Science-based and reviewed
If it feels like everyone’s talking about gut health, it’s because they are. Since the Human Microbiome Project began in 2008, interest in the magical, symbiotic relationship between our gut bacteria and our health continues to grow.1
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 gut health and weight loss connection.
Still, the existing research clarifies that caring for your gut is essential to achieving and maintaining a healthy weight.
As research digs deeper, the types of bacteria found in your gut may help predict obesity and even how well you will respond to different eating patterns for weight loss.2
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, with many types of beneficial bacteria in healthy ratios.3
Your gut microbiome is made up of trillions of bacteria, fungi, and other microorganisms.3 They exist entirely separate from us with their own genetic material and outnumber human cells nearly ten to one.4 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 include:5
- 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, from brain and skin health to cardiovascular disease.6
Your gut plays a role in neurotransmitter production and the synthesis of hormones that affect feelings of satiety and hunger.7 It can even influence how many calories you obtain, use, and store from your food.8
Keeping bacteria happy and thriving is vital for a healthy gut, but colonizing your microbiome starts before birth. You are introduced to your mother’s bacteria inside the placenta.9
The foundation of your microbiome is also influenced by how 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.
Some studies suggest that c-section babies are more likely to have allergies and asthma and may even be at an increased risk for obesity later in life.10
But the number-one predictor of bacterial diversity in your diet.11 Since gut bacteria feed and ferment fiber, high-fiber diets full of many different plant-based foods like vegetables, fruits, nuts, seeds, and whole grains are associated with healthier bacteria.12
This is fantastic news because you can help your microbiome thrive with a healthy diet and lifestyle choices.
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How Poor Gut Health Affects Weight Loss
Since gut bacteria 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 despite eating the same foods.13 And even more interesting, once the mice were moved into a shared cage where they shared microbes, neither group gained weight.
Another way your microbiome can influence your weight is by synthesizing hormones that regulate your appetite. Leptin, known as the satiety hormone, and ghrelin, a hormone that sends hunger signals to your brain, are both modulated by gut bacteria.19
The bacteria present may also help you better digest certain beneficial plant compounds and affect how you digest, absorb, and store nutrients.20
Some research suggests that obese people have a bacteria profile that can absorb more calories from food.21
Some research also 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 than those who didn’t.22
A study found that specific microbial gene patterns were associated with an increased ability to lose weight, independent of diet or certain factors like BMI or age.23
Another 2021 study found that baseline gut microbiota was a significant predictor of weight loss.24 Weight loss also yielded substantial, positive changes in the bacteria.
Whether we can test and target a person’s microbiome to create an individualized weight loss program remains, but much more research is needed.
A Balanced Microbiome 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 than those with obesity.14 The ratio of two primary species, Bacteroides and Firmicutes, also looked different for both groups. Thinner 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.15
Similar results were seen in a study that found that participants with higher Prevotella to Bacteroides ratios could lose more weight and body fat, regardless of their diet patterns.16
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 problematic because it affects the overall ratio. For example, high levels of certain types of Prevotella are also associated with inflammation.17
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.18
Gut Bacteria and Blood Sugar
More recently, researchers have turned their attention to another type of bacteria called Akkermansia.25 Though it has many roles in the body, it appears this bacteria is closely linked to metabolic health. Several studies found associations between low levels of Akkermansia and weight gain and altered glucose metabolism.26
Akkermansia is also essential for SCFA production, the metabolites created when bacteria ferment fiber. Butyrate, an SCFA, is associated with a healthy metabolism and is needed for glucose control.27
Some research suggests that people living with type 2 diabetes have low butyrate production and low levels of Akkermansia, both connected to blood sugar balance and weight gain.28 In fact, supplementing with a probiotic that includes strains of Akkermansia may lead to better glucose control.
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
However, dysbiosis can also lead to symptoms outside the gut, such as brain fog, fatigue, or skin issues.
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 fat levels. 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 these tests' accuracy and what they tell you since there isn’t a known optimal set range or a number of bacteria. Also, the direct-to-consumer options may be challenging to interpret fully.
So, if you are concerned with your gut health, it’s a good idea to work with someone specializing in gut health to help you work through your options.
6 Ways How You Can Improve 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.
Slowly build up your fiber intake
High-fiber foods, such as oatmeal, berries, and legumes, are filling, support blood sugar regulation, and contain indigestible carbs that support a healthy gut microbiome. Fiber is also vital for producing beneficial SCFAs. Aim to fill half of your plate with fruits and vegetables and work your way up to 30 grams of fiber a day.
Make your diet more diverse
Research shows that eating 30 types of plant-based foods per week can boost gut diversity.33
Some ways to reach this goal are to:
- Buy mixed beans instead of black beans
- Get mixed nuts instead of one type
- Add chia seeds to oatmeal or salads
- Add mixed greens and fruit to smoothies
Start taking a probiotic supplement
To boost the diversity of your gut, consider taking a probiotic supplement that contains multiple strains of bifidobacterium and lactobacillus. While research findings are mixed, one review of 25 randomized human trials found that probiotic supplementation reduced BMI and body weight.34
Eat fermented foods
Fermented foods, like kefir and kimchi, can help populate the gut microbiome. In a 2021 trial, individuals who ate an average of six servings of fermented foods daily improved their gut diversity and decreased inflammation markers in 10 weeks.35 Ways to integrate these foods into your meals include:
- Add a kombucha to your routine
- Eat plain yogurt with berries as a snack
- Add a scoop of sauerkraut or kimchi to salads
Set limits on alcohol, sugar, and processed foods
Alcohol, excess sugar, and processed foods can promote gut dysbiosis, leading to metabolic dysregulation and weight gain. Moderate these items and aim for a balanced plate of whole foods.
Learn how to manage stress
Chronic, high stress can decrease gut diversity. Schedule intentional time for self-care that may include meditation, time outside, or a reading break.
Foods to Eat and Avoid 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.
Foods to support your gut health include:29
- 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 include:30
- Sugar
- Artificial sweeteners
- Processed foods
- Refined seed oils
The Role of Supplements on 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, combined with other gut-supporting supplements like prebiotics, probiotics could have a small but significant positive impact on weight loss.32
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.33
A broad strain with multiple types and high amounts of bacteria (colony-forming units or CFU) could 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, diversity, and balance are key.
Start by bumping the fiber and fermented veggies into your diet and adding a probiotic. If you struggle with digestive symptoms, contact someone specializing in gut health to help you get back on track.
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