The gut conundrum

02 Apr 2019

Allison Cartwright was determinded to discover potential reasons behind being 'overweight'. As part of her enquiries, she had some of her gut microbes identified. What did she learn? 

Diet and weight are an obsession in my family. After being classified as obese since the age of 2, I’ve tried more diets than I can count.

Regardless of nutritional efforts, obesity is a categorisation I’ve yet to escape. I do more exercise than any of my friends and eat healthier food. My diet is far from perfect, but I’ve always thought my weight was unfair.



Genetic disposition


I try and console myself with excuses. Option 1: it’s my genes. Looking at my family, there’s a mix of weights, but I certainly fall on the heavier end.


My Mom always refers to her mother as a 5 ft barrel as broad as she was high, so it was convenient to blame my gran’s gene. A birthday gift of a genetic testing kit brought no comfort [1]. My genes showed I should have ‘an average weight’. Damn! My familiar excuse could not cut it anymore.   


There was no hope but to turn to Option 2. I’m very muscular and it’s often said that muscle weighs more than fat. Sadly, this isn’t true, as they weigh the same, but muscle takes up less space due to it higher density [2].


An addiction to sports has led to a muscular frame, so I probably look slimmer than my body mass portrays. The results of my gene testing kit said my muscle composition was ‘common in elite athletes’. Phew! An explanation for my muscular composition, but what about the additional fat?


As a microbiologist, it's interesting to hear that the gut microbiome can affect health, and possibly weight.



Gut instinct


Could microbes be to blame for the retention of those extra pounds? There was an option to learn more; send a faecal sample for analysis as part of the British Gut project [3].


My Mom agreed to send one too. As our diets are very similar, it would be interesting to compare results.


Before sending the sample, we completed participant surveys. These showed our main differences would be age (Mom is 27 years older), swimming pool exposure (Mom swims twice a week, I swim 4 times), time spent living in Africa (I left Zimbabwe aged 11, Mom was 38) and a difference in our breakfast diet (I eat whole grain cereals while Mom usually has eggs).


My mom also has IBS which was attributed by a doctor to a sudden radical change in her diet when she joined Slimming World in 2010. Survey completed, we sent our samples and awaited the sequencing and identification of our gut microbiome.


When the results arrived, they showed that 55% of my gut bacteria were from the Firmicutes phyla and 40% was from the Bacteroidetes phyla. In comparison, my Mom’s gut was dominated by the phyla Proteobacteria, accounting for 50% with Firmicutes and Bacteroidetes comprising 25% and 20% respectively. Despite the similarity of our diet, we have very different gut microbiomes.


Further exploration of our results showed my gut’s abundance in the genus’s Bacteroides (phyla Bacteroidetes) and Faecalibacterium (phyla Firmicutes), and the family Ruminococcaceae (phyla Firmicutes).



Family business


My Mom’s gut was abundant in the genus’s Enterobacter (phyla Proteobacteria) and Bacteroides, and the family Ruminococcaceae and so it looks like our microbiome have similar common microbes. The main difference in our samples were the abundance of Faecalibacterium in my gut which were replaced by Enterobacter in my Mom’s gut. Presented with the above info, does it mean we have a healthy gut microbiome?


Some of the microbes found in our gut have been linked to weight loss and good health. These  include Ruminococcaceae and Faecalibacterium. Ruminococcaceae, abundant in both our guts has been associated to protect against weight gains [4] and so this can’t be linked to my higher weight.


Faecalibacterium, common in my gut could be helping to boost my immune system as the only known species Faecalibacterium prausnitzii produces the molecule butyrate which protects against microbiological invasive and slows the spread of cancerous cell division [5]. Regardless of whether it affects my weight, Faecalibacterium seems a beneficial inhabitant.


The results also included a list of the most enriched microbes, which in my gut comprised a 9-fold enrichment of the genus Victivallis and a 2-fold enrichment of the genus Oscillospira, which are both beneficial.


Victivallis includes Victivallis vadensis that breaks down cellobiose a sugar from plants probably enriched as I eat a lot of fruit and veg showing that my microbiome reflects my diet [6]. Oscillospira is used to process animal-derived sugars in diets rich in animal products and associated with leanness and health [7, 8] so again I am glad to have these bacteria.



Bacterial blame


Both of our guts had enriched levels of Bacteroides, but it is unclear whether this is good. Bacteroides has been associated with diets high in wholegrains and can reduce the risk of cardiovascular disease and strokes through slimmer waistlines, higher amounts of high-density lipoproteins which reduce atherosclerosis, and lower blood pressures [9, 10].


However, other studies have shown that higher Bacteroides are linked to weight gain if they are more abundant than Firmicutes, and higher abundances of Bacteroides can lead to excessive weight gain during pregnancy so it’s a good thing I don’t want children [11, 12]. The conflicting studies could reflect the wide diversity of microbes in the genus but this leaves me unsure whether to blame high Bacteroides level for my obesity?


So far, all the microbes in our guts have been linked to some beneficial properties, but some of the bacteria in my Mom’s gut are linked to poorer gut health including her Enterobacter and her 2-fold enrichment in the family Enterobacteriaceae. Many Enterobacteriaceae are pathogens e.g. salmonella, Escherichia coli or involved in spoiling of food produce prior to consumption [13].


Enterobacteriaceae have also been linked to IBS and other inflammatory disease and so it seems lower abundances of these bacteria are to be desired [14]. They are potentially the cause of IBS and to reduce their abundance, artificial sweeteners high in her Slimming World diet should be reduced [14].


Based on the information, my gut seems to have a healthier microbiome than my Mom’s. Many of my microbes should also be keeping me in good health and preventing my obesity. All I can conclude is that my obesity is potentially linked to the high Bacteroides level, or to another factor which I haven’t considered. As Easter approaches, I will think of my gut microbiome before I lift a chocolate egg.


Microbiome research is still trying to determine if a change in the microbiota is actually responsible for a specific condition, or if it is just a ‘side effect.’ The complexity of the gut microbiome, and the fact that each person has a distinct one, makes it extremely difficult to determine cause-effect relationships. As more research is needed, I'm glad to be taking part and possibly helping greatrer understanding in the future. 


Disclaimer: the British Gut Project is not affiliated with this blog and only provided the service of processing the samples' results


Further reading

[1] 23 and me (2019) Meet your genes [Online]. 


[2] Kohli K. (2016) True or False: Muscle weighs more than fat [Online].


[3] British Gut (2019) British Gut [Online]. 


[4] Menni C., Jackson M.A., Pallister T., Steves C.J., Spector T.D., Valdes A.M. (2017). Gutmicrobiome diversity and high-fibre intake are related to lower long-term weight gain. International Journal of Obesity, 41:1099-1105.


[5] Miquel S., Martin R., Rossi O., Bermùdez-Humaràn L.G., Chatel J.M., Sokol H., Thomas M., Wells J.M., Langella P. (2013) Faecalibacterium prausnitzii and human intestinal health. Current Opinion in Microbiology, 16:255-261.


[6] Zoetendal E.G., Plugge C.M., Akkermans A.D.L., de Vos W.M. (2003) Victivallis vadensis gen. nov. sp. nov., a sugar-fermenting anaerobe from human faeces. International Journal of Systematic and Evolutionary Microbiology, 53: 211-215.


[7] Gophna U., Konikoff T., Nielsen H.B. (2017). Oscillospira and related bacteria – from metagenonomic species to metabolic features. Environmental Microbiology, 19: 835-841.


[8] Konikoff T., Gophna U. (2016) Oscillospira: a central, enigmatic component of the human gut microbiota. Trends in Microbiology, 24: 523-524.


[9] Martinez I., Lattimer J.M., Hubach, K.L., Case J.A., Yang J., Weber C.G., Louk J.A., Rose D.J., Kyureghian G., Peterson D.A. Haub M.D., Walter J. (2013). Gut microbiome composition is linked to whole grain-induced immunological improvements. The International Society for Microbial Ecology, 7:269-280.


[10] Wang Y., Ames N.P., Tun H.M., Tosh S.M., Jones P.J., Khafipour E. (2016). High molecular weight barley β-Glucan alters gut microbiota towards reduced cardiovascular disease risk. Frontiers in Microbiology, 7:129.


[11] Schwiertz A., Taras D., Schäfer K., Beijer S., Bos N.A., Donus C., Hardt P.D. (2010) Microbiota and SCFA in lean and overweight healthy subject. Obesity, 18:190-195.


[12] Collado M.C., Isolauri E., Laitinen K., Salminen S. (2008) Distinct composition of gut microbiota during pregnancy in overweight and normal-weight women. The American Journal of Clinical Nutrition, 88:894-899.


[13] Baylis C., Uyttendaele M., Joosten H., Davis A. (2011) The Enterobacteriaceae and their significance to the food industry. International Life Sciences Institute, Europe.


[14] Robertson R. (2016) 10 ways to improve you gut bacteria based on science [Online].