Digestion

What are the bacteria that help with human digestion?

Bacteria that live in the gut and are a part of the intestinal flora are often not considered an important constituent of the digestive process. However, the role of bacteria in digestion is an important one. These microbes help in breaking down food and produce enzymes which help in digesting food. These enzymes are otherwise not produced by the body.

There are about 300 to 1000 different species of bacteria that reside in the gut. Fungi and protozoa also known to be present. But their role in digestion is yet to be identified. There are hundreds of different genes of bacteria present in the digestive tract. The genera of bacteria that is mostly found in the gut are Bacteroides, Fusobacterium, Clostridium, Ruminococcus, Eubacterium, Peptostreptococcus, Peptococcus and Bifidobacterium. The genera Escherichia and Lactobacillus are found to a lesser extent. About 30% of the bacteria in the gut belong to the species Bacteriodes. The latter is one of the most important bacteria needed for the healthy functioning of the body.

It is extremely important to maintain the intestinal flora balance of the gut to ensure that food is properly digested and the nutrients are efficiently assimilated.

Certain bacteria like the Lactic acid bacteria (LAB) and the Bifidobacteria can be obtained from external food sources. These food sources are referred to as probiotics. These bacteria are obtained from fermented foods with added live cultures like yogurt, bread made from sour dough etc.

What are the different functions of bacteria in digestion?

The different functions of bacteria in the normal functioning of the body are as follows:

1. Fermentation and metabolism of carbohydrates:

  • Human cells lack certain enzymes required for breaking down certain carbohydrate molecules known as polysaccharides. The type of carbohydrates that require the enzymes produced by these microbes to be digested are starches, fiber, oligosachharides (found in beans) and sugars. As a result, intestinal gas is formed from undigested carbohydrates of the specified type and flatulence is experienced.
  • The carbohydrates are fermented with the aid of the bacteria and are converted into short chain fatty acids (SCFA) s. This type of fermentation is known as Saccharolytic fermentation. The byproducts of this molecular transformation are acids such as acetic acid, propionic acid and butyric acid. These acids provide nutrition by enabling the body to absorb essential minerals in diet such as iron, calcium and magnesium. These organic acids also help to provide energy to the body by helping the liver produce ATP (Adenotriphosphate) to be used up by the muscles.
  • Butyric acid supplies energy to the cells of the digestive tract. It may also help prevent the abnormal mutations (cell division) in cells causing cancer.
  • Bacteria affects metabolism of carbohydrates and affects the storage and absorption of fats. It is an important factor affecting obesity.
  • They enable the absorption of Vitamin K in the body in the process of metabolizing carbohydrates.
  • They enable the gut to absorb more water. In fact, 60% of the dry mass of stools is made up of these bacteria.

2. Effect on the cells of the gastrointestinal tract:

They help in the growth of the epithelial cells present on the intestinal surface. They can help alter the cell structure in the mucus lining of the digestive tract and prevent an injury from occurring.

Colony of Escherichia coli

Electron micrograph image of Helicobacter Pylori

3. Destroying the harmful bacteria of the gut:

  • Certain bacterial species like clostridium difficile, helicobacter pylori are harmful to the digestive tract and can cause severe diarrhea, ulcers and even gastric cancer. The gut friendly bacteria protects the digestive tract from the harmful bacteria by creating a “barrier effect”. The good bacteria sticks to the mucus lining preventing the harmful microbes to pass through.
  • The gut flora also produces bacteriocins, which are toxic proteins that inhibit the colonization of harmful microbes.
  • The fermentation of food brought about by the good bacteria produces certain fatty acids like the lactic acid. The latter reduces the pH balance in the colon. This helps to thwart the multiplication of the harmful bacteria and can also help discharge certain carcinogens.

4. Enhancing Immunity:

  • These bacterial reactions have a continuous effect on the immune system. The mucosal membranous layer of the digestive tract is a protective mechanism of the immune system.
  • They stimulate the cells in the lymph nodes associated with the gastric mucosa and cause it to produce antibodies to fight the pathogenic microbes.
  • The immune system is trained over time to single out the harmful bacteria and let the antibodies act on it.
  • Bacteria induces oral tolerance which makes the immune system less reactive to pathogens. This is especially useful in auto immune diseases and in case of allergies.

5. Helps to metabolize proteins:

It helps to metabolize and discharge dietary carcinogens (cancer causing). Heterocyclic Amine (HCA) is a substance which is obtained from the metabolization of proteins and could be a carcinogenic microcomponent. The gut flora fights such substances and prevents them from inducing malignant tumors.

6. Helps to prevent allergy:

As discussed earlier, the gut flora helps to train and strengthen the immune system. The immune system is trained to identify pathogens and fight them. Allergies are caused by a hypersensitive immune system when it starts to treat otherwise harmless proteins and irritants in food and the environment as threats and produces antibodies to fight them. Studies have shown that those who have allergies or may get them later on, have a different composition of intestinal flora as compared to those who do not have allergies.

7. Helps to prevent Inflammatory Bowel Disease:

Increasingly, studies indicate that by improving gut health, gut friendly bacteria can help prevent inflammation of the colon as in Crohn’s disease and other inflammatory bowel diseases. The carbohydrates when broken down into short chain fatty acids (SCFA)s help to prevent any inflammatory condition of the large intestine.

The above points help to illustrate the beneficial role of

bacteria in digestion

. In this context,it is important to explain that taking antibiotics to fight any existing infection caused by harmful bacteria can cause damage to the beneficial bacteria and upset the flora balance. Antibiotics can cause “Antibiotics Associated Diarrhea” by allowing the proliferation of the pathogenic bacteria causing destruction of the good bacteria.

How not to endanger the gut friendly bacteria?

  • The only way of protecting the good bacteria of the gut is to eat organic food especially meat. Cattle and poultry are often injected with a lot of antibiotics. So unknowingly we end up consuming a lot of antibiotics while intaking meat. Eating organic food will help avoid these unnecessary antibiotics.
  • Probiotic supplements and foods like yogurt and buttermilk will help restore the good bacteria in the gut.
  • Try not to overwhelm the intestinal flora with foods having very high fat content or sugar content. Minimise sugar and starches, as these are conducive for the growth of the pathogenic microbes.
  • Try eating raw and minimally processed food. The chemicals and additives in processed food kill beneficial bacteria.
  • Foods that promote the growth of intestinal flora should be taken. Fiber rich food is essential to maintain a healthy balance of the gut flora. A particular fiber, namely, inulin cannot be broken down in the small intestine and reaches the large intestine almost intact. This is especially beneficial for the colon. Bananas, peas, asparagus, different baby greens, garlic, almonds, artichokes and onions all have inulin. Eating fiber supplements based on psyllium husk can also improve digestion.

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