Firmicutes/Bacteroidetes (F/B Ratio)

Optimal Result: 12 - 620 Ratio.

The two largest phyla making up the gut microbiome in humans are Firmicutes and Bacteroidetes.

The relationship of these two large groups, expressed as the Firmicutes/Bacteroidetes ratio, has been associated with a number of pathological conditions:

- Obesity has been specifically associated with a greater abundance of Firmicutes and/or a drop in Bacteroidetes (i.e., an increase in the ratio); some research, however, has shown no change or even an increase in Bacteroidetes in obesity

- Disruptions of metabolic homeostasis, e.g., type 2 diabetes and non-alcoholic fatty liver disease

- Elevated markers of inflammation such as IL-6

The Firmicutes/Bacteroidetes Ratio captures the following members of each class:

Total Firmicutes:

- Anaerotruncus colihominis

- Butyrivibrio crossotus

- Clostridium spp.

- Coprococcus eutactus

- Faecalibacterium prausnitzii

- Lactobacillus spp.

- Pseudoflavonifractor spp.

- Roseburia spp.

- Ruminococcus spp.

- Veillonella  spp.

Total Bacteroidetes:

- Bacteroides-Prevotella Group (B. vulgatus & Prevotella spp.)

- Barnesiella spp.

- Odoribacter spp.

Outcomes and General Therapeutic Considerations:

Although no specific therapeutic interventions are yet known for a markedly elevated or depressed Firmicutes/Bacteroidetes Ratio, general intervention strategies directed against some of the commensals may impact this ratio and ultimately gut health.

For imbalances in the F/B Ratio it is best to start by correlating with microbial diversity and abundance, and base treatments on the analytes that are out-of-range.

Age dependent levels:

The Firmicutes/Bacteroidetes ratio undergoes an increase from birth to adulthood and is further altered with advanced age. This ratio appears applicable in highlighting variations between infants, adults and the elderly. It can be linked to overall changes in bacterial profiles at different stages of life. []


- Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population [L]

- The Firmicutes/Bacteroidetes ratio of the human microbiota changes with age [L]

What does it mean if your Firmicutes/Bacteroidetes (F/B Ratio) result is too low?

A high-fiber diet can increase the abundance of Firmicutes and reduce the abundance of Bacteroides and consequently increase the concentration of short-chain fatty acids (SCFAs) in the intestine, inhibiting the development of CRC [Colorectal cancer]. [L]

What does it mean if your Firmicutes/Bacteroidetes (F/B Ratio) result is too high?

- A study has shown that an obese population has a significantly higher level of Firmicutes and lower level of Bacteroidetes compared to normal-weight and lean adults. [L]

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