Gut Health Is Important for Weight Loss

Research makes it clear that taking care of your gut is crucial for achieving and maintaining a healthy weight.

A hand holding a fork over a bowl of chickpeas, vegetables, and quinoa, a meal high in probiotics that's good for gut health and weight loss
Caitlin Beale, MS, RDN
— Signos
Health & Nutrition Writer
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Updated by

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Science-based and reviewed

May 28, 2023
November 22, 2021
— Updated:

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If it feels like everyone’s talking about gut health, it’s because they are. Since the beginning of the human microbiome project<sup>1</sup> in 2008, interest in the magical, symbiotic relationship between our gut bacteria and our health continues to grow. 

Name a chronic disease, and you can probably find a study linking it to a compromised gut, including obesity. We still have a lot to learn about the gut health and weight loss connection. 

Still, the existing research makes it clear that taking care of your gut is an essential piece of achieving and maintaining a healthy weight.

As research digs deeper, it’s possible that the types of bacteria found in your gut may help predict obesity<sup>2</sup> and even how well you will respond to different eating patterns for weight loss. 

How does this work, and what can you do to optimize your gut health? We share the details below. 

What Makes a Healthy Gut?

Gut health is more than digesting your food without bloating or bathroom issues (although this is important!). A healthy gut is diverse<sup>3</sup>, with many types of beneficial bacteria in healthy ratios.

But let’s take a step back even further. Your gut microbiome<sup>4</sup> is made up of trillions of bacteria, fungi, and other microorganisms. They exist entirely separate from us with their own genetic material, and outnumber human cells<sup>5</sup> nearly ten to one. Over time, we have evolved with the bacteria as it’s become an essential part of our bodies.

The primary functions of your gut bacteria<sup>6</sup> include:

  • Immune system training and regulation 
  • Protection against pathogens
  • Vitamin synthesis
  • Support for digestion and absorption
  • Fermentation of dietary fiber to produce beneficial metabolites called short-chain fatty acids (SCFAs)
  • Maintaining the structural integrity of your gut barrier

The health of your microbiome is also closely linked to many health conditions<sup>7</sup>, from brain and skin health to cardiovascular disease. 

Your gut plays a role in neurotransmitter production and the synthesis of hormones that affect feelings of satiety and hunger<sup>8</sup>. It can even influence how many calories you obtain, use, and store<sup>9</sup> from the food you eat.

What Impacts the Health of Your Gut?

Keeping bacteria happy and thriving is vital for a healthy gut, but the colonization of your microbiome starts before you are born. You are introduced to your mother’s bacteria inside the placenta<sup>10</sup>. 

The foundation of your microbiome is also influenced by the way you come into the world. Vaginal deliveries expose you to a much more diverse array of flora from your mother as you move down the birth canal versus a c-section delivery in a sterile environment. 

In fact, some studies suggest that c-section babies are more likely to have allergies, asthma, and even may be at an increased risk for obesity<sup>11</sup> later in life.

Your microbiome remains fluid for the first few years of life. It is further influenced by breastmilk and introduction to first foods. Breast milk provides unique microorganisms<sup>12</sup> from the mom, while formula-fed babies miss out on these benefits. 

By the time you reach ages three to five, the microbiome is relatively established<sup>13</sup>, although certain factors can influence it as you age, including:

  • Medications like antibiotics, antacids, or aspirin
  • Stress
  • Sleep habits
  • Exercise
  • Illness or food poisoning

But the number-one predictor of bacterial diversity is your diet<sup>14</sup>. Since gut bacteria feed and ferment fiber, high-fiber diets<sup>15</sup> full of many different plant-based foods like vegetables, fruits, nuts, seeds, and whole grains are associated with more healthy bacteria. 

This is fantastic news because it means you can help your microbiome thrive with healthy diet and lifestyle choices.

What’s the Link Between Gut Health and Weight Loss?

Since your gut bugs appear to be involved in all aspects of health, it’s not hard to see a connection with weight. While animal studies don’t always translate to human studies, a study on mice displays a fascinating relationship between gut health and weight loss. 

The study collected bacteria from lean and obese twin female mice. The bacteria were transplanted into genetically similar, germ-free mice (meaning they didn’t have any bacteria before the microbes were added) who ate the same diet. 

In this study, mice who received bacteria from obese women gained more weight and had a less diverse microbiome<sup>16</sup> despite eating the same foods. And even more interesting, once the mice were moved into a shared cage where they shared microbes, neither group gained weight.

But why did this happen? While the science is complex, there are several ways scientists think bacteria can influence your weight.

A man holding a bottle of kombucha, a drink high in probiotics for a healthy gut

A Balanced Microbiome Matters for Healthy Weight 

Early research on gut health and weight loss started with twin studies. Twins make ideal subjects for scientific studies because they share the same genes, making it easier to control individual differences. 

Researchers found that twins with lean body types had many more bacterial species<sup>17</sup> than those with obesity. The ratio of two primary species, Bacteroides and Firmicutes, also looked different for both groups. Thin people tended to have more Bacteroides while Firmicutes increased with obesity.

However, the research on Bacteroides is mixed. While numbers may be higher for lean people, it’s more likely that the balance of this species in relation to other beneficial bacteria matters more. 

One study found that the ratio of Bacteroides and Prevotella, another commensal bacteria, helped predict weight loss. After following a high-fiber diet, people with a higher proportion of Prevotella to Bacteroides lost more weight<sup>18</sup>. 

Similar results were seen in a study that found that participants with higher Prevotella to Bacteroides ratios could lose more weight and body fat<sup>19</sup>, regardless of their diet patterns.

But too much of any type of bacteria isn’t a good thing. Remember that gut health is related to diversity. So even so-called good bacteria in higher-than-average amounts can be a problem because it affects the overall ratio. For example, high levels of certain types of Prevotella are also associated with inflammation<sup>20</sup>.

Feel confused? Remember, it’s all about balance. Just like a healthy diet relies on many different types of nutrients, the diversity of bacteria matters most. Less bacterial richness is associated with obesity<sup>21</sup>.

Gut Bacteria Can Hack Your Hormones and Metabolism

Another way your microbiome can influence your weight is through the synthesis of hormones that regulate your appetite. Leptin, known as the satiety hormone, and ghrelin<sup>22</sup>, a hormone that sends hunger signals to your brain, are both modulated by gut bacteria. 

The bacteria present may also help you better digest<sup>23</sup> certain beneficial plant compounds and affect how you digest, absorb, and store nutrients. 

Some research suggests that obese people have a bacteria profile that can absorb more calories from food<sup>24</sup>.

Certain Types of Bacteria Could Predict Weight Loss

Some research suggests that your baseline microbiome can influence your ability to lose weight. 

One study gave subjects a low-calorie diet and found significant differences in the microbiomes of those who could lose more weight<sup>25</sup> than those who didn’t.

A study found that specific microbial gene patterns<sup>26</sup> were associated with an increased ability to lose weight, independent from diet or certain factors like BMI or age.

Another 2021 study found that baseline gut microbiota was a significant predictor of weight loss<sup>27</sup>. Weight loss also yielded substantial, positive changes in the bacteria.

The question remains whether we can test and target a person’s microbiome to create an individualized weight loss program, but much more research is needed.

How Does Gut Bacteria Impact Your Blood Sugar?

More recently, researchers have turned their attention to another type of bacteria called Akkermansia<sup>28</sup>. Though it has many roles in the body, it appears that this bacteria is closely linked to metabolic health. Several studies found associations between low levels of Akkermansia and weight gain<sup>29</sup> and altered glucose metabolism. 

Akkermansia is also essential for SCFA production, the metabolites created when bacteria ferment fiber. Butyrate<sup>30</sup>, a SCFA, is associated with a healthy metabolism and is needed for glucose control.

Some research suggests that people with type 2 diabetes have low butyrate production and low levels of Akkermansia, both connected to blood sugar balance and weight gain<sup>31</sup>. In fact, supplementing with a probiotic that includes strains of Akkermansia may lead to better glucose control.

<p class="pro-tip">Read more about probiotics and blood sugar</p>

Can You Test for Gut Health?

There is no gold-standard test to measure dysbiosis or an imbalance of gut bacteria.

There are physical signs that something may be off with your gut, such as:

  • Constipation
  • Bloating
  • Diarrhea
  • Undigested food in your stools
  • Stomach pain
  • Gas

But dysbiosis can also lead to symptoms outside of the gut, such as brain fog, fatigue, or skin issues. 


Testing for gut health

There isn’t a perfect test for gut microbiome health. Basic stool tests ordered by your doctor will look for parasites, gut inflammation, or the presence of things that shouldn’t be there, like high levels of fat. But they don’t test your gut bacteria, and they wouldn’t be ordered if you are just interested in learning about your microbiome but don’t have specific symptoms.

There are stool tests that you can order with trained health care practitioners or even direct-to-consumer options that look for patterns of bacteria found in the stool. This can be helpful to see if you have more or less of a particular type of bacteria to support diversity. These tests usually have you collect stool samples. 

But there are questions about the accuracy of these tests and what they really tell you since there isn’t a known optimal set range or number of bacteria. And the direct-to-consumer options may be challenging to fully interpret.

So if you are concerned with your gut health, it’s a good idea to work with someone who specializes in gut health to help you work through your options.

How Can You Improve Your Gut Health?

Like any aspect of health, a balanced gut relies on a holistic approach to wellness, including sleep, stress management, diet, and exercise. Each of these habits could be an article on its own, but since diet is the main predictor, we will focus on what you can eat for a healthy gut. 

A close up shot of a bowl of kimchi, fermented vegetables that are high in probiotics, which contribute to gut health

Best Foods for Gut Health and Weight Loss 

Since your diet is the number-one predictor of bacterial richness and diversity, making good food choices can support your gut health while helping with weight loss goals.

Diets high in prebiotic fibers, the fuel for your microbes, are critical for a healthy gut. Plus, they are rich in polyphenols and antioxidants that help reduce inflammation in the body.

Foods<sup>33</sup> to support your gut health include:

  • Fermented vegetables 
  • Yogurt
  • High-fiber fruits and vegetables 
  • Herbs and spices
  • Plant-based oils
  • Nuts and seeds 
  • Whole grains

Foods to avoid for gut health<sup>34</sup> include:

  • Sugar 
  • Artificial sweeteners 
  • Processed foods
  • Refined seed oils

Best Supplements for Gut Health and Weight Loss

Probiotics are a hot topic and one of the most popular supplements for gut health. Studies are mixed on whether probiotic supplementation helps with weight loss. 

One review suggests that in combination with other gut-supporting supplements like prebiotics, probiotics could have a small but significant positive impact on weight loss<sup>35</sup>.

The truth is that the best probiotic for gut health and weight loss is individualized and strain-specific to you. That means it helps support or replace missing microbes or support specific health conditions like irritable bowel syndrome<sup>36</sup>.

That said, a broad strain with multiple types and high amounts of bacteria (called colony-forming units or CFU) could be a way to support your gut health and weight loss. Or look for one that includes Akkermansia, especially if you want to target blood sugar support with weight loss. 

Gut Health and Weight Loss Final Thoughts

While we may not know the “perfect” ratio of bacteria to support a healthy weight, we know diversity and balance are key. 

Get started by bumping up fiber and fermented veggies in your diet and possibly adding a probiotic. If you struggle with any digestive symptoms, make sure you reach out to someone who specializes in gut health to help you get back on track.


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About the author

Caitlin Beale is a registered dietitian and nutrition writer with a master’s degree in nutrition. She has a background in acute care, integrative wellness, and clinical nutrition.

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Please note: The Signos team is committed to sharing insightful and actionable health articles that are backed by scientific research, supported by expert reviews, and vetted by experienced health editors. The Signos blog is not intended to diagnose, treat, cure or prevent any disease. If you have or suspect you have a medical problem, promptly contact your professional healthcare provider. Read more about our editorial process and content philosophy here.

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