteria, viruses and fungi. They are collectively known as the microbiome.
While some bacteria are associated with disease, others are actually extremely important for your immune system, heart, weight and many other aspects of health.
In fact, there are more bacterial cells in your body than human cells. There are roughly 40 trillion bacterial cells in your body and only 30 trillion human cells. That means you are more bacteria than human.2
Altogether, these microbes may weigh as much as 2–5 pounds (1–2 kg), which is roughly the weight of your brain. Together, they function as an extra organ in your body and play a huge role in your health.
The key to a healthy microbiome is nourishing a balance among the nearly 1,000 different species of bacteria in your gut.
There are two ways to maintain this balance — helping the microbes already there to grow by giving them the foods they like (prebiotic) and adding living microbes directly to your system (probiotic).3
Prebiotics are a type of fibre that the human body cannot digest. They serve as food for probiotics, which are tiny living microorganisms, including bacteria and yeast. Both prebiotics and probiotics may support helpful bacteria and other organisms in the gut.
Prebiotics and probiotics both support the body in building and maintaining a healthy colony of bacteria and other microorganisms, which supports the gut and aids digestion.
These food components help promote beneficial bacteria by providing food and creating an environment where microorganisms can flourish.
Prebiotics are present in fibre-rich foods, such as fruits, vegetables, and whole grains. Probiotics occur in many fermented foods, including yogurt, sauerkraut, and tempeh.4
Probiotic foods
Many foods are rich in probiotics, including:
- yogurt
- kefir
- fermented foods, such as sauerkraut and kimchi
- kombucha
- traditional fermented buttermilk
- fermented cheeses, such as Gouda
Prebiotics are in many high-fibre foods, including some fruits, vegetables, and whole grains.
Some probiotic-rich foods may also contain prebiotics.
Babies get access to prebiotics through the sugars in breast milk, and some infant formulas also contain prebiotics.
As your microbiome grows, it affects your body in a number of ways
Digesting breast milk: Some of the bacteria that first begin to grow inside babies’ intestines are called Bifidobacteria. They digest the healthy sugars in breast milk that are important for growth.
Digesting fibre: Certain bacteria digest fibre, producing short-chain fatty acids, which are important for gut health. Fibre may help prevent weight gain, diabetes, heart disease and the risk of cancer.
Helping control your immune system: The gut microbiome also controls how your immune system works. By communicating with immune cells, the gut microbiome can control how your body responds to infection5
Helping control brain health: New research suggests that the gut microbiome may also affect the central nervous system, which controls brain function. First, certain species of bacteria can help produce chemicals in the brain called neurotransmitters. For example, serotonin is an antidepressant neurotransmitter that’s mostly made in the gut. Second, the gut is physically connected to the brain through millions of nerves.6 Therefore, the gut microbiome may also affect brain health by helping control the messages that are sent to the brain through these nerves
Helping control your weight: Gut dysbiosis may lead to weight gain, but probiotics can potentially restore gut health and help reduce weight.7
Helping control heart health: Interestingly, the gut microbiome may even affect heart health. A recent study shows that in 1,500 people found that the gut microbiome played an important role in promoting “good” HDL cholesterol and triglycerides.
How Can You Improve Your Gut Microbiome?
There are many ways to improve your gut microbiome, including:
Eat a diverse range of foods: This can lead to a diverse microbiome, which is an indicator of good gut health. In particular, legumes, beans and fruit contain lots of fibre and can promote the growth of healthy Bifidobacteria
Eat fermented foods: Fermented foods such as yogurt, sauerkraut and kefir all contain healthy bacteria, mainly Lactobacilli, and can reduce the amount of disease-causing species in the gut.
Limit your intake of artificial sweeteners: Some evidence has shown that sweeteners like aspartame increase blood sugar by stimulating the growth of unhealthy bacteria like Enterobacteriaceae in the gut microbiome.
Eat prebiotic foods: Prebiotics are a type of fibre that stimulates the growth of healthy bacteria. Prebiotic-rich foods include artichokes, bananas, asparagus, oats and apples.
Breastfeed for at least six months: Breastfeeding is very important for the development of the gut microbiome. Children who are breastfed for at least six months have more beneficial Bifidobacteria than those who are bottle-fed.
Eat whole grains: Whole grains contain lots of fibre and beneficial carbs like beta-glucan, which are digested by gut bacteria to benefit weight, cancer risk, diabetes and other disorders.
Try a plant-based diet: Vegetarian diets may help reduce levels of disease-causing bacteria such as E. coli, as well as inflammation and cholesterol.
Eat foods rich in polyphenols: Polyphenols are plant compounds found in red wine, green tea, dark chocolate, olive oil and whole grains. They are broken down by the microbiome to stimulate healthy bacterial growth.
Take a probiotic supplement: Probiotics are live bacteria that can help restore the gut to a healthy state after dysbiosis. They do this by “reseeding” it with healthy microbes.
Take antibiotics only when necessary: Antibiotics kill many bad and good bacteria in the gut microbiome, possibly contributing to weight gain and antibiotic resistance.
1 Your Digestive System & How it Works
2 Revised Estimates for the Number of Human and Bacteria Cells in the Body
3 How Probiotics Can Help You Lose Weight and Belly Fat
4 Rountree R. The human microbiome — Humans as super-organisms. Alternative and Complementary Therapies. 2011
5 Dietary fiber and weight regulation
6 From Dietary Fiber to Host Physiology
7 Relationships Among the Brain, the Digestive System, and Eating Behavior