The link between your gut microbiome and your weight

Your gut is home to trillions of bacteria, collectively known as the gut microbiome, which wears several hats when it comes to your overall health. Though this may sound alarming, these organisms are actually there to help your body carry out multiple functions to keep you thriving. Recent research has shown that the gut microbiome may also play a significant role in managing body weight and even influence the success of weight loss efforts, reinforcing the need for us to keep the organisms inside of us healthy.¹ 

Gut bacteria and weight loss

Your gut microbiome is one of the most complex systems in the human body. To this day, scientists are still researching the many ways it affects us. So far, research has found that the ratio of two types of gut bacteria, Prevotella and Bacteroides, may be linked to how easily you can lose weight.² 

• Prevotella: These bacteria are known to thrive on a diet rich in fibre and complex carbohydrates, such as fruits, vegetables, and whole grains. They are particularly efficient at breaking down dietary fibres, which leads to the production of short-chain fatty acids (SCFAs) —beneficial compounds that can reduce inflammation, improve gut health, and may play a role in enhancing fat metabolism.²

• Bacteroides: These bacteria are more commonly associated with diets high in animal fat and protein.² While they also aid in digestion, they may not be as efficient in producing SCFAs or supporting fat breakdown as Prevotella.

In a study where participants followed a calorie-controlled diet, those with a higher proportion of Prevotella bacteria compared to Bacteroides were able to lose more weight and body fat than individuals with a more balanced ratio of these bacteria.³ There are two reasons as to why this could happen:

1. Prevotella bacteria are highly effective at breaking down dietary fibres into SCFAs, which can help with appetite regulation, reduce fat storage, and improve overall metabolism.³ This means that people with more Prevotella bacteria might be better at converting fibre into energy and less likely to store excess fat.

2. SCFAs produced by Prevotella have been linked to improved insulin sensitivity.⁴ When your body responds better to insulin, it can regulate blood sugar levels more effectively, reducing the risk of fat accumulation and making it easier to lose weight.

The role of the gut microbiome in obesity

Being overweight or obese is associated with several chronic health conditions, such as cardiovascular diseases, diabetes, and cancer. While factors such as diet, genetics, and lifestyle play a role in weight gain, imbalances in the gut microbiome may also contribute to obesity.⁵

When the balance of gut bacteria is disrupted, a condition known as gut dysbiosis, harmful bacteria can thrive, potentially leading to chronic inflammation.⁶ Interestingly, studies have shown that obese individuals tend to have a higher ratio of Firmicutes—another abundant bacteria found in the gut—compared to Bacteroidetes, a pattern that differs from those with a healthy weight.⁶ 

One explanation for this is that Firmicutes are more efficient at extracting energy from food, particularly from non-digestible carbohydrates like dietary fibre.⁷ This means that if you have a higher proportion of Firmicutes, your body might absorb more calories from the same amount of food, leading to increased fat storage.⁷ These bacteria also promote the production of SCFAs, which though are essential for gut health, can also provide extra calories, which may contribute to weight gain and difficulty in losing weight over time.

On the contrary, Bacteroidetes are thought to play a more protective role by aiding in digestion without promoting excess fat accumulation.⁶ Some studies suggest that increasing the number of Bacteroidetes through a high-fibre diet can improve weight loss outcomes, as these bacteria are more prominent in individuals who follow plant-based, fibre-rich diets.

Obesity and gut inflammation

When harmful bacteria in your gut produce toxins, like lipopolysaccharides, they can slip through the gut lining if it’s weakened.⁸ This sets off your immune system and leads to inflammation. Over time, chronic inflammation can cause your cells to become resistant to insulin, which means your body struggles to manage blood sugar properly, and consequently it becomes harder to control your weight.⁸

Gut dysbiosis can also mess with important hormones like leptin and ghrelin, which help regulate hunger and fullness.⁹ When leptin isn’t working as it should, your brain doesn’t get the message that you have enough stored fat, leading to overeating. At the same time, higher ghrelin levels can increase your hunger, making it more challenging to stick to healthy eating habits.

How your gut influences weight loss

The bacteria in your gut play a surprising role in how your body responds to weight loss efforts. Understanding these connections may help you improve your weight loss outcomes by supporting a healthy and balanced gut.

1. Gut diversity and energy extraction

A diverse gut microbiome can help you get the most out of the food you eat.¹⁰ A wide variety of bacteria in your gut ensures that food is broken down efficiently, and energy is extracted properly. Research suggests that eating a varied diet with plenty of fruits, vegetables, and whole grains helps keep your microbiome balanced and diverse, which is essential for both digestion and energy conversion.¹¹

2. Regulating appetite hormones

Your gut bacteria play a role in controlling the hormones that regulate hunger and fullness—ghrelin and leptin. Some evidence suggests that having a healthy gut may reduce ghrelin levels, potentially curbing your appetite.⁹

3. Production of SCFAs

Gut bacteria help produce SCFAsby breaking down dietary fibre. SCFAs provide energy, help you feel fuller for longer, and may even reduce inflammation. Eating more high-fibre foods like fruits and vegetables can promote SCFA production, which is linked to better weight management and improved insulin sensitivity.

4. Fat storage regulation

The bacteria in your gut can influence how much fat your body stores. Some gut bacteria promote fat storage, while others may help reduce it.¹² A balanced gut microbiome could help regulate fat accumulation, making it easier to manage your weight effectively.

The numan take

Your gut microbiome is as unique as your fingerprint. Hence, it’s difficult for science to pinpoint exactly what we should do to keep ours healthy. What we do understand, however, is the impact our diet choices can have on our gut microbiome. Adopting a balanced diet doesn’t just promote weight loss, but can really help your gut microbiome thrive.

References

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2. Hjorth MF, Blædel T, Bendtsen LQ, Lorenzen JK, Holm JB, Kiilerich P, et al. Prevotella-to-Bacteroides ratio predicts body weight and fat loss success on 24-week diets varying in macronutrient composition and dietary fiber: results from a post-hoc analysis. Int J Obes (Lond) [Internet]. 2019 [cited 2024 Sep 9];43(1):149–57. Available from: https://www.nature.com/articles/s41366-018-0093-2

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