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Discover the role of good and bad bacteria in the GI tract, or gut.

Key points

  • Beneficial flora help us digest and absorb food and produce chemicals that kill viruses, bad bacteria and fungi.
  • Opportunistic flora, also known as 'bad bacteria', can cause disease when they are not managed.
  • Transitional flora are the bacteria in food and drink. If the GI tract is healthy, they pass through without causing any harm.

The GI tract is also known as the gut. Trillions of bacteria and tiny organisms, called flora, live there.

Three main types of flora live in the gut:

  • beneficial flora
  • opportunistic flora
  • transitional flora.

Our age, health and diet affect the amount and type of flora in each part of the gut.

Beneficial flora

As their name suggests, beneficial flora are "good bacteria". They help us digest food and keep our gut healthy. Two major types of beneficial flora are Lactobacillus acidophilus (lactobacteria) and Bifidobacterium bifidum (bifidobacteria).

Opportunistic flora

These flora are more commonly known as "bad bacteria". They normally live in the gut, but if they are not managed, they will find any opportunity to cause disease. Examples of opportunistic flora include streptococci and yeast.

Transitional flora

These are the bacteria found in everything we eat and drink. They pass through our GI tract along with the food. When the tract is healthy, the transitional flora pass through without causing any harm. However, if the intestines are weak or damaged, the transitional flora can cause disease.

The role of flora in digestion

Beneficial flora help us digest and absorb the food we eat. They produce enzymes that help break down carbohydrates. Once broken down in the intestines, nutrients need to pass through the gut wall into the blood. The beneficial flora help with this process so the vitamins and minerals can travel to other tissues in the body.

One form of good bacteria, lactobacteria, live in the small intestine. They help us digest dairy products and lactose, the sugar found in milk. The other major type of good bacteria, bifidobacteria, live in the colon. Among other things, they produce B vitamins, regulate bowel movements and produce antibiotics to kill bad bacteria.

Some foods contain beneficial flora and natural enzymes that help our intestines break down food. However, many processed foods do not contain any helpful flora or enzymes.

The role of flora in our immune system

When we breathe, we draw in many substances. These range from harmful bacteria, moulds and viruses to simple particles such as dust and hair. The food we eat also contains good and bad substances. Cooking kills most bacteria, but some still linger and harm the food afterwards.

The immune system protects us from these constant threats. It is most active in the small intestine. In fact, about 80 per cent of our immune system's activity is in the intestines.

In a healthy person, there is enough acid in the stomach to kill most harmful substances. In less healthy people, the substances reach the small intestine or colon.

In healthy people, beneficial flora in the small intestine produce useful chemicals that kill viruses, bacteria and fungi. These chemicals also help create an environment in the intestine that makes is hard for bad bacteria to survive.

Factors that can damage beneficial flora

If beneficial flora are damaged, the gut becomes vulnerable to substances that could lead to infections.

Some common ways we can damage or decrease beneficial flora in our intestines include taking certain medicines regularly and eating food lacking in nutrients.

In terms of medicines, antibiotics are known to kill bad bacteria and the infections they cause. However, they can also kill the good bacteria, or beneficial flora. When this happens, yeast or bad bacteria start to grow in their place.

If beneficial flora are damaged, it can take them weeks to months to fully re-establish themselves inside the gut. Eating a range of nutritious food from the food groups in Canada's Food Guide can help keep our beneficial flora healthy.

Last updated: September 27th 2013