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The gut microbiome: balancing the body
The gut microbiome: balancing the body

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2.2 Metabolic – production of nutrients

In addition to digesting the food we eat to provide the human host with nutrients, the gut microbiome also manufactures important micronutrients, such as vitamins and minerals, which are essential to the survival of the human host and other microbiota. For example, the B vitamins are all synthesised by the microbiome. In addition, the microbiota increases absorption of other dietary vitamins and minerals in different parts of the GI tract.

Figure 8 shows some of the dietary micronutrients and SCFAs produced by the microbiome and absorbed across the host gut wall.

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Figure 8 Micronutrients present within the intestinal gut microbiome from the dietary sources and synthesis by the gut microbiome are transported into the intestinal tissue and then into the bloodstream for the host to use
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A schematic illustration depicts micronutrients present within the intestinal gut microbiome and host bloodstream, which support the survival and function of the gut microbiome. The illustration shows a blood vessel (bloodstream), host intestinal tissue lined by intestinal epithelial cells with microvilli, and a microbiome present in the intestinal lumen (inside the tube-like digestive tract. The dietary-derived micronutrients are provided by different regions of the intestine as follows: the duodenum provides vitamins B1, B2, B3, B7, B9, vitamins A, D, E, K, and minerals; the jejunum provides minerals, vitamins A, D, E, K, B vitamins, and vitamin C; the ileum provides selenium, magnesium, vitamins C, D, K, and vitamins B1, B7, B9, and B12; the colon provides vitamins B7, K, potassium, sodium, chloride, and short-chain fatty acids. Micronutrients (inset: fruits, cheese, and vegetables) are also synthesised by the microbiota present in the intestinal lumen. The dietary-derived micronutrients from different regions of the intestines are ultimately absorbed into the intestinal tissue as follows: minerals from duodenum, jejunum, ileum and colon; water-soluble vitamins (vitamins B1 through B12, and C) from duodenum; fat-soluble vitamins (vitamins A, D, E, K) from jejunum; short-chain fatty acids (butyrate, propionate, and acetate) from colon. Micronutrients synthesised from gut microbiota are then transported into the bloodstream.

Figure 8 Micronutrients present within the intestinal gut microbiome from the dietary sources and synthesis by the gut microbiome are ...

Fun fact: why is it called the ‘small’ intestine?

The length of the tube that forms the small intestine is around 6 metres in an adult, compared to the length of the tube forming the large intestine, which is only around 1.5 m in length. So, you might wonder why the small intestine is called ‘small’. The name refers to the diameter of tube, rather than length. The diameter of the small intestine is much smaller than that of the large intestine.

The B vitamins synthesised by the gut microbiome are important in the generation of energy in the cells. Some bacterial groups in the gut microbiome, such as Firmicutes and Bacteroides, synthesise:

  • fat-soluble vitamins such as vitamin A, D, E, and K (around half the daily requirement of vitamin K is provided by gut bacteria)
  • water-soluble vitamins – B vitamins such as folate, thiamine, biotin, riboflavin and pantothenic acid, and vitamin C.

The gut microbiome is an important additional source of the water-soluble vitamins, as levels of these vitamins in food are often inadequate and they cannot be stored in the body.