Most of us take our digestion for granted, and yet it is an incredibly sophisticated system that allows our bodies to extract energy and nutrients from everything we eat and drink.
Digestion involves many different organs – from the brain to the liver via the stomach and intestines – and a complex interplay between them to ensure enzymes and acids are secreted in just the right quantities, at just the right time; that the passage of food through the gut happens neither too quickly nor too slowly; and that regular bowel movements occur to remove waste from the body in a timely fashion.
When the system is working optimally then digestive symptoms such as bloating, flatulence and abdominal pain are rarely experienced. It is often the appearance of such symptoms that is the first indication that an individual’s digestion may need a helping hand.
Let’s take a closer look at how digestion works and the role bacteria and probiotics play in maintaining a healthy digestive system.
How does digestion work?
Digestion starts as soon as the brain registers that food is about to be consumed. Known as the cephalic phase, the smells and sight of a meal trigger the release of digestive enzymes and stomach acid which are critical for the initial breakdown of food. Your mouth watering in anticipation of eating is exactly this – the saliva being produced contains digestive enzymes that start to digest the carbohydrates in your meal as soon as the first bite is taken. The process of chewing also serves to physically break down the food you are eating and mix it with saliva.
Once food has reached the stomach it is mixed thoroughly with hydrochloric acid which starts the digestion of protein. From here the food, now a semi-liquid substance known as chyme, passes into the small intestine. More digestive enzymes and bile acids are released that work on carbohydrates, fats and protein to break them down further, and the absorption of nutrients starts to take place.
On entering the large intestine, or colon, the majority of carbohydrates and protein have been fully digested and absorbed. The exception to this is any fiber that the body is unable to digest, namely insoluble fiber and/or cellulose from plant foods. This undigested prebiotic fiber provides food for our gut bacteria, the majority of which reside in the large intestine.
What role do our gut bacteria play in digestion?
Once the remains of a meal or snack reach the large intestine, gut bacteria – of which there are thought to be ten times the number of human cells – help ferment any undigested dietary fiber, producing short chain fatty acids (SCFAs) that in turn provide a source of energy.
They also digest polyphenols, plant micronutrients with bright colours and anti-oxidant properties; breaking them down so that they can be absorbed and utilized within the body.
Other ways in which gut bacteria are thought to support digestion include:
- regulating gut motility, the speed at which food travels through the digestive tract
- promoting absorption of minerals
- producing enzymes such as beta-galactosidase, to aid digestion of lactose
- synthesizing certain vitamins, such as vitamin K
- improving the function and integrity of the gut barrier to ensure that large food particles do not cross into the bloodstream
Can gut bacteria negatively affect digestion?
When the microbiome is healthy and balanced, with beneficial gut bacteria outnumbering the ‘bad’ or pathogenic bacteria, the positive effects on digestion noted above may be seen. However, if this balance is tipped in favor of the potentially pathogenic bacteria strains, an imbalance occurs, known as dysbiosis.
When this happens, unwanted digestive symptoms such as bloating, gas, indigestion, constipation and diarrhea (frequently grouped together and given a label of irritable bowel syndrome) are commonly experienced.
In what way can probiotics benefit digestion?
Probiotic supplements can help to promote a balanced microbiome, with ‘good’ probiotic bacteria crowding out the pathogenic strains and preventing them from overgrowing. This will promote the beneficial effects of gut bacteria listed above, while reducing unwanted symptoms, such as dysbiosis.
In addition to effects on motility, absorption and prebiotic fiber digestion, a number of studies have shown that probiotic bacteria in yogurt can also help to ease unwanted digestive symptoms such as abdominal cramps, diarrhea, vomiting, bloating and flatulence in those with lactose sensitivity.
Although they can support our existing gut bacteria, probiotic supplements do not colonize the intestine. They are known to offer a transitory effect on gut health, with benefits thought to last for approximately 72 hours, at which point the probiotic bacteria will have passed through the digestive tract. It is for this reason that long-term use of probiotic supplements may confer greater benefits.
When choosing probiotics to support digestion, it is important to look for a research-backed multi-strain supplement that contains high numbers of bacterial strains that are naturally present in the human gut.