Everything You Need to Know About Probiotics

Want to know more about probiotics? First you need to understand more about your gut. It’s hard to get your head around the numbers, but your colon (also known as your large intestine) is home to trillions of healthy bacteria, collectively known as the gut flora, or microbiome. In fact, the average person has around 100 trillion microbes in the gut, which is 10 times more than the number of body cells.

For many years it was thought that these microbes were merely residents in the gut with no important function. But recent research shows that this is not the case. Quite the opposite in fact – this complex ecosystem plays an essential role in keeping your body healthy.

Maintaining the balance of the gut flora is emerging as one of the most important things you can do for your well-being (1). The main functions of these “good” gut bacteria are firstly, helping the immune system; secondly, keeping “bad” bacteria at bay; and thirdly, facilitating the absorption of nutrients from food. Gut bacteria are so important that some scientists now refer to them as the “forgotten organ” (2) since any imbalance can lead to the development of a number of diseases.

Immune Function 

A newborn infant does not have any bacterial inhabitants in its gut. But in early infancy – the first few weeks after birth – the gut flora begins to develop through exposure to bacteria through the birth canal. This increase is also facilitated by breast feeding.

Significantly, around 80 percent of your immune system is located in your gut and so ensuring your microbiome is established in early life is very important in staying healthy in later years, as a robust immune system is your defense against harmful pathogens. The “good” bacteria in the gut are involved in fighting “bad” bacteria and by establishing the gut flora in early infancy improves your ability to fight infection. Stress, poor diet and antibiotics can all affect your gut’s delicate balance, making you more susceptible to infection.

Control of Food Absorption

The “good” bacteria in the gut are also very important for the extraction of nutrients from your food during digestion. These good bacteria ferment indigestible carbohydrates (fiber), providing energy from food that would otherwise be unobtainable.

Different bacterial strains and quantity of bacteria in the gut all have an influence on food absorption. In fact, the composition of the gut microbiome has been found to differ between lean and obese individuals. This finding strongly suggests that having the right gut bacteria may contribute to maintaining a healthy body weight.

Interestingly, after a routine medical procedure in the US which involved transferring the microbiome from a healthy individual to one suffering from an antibiotic-resistant gut disease was carried out, the previously lean recipient gained 36 lbs (16 kg). In fact, her body mass index (BMI) increased from 26 to 33 after just 16 months, and 34.5 after three years.

The evidence from both human and animal studies are beginning to stack up, suggesting that there is a link between gut health and body weight. So much so that many US doctors performing fecal transplants no longer use obese people as donors.

Vitamin Synthesis

The gut flora also plays an important role in synthesizing important vitamins, including Vitamin K and several B vitamins (3). Vitamin K is important for normal blood function, including forming clots as well as bone health, while vitamin B is involved in energy and metabolism.

Control of Mood 

The notion that the state of our gut governs our state of mind dates back more than a century, though many dismissed the idea as quackery. Recently, however, new connections between the brain and the gut (the so-called gut-brain axis) have been identified, suggesting there is in fact a very strong relationship between gut health and brain function. It seems that the bacteria in the gut are capable of influencing cravings for particular foods (4).

Furthermore, the gut bacteria have the capacity to influence our behavior and mood through altering signals to the brain. Additionally, the gut is the primary location for storage of your body’s serotonin (5) – the so-called happy hormone – and recent research suggests that synthesis of serotonin is dependent on the microbiome (6). Disruptions to the health of the gut, therefore, may have direct and indirect effects on the health of the brain. Poor gut health has been implicated in several mental health disorders, including anxiety and depression (7).


One of the main contributors to disruption of the natural balance of the gut biome is antibiotics. Of course, antibiotics have very important benefits – killing off potentially harmful, or even life threatening bacteria in your body. But a side effect is that they also kill your healthy gut bacteria (8) This can disrupt the normal functioning of your gut and affect your immune function, the absorption of nutrients and your mood.

Processed Food

Diet plays a major role in defining the composition of the gut too. A recent piece of research from the University of Pittsburgh showed that a typical Western diet, which includes less fiber and more animal protein and fat than that consumed by traditional peoples, could influence the composition of the gut bacteria in just two weeks (9). This works in both negative and positive ways, of course – it means that by changing your diet you can improve your gut health in a relatively short time frame


It’s not only antibiotics and diet which influence the health of your gut flora. Stress lowers the number of protective probiotic bacteria, reducing your immune function and increasing susceptibility to inflammation in your gut (10).

How You Can Change Your Gut Bacteria Balance

So you can see that it’s really important to keep your gut flora healthy. In order to restore the balance, you can make some small changes to increase your overall health and well-being.


Probiotics are supplements which contain living bacteria that colonize your gut, helping to improve the balance of your gut flora. Supplementing with probiotics helps restore the natural balance and diversity of your microbiome. When looking for a supplement, you want at least 2 billion live bacteria per serving. Also, look for well-documented strains with established research benefits and guaranteed delivery to ensure the bacteria reach your gut alive and well.

As probiotics are living organisms, ensure that you take them with a cold drink rather than tea or coffee as the high temperature may kill the beneficial bacteria.

Probiotic bacteria can also found in fermented food and drinks, including yogurt, kefir, sauerkraut, kimchi and miso, which can also work in combination with a probiotic supplement to boost your healthy gut bacteria.


Prebiotics should not to be confused with probiotics. Prebiotics act as food for the probiotic bacteria. Imagine the rich ecosystem of a tropical rainforest; this represents the complexity and diversity of the bacteria in your gut. While the probiotic bacteria act like seeds to increase the number of species, prebiotics in this analogy are the soil providing nutrients that allows the diverse species to thrive.

Prebiotics are commonly known as resistant starch. When we think of starch we often think of starchy carbohydrates such as potatoes, pasta and bread, all of which can spike our blood sugar. However, resistant starch like inulin, as well as that found in beans, lentils and plantains, travels all the way through our digestive system untouched, where our microbiome then breaks it down and uses it for fuel. Bacteria convert it into short chain fatty acids, which help keep these microorganisms healthy. The combination of a probiotic and prebiotic supplement is known as a synbiotic. A synbiotic contains both healthy bacterial strains and prebiotic fiber to help such bacteria thrive.


A final couple of points. As we have already noted, your gut and brain are closely linked, so reducing your stress levels keeps the healthy bacteria your gut in balance. Additionally, exercise can too improve the health of the gut. For example, recent research from University College Cork, Ireland demonstrated that athletes have greater diversity in their gut bacteria than the general population, suggesting that regular exercise improves gut health (11). Another reason to keep moving!


  2. O’Hara, Ann M., and Fergus Shanahan. “The gut flora as a forgotten organ.” EMBO reports 7.7 (2006): 688-693.  
  3. Cummings, J. H., and G. T. Macfarlane. “Collaborative JPEN-Clinical Nutrition Scientific Publications Role of intestinal bacteria in nutrient metabolism.” Journal of Parenteral and Enteral Nutrition 21.6 (1997): 357-365.  
  4. Rezzi, Serge, et al. “Human metabolic phenotypes link directly to specific dietary preferences in healthy individuals.” Journal of proteome research 6.11 (2007): 4469-4477.  
  5. Bornstein, Joel C. “Serotonin in the gut: what does it do?.” Frontiers in neuroscience 6 (2012): 16.  
  6. Yano, Jessica M., et al. “Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis.” Cell 161.2 (2015): 264-276.  
  7. Schmidt, Charles. “Mental health: thinking from the gut.” Nature 518.7540 (2015): S12-S15.  
  8. Pérez-Cobas, Ana Elena, et al. “Gut microbiota disturbance during antibiotic therapy: a multi-omic approach.” Gut 62.11 (2013): 1591-1601.  
  9. http://www.upmc.com/media/NewsReleases/2015/Pages/diet-swap.aspx  
  10. Collins, Stephen M., and Premsyl Bercik. “The relationship between intestinal microbiota and the central nervous system in normal gastrointestinal function and disease.” Gastroenterology 136.6 (2009): 2003-2014.  
  11. Clarke, Siobhan F., et al. “Exercise and associated dietary extremes impact on gut microbial diversity.” Gut (2014): gutjnl-2013.  

This blog was first posted on www.purepharma.com.