How to Fix Your Gut to Lose Weight and Improve Health?

Serdar Tuncali
Oct 26 · 6 min read

Currently, there are two big camps of obesity research. One camp subscribes to the calories-in-calories-out model of obesity, whereas the other camp believes in the carbohydrate-insulin model. What if there was a third explanation?

Photo by Karley Saagi from Pexels

Did you know that we have as many bacteria as the number of human cells? (1)

We have a 50:50 partnership with the bacteria living in our body and it is not a far-fetched idea to think they call some of the shots.

Even though bacteria reside everywhere on our body, the vast majority is in our gut. We already know that gut microbiota plays a role in digestion, vitamin production, and immune system. What is recently being discovered is the role of gut microbiota in obesity.

Is it possible that our gut microbiota decides our weight? If so, what can we do to change it?

Infants get introduced to gut microbiota during birth. Babies born naturally get their gut microbiota from the mother’s vaginal canal. Additionally, they get bacteria from breast milk and as they grow up, from the environment and foods they eat.

Majority of gut bacteria belongs to one of two main types of bacteria. They are called Firmicutes and Bacteroidetes. The ratio of these two bacteria seems to be different in obese and lean people. (2) Obese people have a higher Firmicutes-to-Bacteroidetes ratio than lean people.

Why does this ratio change and what can we do to reverse it?

Even though the gut microbiota can be affected by genetics, geography, and environment(3), other factors such as the method of birth(4), breastfeeding(5), antibiotic usage(6), and diet(7) can also change the bacterial composition.

Most research on gut microbiota is done on animals. These studies confirm that following a high-sugar, high-fat Western diet increases the Firmicutes to Bacteroidetes ratio in mice(8).

What about research on humans?

Human studies show that lean people have a much diverse bacterial population compared to obese people. (9) Furthermore, when the gut microbiota of these people was transplanted to mice, obese people’s bacteria made the mice obese, whereas lean people’s bacteria made the mice lean. (10)

Interestingly, obese mice didn’t consume significantly more food than lean mice. One explanation for this would be that “obese bacteria” harvest more energy from the foods compared to the “lean bacteria”. (11)

What does all this mean for us? What can we do to change our gut microbiota to “lean bacteria”?

First of all, the research is not yet fully conclusive. There need to be more controlled human trials to be sure of how bacteria affect our weight. However, we can still aim to improve our gut microbiota. Here are some ways to change the bacterial population:

Probiotics: These are actual living organisms. The best sources of probiotics are yogurt, fermented foods, and nutritional supplements. Some probiotic supplementation has shown promising results against obesity. (12)

Prebiotics: This is different from probiotics. Prebiotics are fibers that gut bacteria feed on. Some foods such as garlic, onion, bananas, apples, and asparagus contain prebiotics. Even though there is no clear evidence of prebiotics on weight loss, studies confirm the health benefits of prebiotic consumption. (13)

Fecal Microbiota Transplantation: Fecal Microbiota Transplantation (FMT) is the transfer of fecal bacteria of a healthy donor to the recipient by stool transplantation. We are still at the early stages of this procedure and the effects are not clear yet. We will probably get more answers in 2021 after completion of a clinical trial on FMT. (14)

Diet: It has been shown that long-term dietary patterns can change the gut microbiota population. (15) Consumption of sugar, fiber, fat, and animal proteins have different effects on different strains of bacteria. This data indicates that the type of foods we eat feed different types of bacteria. If we consume the types of foods that feed the “lean bacteria” and starve the “obese bacteria”, we can eventually change the bacterial population in our gut.

It is not yet clear which foods feed the “lean bacteria” and which ones feed the “obese bacteria”. However, the evidence shows the benefits of following a diet rich in fruits, vegetables, fiber, plant protein, monounsaturated fats, and polyunsaturated fats. Whereas diets rich in animal proteins, saturated fats, refined grains, sugar, salt, alcohol, and high fructose corn syrup have detrimental effects on the gut microbiota. (16)

Whether you need to lose weight or not, improving your gut microbiota will have positive health effects on both you and your future children. Here are my top 7 actionable steps to improve your gut:

  1. Increase your fiber intake.
  2. Consume less sugar and artificial sweeteners.
  3. Focus more on plant proteins.
  4. Consume yogurt and fermented foods.
  5. Eat more prebiotic foods.
  6. Take a probiotic supplement.
  7. Avoid unnecessary antibiotic usage.


  1. Ley, R. E., Turnbaugh, P. J., Klein, S., & Gordon, J. I. (2006). Microbial ecology: human gut microbes associated with obesity. nature, 444(7122), 1022.
  2. Gupta, V. K., Paul, S., & Dutta, C. (2017). Geography, ethnicity or subsistence-specific variations in human microbiome composition and diversity. Frontiers in microbiology, 8, 1162.
  3. Huh, S. Y., Rifas-Shiman, S. L., Zera, C. A., Edwards, J. W. R., Oken, E., Weiss, S. T., & Gillman, M. W. (2012). Delivery by caesarean section and risk of obesity in preschool age children: a prospective cohort study. Archives of disease in childhood, 97(7), 610–616.
  4. Bezirtzoglou, E., Tsiotsias, A., & Welling, G. W. (2011). Microbiota profile in feces of breast-and formula-fed newborns by using fluorescence in situ hybridization (FISH). Anaerobe, 17(6), 478–482.
  5. Keeney, K. M., Yurist-Doutsch, S., Arrieta, M. C., & Finlay, B. B. (2014). Effects of antibiotics on human microbiota and subsequent disease. Annual review of microbiology, 68, 217–235.
  6. Wu, G. D., Chen, J., Hoffmann, C., Bittinger, K., Chen, Y. Y., Keilbaugh, S. A., … & Sinha, R. (2011). Linking long-term dietary patterns with gut microbial enterotypes. Science, 334(6052), 105–108.
  7. Turnbaugh, P. J., Bäckhed, F., Fulton, L., & Gordon, J. I. (2008). Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome. Cell host & microbe, 3(4), 213–223.
  8. Turnbaugh, P. J., Hamady, M., Yatsunenko, T., Cantarel, B. L., Duncan, A., Ley, R. E., … & Egholm, M. (2009). A core gut microbiome in obese and lean twins. nature, 457(7228), 480.
  9. Ridaura, V. K., Faith, J. J., Rey, F. E., Cheng, J., Duncan, A. E., Kau, A. L., … & Muehlbauer, M. J. (2013). Cultured gut microbiota from twins discordant for obesity modulate adiposity and metabolic phenotypes in mice. Science (New York, NY), 341(6150).
  10. Turnbaugh, P. J., Ley, R. E., Mahowald, M. A., Magrini, V., Mardis, E. R., & Gordon, J. I. (2006). An obesity-associated gut microbiome with increased capacity for energy harvest. nature, 444(7122), 1027.
  11. Mills, S., Lane, J. A., Smith, G. J., Grimaldi, K. A., Ross, R. P., & Stanton, C. (2019). Precision Nutrition and the Microbiome Part II: Potential Opportunities and Pathways to Commercialisation. Nutrients, 11(7), 1468.
  12. Gibson, G. R., Hutkins, R., Sanders, M. E., Prescott, S. L., Reimer, R. A., Salminen, S. J., … & Verbeke, K. (2017). Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature reviews Gastroenterology & hepatology, 14(8), 491.
  14. Wu, G. D., Chen, J., Hoffmann, C., Bittinger, K., Chen, Y. Y., Keilbaugh, S. A., … & Sinha, R. (2011). Linking long-term dietary patterns with gut microbial enterotypes. Science, 334(6052), 105–108.
  15. Mills, S., Stanton, C., Lane, J. A., Smith, G. J., & Ross, R. P. (2019). Precision nutrition and the microbiome, Part I: Current state of the science. Nutrients, 11(4), 923.

Serdar Tuncali

Written by

Scientific approach to fat loss and body transformation. Self-experimenting and researching various methods and reporting on

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