Is your gut flora making you fat?

Thousands of people struggle to lose weight, frequently succeeding in the short term only to put it back on, with interest! If this sounds familiar, you’ll be interested to know that there may be more to it than just the food choices you’re making.

Nutritional science is constantly evolving and as we learn more about the gut microbiome there is increasing evidence that the trillions of bacteria in our gut may have a direct impact on our weight.

Studies have shown that the gut flora composition of obese and diabetic people is different to those of a lean person. And while the microbial profile may be similar between members of the same families, it can differ enormously from person to person. This is because there are around 100 trillion micoorganisms in the gut from more than 400 recognised species, so it’s little wonder that no two guts are ever the same profile!

Obesity it seems may be related not just to differences in the strains of bacteria but also to the diversity of species, which appears to be reduced compared to a lean person’s gut profile. This may influence both appetite and metabolic rate.

One study (conducted with mice) found that the mice with higher levels of ‘bad bacteria’ had a bigger appetite (or an inability to switch off appetite) resulting in them eating 10% more food than those with a more beneficial balance of gut flora. 

This increase in bad bacteria is likely to be due to the absence of a compound called TLR5. Toll-like Receptor 5 (TLR5) is a protein in the gut that helps manage levels of bacteria, keeping bad bacteria levels down. But without it, levels increase leading to influences on appetite hormones and inflammation that contribute to weight gain. 

It also appears that the adverse balance of bacteria in obese subjects influences increased energy extraction from food (absorbing more calories), promotion of fat deposition, and systemic inflammation.

Diet also influences the balance between good and bad bacteria. The preferred food source for bad bacteria is sugar, so diets high in refined carbohydrates, sugars and processed foods will contribute to the imbalance, in turn contributing to weight gain. Over-consumption of refined carbohydrates, sugars and processed foods are, of course, also linked to an increase in fat mass due to the pressure they put on insulin release which influences fat storage, and for these reasons should be avoided by anyone looking to lose weight.

There is some evidence suggesting that consumption of the correct probiotics can aid weight-loss, with studies showing specific strains may be involved in influencing weight. So taking advice on the use of probiotic supplementation is recommended. 

If you’re in doubt as to how to assimilate this thinking into your weight-loss programme, visit a nutritional therapist. They will be able to help put together an effective gut-balancing programme alongside an appropriate dietary plan to help you along the road to your weight-loss goals.


Cani PD, Delzenne NM (2009) Interplay between obesity and associated metabolic disorders: new insights into the gut microbiota. Current Opinion in Pharmacology, 9: 737-743.

Delzenne et al (2011) Targeting gut microbiota in obesity: effects of prebiotics and probiotics. Nature Reviews Endocrinology, 7:639-646.

DiBaise et al (2008) Gut microbiota and its possible relationship with obesity. Mayo Clinic Proceedings, 83(4): 460-469.

Tsai F, Coyle WJ (2009) The microbiome and obesity: Is obesity linked to our gut flora? Current Gastroenterology Reports, 11(4): 307-313.

Turnbaugh et al (2008) A core gut microbiome in obese and lean twins. Nature, 457: 480-484.

Vijay-Kumar et al (2010) Metabolic syndrome and altered gut microbiota in mice lacking Toll-like receptor 5. Science Magazine, 328 (5975): 228-231.

Nutritionist Resource is not responsible for the articles published by members. The views expressed are those of the member who wrote the article.

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Farnham GU9 & Alton GU34

Written by Sarah Brown

Farnham GU9 & Alton GU34

I am an experienced Registered Nutritional Therapist (mBANT) with clinics in Alton and Farnham. I work with clients across the UK via Skype,  with face to face consultations in Surrey (when permitted). Having graduated 9 years ago from the University of West London after studying at the renown...

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