Microbiome Diversity and Firmicutes/Bacteroidetes Ratio

Within our gut, particularly in the large intestine, lies trillions and trillions of different microorganisms, but mainly bacteria – and this is a good thing. Without these gut microbes, important functions that support immune health and brain development could be seriously impaired.

Our gut microbiome plays a crucial role in helping to break down and ferment dietary fibre, helping to produce health-boosting molecules called short chain fatty acids. These microbes also help to produce some B vitamins and vitamin K, for both us and gut bacteria to use. And not only this, our gut microbiome also helps to guard us from harmful pathogens in our environment, while also supporting cognitive function, our mental health and can even help us to lose weight. 

The diversity of the gut microbiome

The ‘diversity’ of the gut microbiome is often used as an indicator of good health. This refers to the variety of different beneficial species that live in our gut, as well as the abundance of each of these species. It has been shown that those who have the most diverse gut microbiomes may have more efficient immune system responses, better metabolic health, less risk of developing allergies later in life, and less risk of developing obesity. 

How is diversity measured in the gut? 

When it comes to measuring diversity in the gut, there are a few different ways that scientists do this.  Two metrics in particular are the Shannon Index and the Simpson Index: The Shannon Index looks at both the ‘richness’ and ‘evenness’ of species in a community, and when a score is calculated from a sample, we see that a higher index score indicates greater diversity. The Simpson Index also can help us work out the diversity of the gut, and is a measure of dominance of a species within it. 

While these measures show us how diverse the gut microbiome is, researchers are also interested in looking at which types of bacteria are most abundant, as well as the balance between them. We call these bacteria groups “phyla”, and the most common ones found within our gut are Firmicutes and Bacteroidetes – making up almost 90% of the bacterial population there. 

The balance between Bacteroidetes and Firmicutes

Researchers have become particularly interested in the balance between Bacteroidetes and Firmicutes in recent years, as it has shown to be an indicator of obesity, some inflammatory disorders, and the overall health of the gut. We know that not only things like fibre intake can affect this ratio, but also our age too: as we get older, the ratio can increase putting us at risk of more health issues over time. This is why it is important to continue to focus on improving diet quality throughout our lifespan.  

The F/B ratio and obesity:

Although obesity is influenced by many factors like diet quality, energy intake, and genetics, some studies have reported that individuals with obesity may have a higher F/B ratio in their gut microbiome too. In one study, obese participants were put on a calorie deficit diet for one year. They saw a shift towards a more balanced F/B ratio, in parallel with their weight loss. Another study on Ukrainian individuals showed that as BMI increased, the proportion of Firmicutes relative to Bacteroidetes in the gut microbiome also increased. And in one animal study, it was seen that obese mice had a higher ratio of Firmicutes to Bacteroidetes, while lean mice had a lower ratio. Researchers then saw that when other mice received gut bacteria from the obese mice, their body fat increased by around 47%, whereas mice receiving the bacteria from lean mice only saw a 27% increase in body fat. So, research is still developing in this area, but what we do know is that having a healthy balanced diet and eating fermented foods that contain probiotics can create shifts in the gut microbiome that favour a more balanced F/B ratio, which may help reduce the risk of developing obesity. 

Inflammatory disorders and the F/B ratio:

It has been seen that some conditions, like Type 2 diabetes and Covid 19 may be associated with higher F/B ratios compared to healthy individuals. A healthy ratio helps to maintain normal homeostasis within our gut, so when this is out of balance it can boost markers of inflammation. Some species of Firmicutes are particularly good at being able to break down complex sugars and fats from our diet, boosting their availability to be absorbed and therefore leading to the body absorbing more calories. This not only can contribute to increased risk of developing obesity, a condition we discussed above, but it may also be associated with increased inflammation associated with developing type 2 diabetes. 

The F/B ratio and gut health disorders:

An increase in Bacteroidetes and decrease in Firmicutes has been linked with inflammation in the bowel. This imbalanced ratio can contribute to conditions like Irritable Bowel Diseases including Crohn’s or Ulcerative Colitis. This was demonstrated particularly well in two different studies looking at biopsies of the human gut. Biopsies were taken from inflamed and non-inflamed regions of the guts of IBD sufferers as well as healthy individuals, and it was shown that a reduced number of Firmicutes and increased number of Bacteroidetes were seen in the IBD samples. This imbalanced ratio has also been seen in stool samples, where in one study it was seen that those suffering with Crohn’s disease had much higher levels of a type of Bacteroidetes compared to healthy individuals. 

How can you restore balance in the gut?

After seeing the impact an imbalanced gut can have on our health, you may now be wondering how we can restore a healthier balance. This can be done in a number of ways through diet and lifestyle improvements.

Exercise

Firstly, exercise has been shown to potentially increase the ratio between Bacteroidetes to Firmicutes, which may favour weight loss and a reduction in obesity risk. Regular movement, especially outdoors can also support digestion and reduce constipation – a condition that can lead to inflammation in the gut.

Probiotics

Probiotics have also been used in some studies to help rebalance the F/B ratio. However, the specific strain of bacteria in the probiotic is important. Eating more plant foods containing fibre can also reduce the risk of gut dysbiosis, while also helping to feed the existing beneficial gut bacteria, allowing it to thrive and support our health.

Fermented foods

And lastly, enjoying more fermented foods like greek yoghurt or Biotiful Kefir products (especially those containing Lactobacillus) has been shown to help decrease the F/B ratio, reducing obesity in several animal studies.