Our guts harbour many different species of bacteria. In fact we have 10 times as many bacterial cells in our guts than the cells that make up our bodies! (1) These microbes are known as the gut microbiome and are involved in a number of processes from digestion and immunity to producing certain vitamins. Research is increasingly focused on the role they play in weight gain and the development of obesity.
Whilst your guts contain hundreds of different species of bacteria, there are two main types. One is the bacteroidetes. Slim people have more of these. The other is the firmicutes. If you have more of the firmicutes bacteria, you are likely to carry more weight. (2)
So how do your gut bacteria affect your weight?
If you are overweight, you are likely to have an imbalance between the different types of bacteria in your gut - so you have a greater ratio of firmicutes bacteria to bacteroidetes. (3) This bacterial imbalance can increase your appetite by making you resistant to the hormone leptin, that regulates your appetite. This makes you want to eat more. The firmicutes bacteria are also able to extract more calories from what you eat. (4)
Let’s say Alice has a different gut bacterial balance than her friend, who is slim. As a result, Alice probably wants to eat more than Mia. But even if she ate exactly the same amount, she would obtain more calories from it and gain weight.
On top of that, imbalances in your gut bacteria may slow your metabolism and increase the amount of fat you store. (5) So it’s a triple whammy. Not only do you want to eat more, but you also get more calories from the same food and you burn less fat.
Moreover, gut bacterial imbalances can increase inflammation and increase your gut permeability, which is linked to food intolerances. Both inflammation and food intolerances can lead to weight gain.
Changes in gut bacteria have been found to exist before we gain weight. (6) Could we therefore manipulate gut bacteria to affect the amount of fat we store? Would bacteria received through a fecal transplant from a lean donor help you lose weight? Initial research is promising, and clinical trials are currently being carried out.
But you can also improve your gut bacterial balance through dietary changes.
Here are three changes that can encourage a good bacterial balance:
Include fermented foods as they contain probiotics, which are beneficial bacteria. Fermented foods include live natural yogurt, kefir, cottage cheese, miso, tempeh, kombucha, sauerkraut and kimchi. The Western diet is often low in fermented foods.
Include foods that contain prebiotics. Prebiotics support the growth of beneficial bacteria. Foods that contain prebiotics include onions, garlic, leeks, asparagus, bananas, chicory, oats, peas, beans, lentils and Jerusalem artichoke.
Reduce sugar as it feeds the ‘bad’ bacteria in your gut, exacerbating any bacterial imbalance.
Gut bacterial imbalances are one of a number of imbalances in your body that can make you gain weight. Discover which imbalances are blocking your weight loss and find your personal way to rebalance your body - so you set up the conditions for lasting weight loss and reclaim your health and vitality.
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1 Bull, M.J. and Plummer N.T., 2014, ‘Part 1: The Human Gut Microbiome in Health and Disease’, Integr Med (Encinitas), 13(6), 17–22
2 Ley, R.E. et al., 2006, ‘Microbial ecology: human gut microbes associated with obesity’, Nature, 444, 1022–23.
3 Stojanov, s. Et al., 2020, ‘The Influence of Probiotics on the Firmicutes/Bacteroidetes Ratio in the Treatment of Obesity and Inflammatory Bowel disease’, Microorganisms, 8(11), 1715.
4 Cani, P.D. et al., 2012, ‘Involvement of gut microbiota in the development of low-grade inflammation and type 2 diabetes associated with obesity’, Gut Microbes, 3, 4, 279–88; Jumpertz, R. et al., 2011, ‘Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humans’, Am J Clin Nutr, 94, 1, 58–65.
5 Bäckhed, F. et al., 2007, ‘Mechanisms underlying the resistance to diet-induced obesity in germ-free mice’, Proc Natl Acad Sci USA, 104, 979–84.4
6 Kalliomäki, M. et al., 2008, ‘Early differences in fecal microbiota composition in children may predict overweight’, Am J Clin Nutr, 87, 3, 534–8.