What is the Microbiome, and Does It Really Affect Your Health and Weight?

When people talk about health and well-being these days, the word “microbiome” often pops up. You’ve probably heard it mentioned on podcasts, on TikTok, in Instagram reels, in health magazines, on TV, or maybe even at your doctor’s office. But what exactly is the microbiome, and does it really play a role in your health, or even your weight?

None of this is intended as or should be used as medical advice. If you have a medical condition, always speak to a qualified healthcare professional.

Summary, First?

I am going to start with my conclusion early.

As I did my research for this blog, the common theme I kept finding is that it doesn’t really change the approach I try to take with my nutrition coaching clients.

Whether or not you’re focusing on your gut health, the foundations of a good diet remain the same: eat more whole foods. Whole foods, like fruits, vegetables, whole grains, nuts, seeds, and lean proteins, are naturally rich in fibre, vitamins, and minerals that support overall health, including your gut.

For example, foods like apples, oats, lentils, and brown rice provide soluble fibre, which not only aids digestion but also feeds the beneficial bacteria in your gut, helping them thrive. Leafy greens such as spinach, kale, and broccoli are packed with nutrients and fibre that promote healthy digestion, while fatty fish like salmon provides anti-inflammatory omega-3 fatty acids, supporting both heart and gut health. Fermented foods like yoghurt, kefir, and sauerkraut are naturally probiotic, offering live bacteria that can contribute to a healthy microbiome.

So, incorporating a wide variety of these foods into your daily diet is a tried-and-true way to support not only your gut but your entire body. So, even amidst the buzz around the microbiome, sticking to whole, minimally processed foods is still the best approach to overall well-being – regardless of your gut or microbiome.

I don’t personally advocate cutting out ultra-processed foods completely as sometimes it is not practical or affordable to do so and – let’s be honest – most are pretty nice as a treat and we all deserve a little joy in life. For these reasons, I don’t believe in completely cutting out complete food groups, but do try to keep them to a minimum.

So, now for more detail:

What Is the Microbiome?

The microbiome is essentially a community of tiny organisms, mostly bacteria, that live inside your body. In fact, trillions of bacteria, fungi, viruses, and other microbes are hanging out inside you right now! Most of these little creatures reside in your gut, particularly in your large intestine, and they’re not there just for the ride. They actually do some important work.

Some of these bacteria help digest food, others produce vitamins like B12 and K, and some help fight off harmful invaders. So, while “bacteria” might sound like a bad word, when it comes to the microbiome, many of them are good guys. In a way, you could think of your microbiome as a tiny eco-system that helps keep you healthy.

OK, But What Is The Gut?

The gut, often referred to as the gastrointestinal (GI) tract, is a long, continuous tube that starts at the mouth and ends at the anus. Its primary function is to digest the food we eat, absorb nutrients, and eliminate waste. It consists of several parts, including the stomach, small intestine, and large intestine (or colon), with each playing a crucial role in the digestive process. The stomach breaks down food with the help of acids and enzymes, while the small intestine absorbs most of the nutrients from digested food. The large intestine is responsible for absorbing water and compacting waste for elimination. The gut is also home to trillions of microbes, collectively known as the gut microbiome.

How Does It Impact Your Health?

More and more research suggests that your microbiome has a significant impact on your overall health. For instance, having a diverse and balanced mix of bacteria in your gut is linked to a stronger immune system, better digestion, and even improved mental health. On the flip side, an imbalance—where harmful bacteria take over—has been linked to conditions like obesity, diabetes, heart disease, and inflammatory diseases like Crohn’s or IBS.

It’s not just about digesting your food either. Your microbiome is thought to communicate with other parts of your body, including your brain. Some scientists even call the gut your “second brain,” due to the gut-brain axis. This means the bacteria in your gut could influence how you feel, potentially affecting your mood, stress levels, and even sleep.

What About Weight?

Here’s where things get particularly interesting. Some studies have shown that the composition of your gut microbiome could play a role in how your body processes food, and by extension, your weight. The idea is that certain bacteria are better at extracting calories from food than others, meaning some people may be more efficient at storing fat, simply because of the type of bacteria they have in their gut.

For example, there’s research showing that people who are overweight tend to have a different mix of gut bacteria compared to people who are lean. In some animal studies, transferring bacteria from an overweight mouse to a lean one has actually caused the lean mouse to gain weight, even without eating more.

That said, it’s not as simple as “blame your gut for weight gain.” Many factors contribute to your weight, including diet, lifestyle, genetics, and physical activity. The microbiome might be one piece of the puzzle, but it’s certainly not the whole picture.

Can You Change Your Microbiome?

The good news is that your microbiome isn’t set in stone. The bacteria living in your gut are influenced by what you eat, your environment, and your habits. Eating a varied diet, rich in fibre from fruits, vegetables, and whole grains, can help promote the growth of beneficial bacteria. Fermented foods like yoghurt, kefir, sauerkraut, and kombucha can also give your gut a helpful boost of probiotics (live bacteria).

Avoiding too many processed foods, sugar, and artificial sweeteners can help prevent the growth of harmful bacteria. Also, antibiotics, while sometimes necessary, can wipe out good bacteria along with the bad, so it’s a good idea to replenish your gut with probiotic-rich foods after a course of antibiotics.

What About Cravings? Does It Play a Role?

The bacteria in your microbiome may have more influence on your cravings than you might expect. Research suggests that certain types of gut bacteria can communicate with the brain via the gut-brain axis, potentially impacting the foods you crave. For example, some studies have shown that an imbalance in gut bacteria might lead to stronger cravings for sugary or processed foods. This is because certain bacteria thrive on sugar, and when their population grows, they may send signals that encourage you to eat more of the foods they need to survive, which can perpetuate a cycle of unhealthy eating.

On the flip side, a more diverse and balanced microbiome—supported by a diet rich in fibre, fruits, and vegetables—could help reduce cravings for junk food and promote more stable hunger signals. Fibre-rich foods feed beneficial bacteria that produce short-chain fatty acids, which help regulate appetite by signalling to the brain that you’re full. While the exact relationship between gut bacteria and cravings is still being studied, it appears it is likely that your microbiome plays a role in shaping your food preferences and habits, further highlighting the importance of maintaining a healthy gut for overall well-being.

Could the Science Be Wrong?

While the research on the microbiome is exciting, it’s important to note that it’s still a relatively new field, and we don’t have all the answers yet. Scientists are still piecing together how exactly the microbiome interacts with the rest of the body, and the findings we have so far are not without limitations.

For one thing, much of the current research is based on animal studies, particularly with mice. While these studies provide interesting insights, mice are not humans, and their microbiomes differ from ours. What happens in a mouse’s gut might not perfectly translate to what happens in ours.

There’s also the issue of how complex the microbiome is. The diversity and interactions between the various bacteria in your gut are so vast that it’s difficult to pinpoint specific causes and effects. For example, even though studies have shown correlations between certain bacteria and obesity, correlation doesn’t always mean causation. It’s still unclear whether an unhealthy microbiome directly causes weight gain, or if being overweight changes your microbiome.

Finally, the impact of lifestyle factors, like diet and exercise, often overlaps with microbiome research. It’s hard to separate the influence of the microbiome from these other important factors. So, while gut health seems to be a piece of the puzzle, it’s likely just one of many interconnected factors that affect your overall well-being.

Studies Supporting the Microbiome’s Role in Health and Weight

Several studies have highlighted how the gut microbiome can influence overall health and weight. Here are a few key examples:

Turnbaugh et al. (2006) conducted a famous study showing that the microbiome in obese mice is different from lean mice, and that transferring the gut bacteria from obese mice into lean mice caused the lean ones to gain weight, even without a change in diet. This study suggests that gut bacteria can influence the efficiency of calorie absorption.
Ridaura et al. (2013) demonstrated a similar effect in humans by transplanting gut bacteria from obese people into mice. The mice receiving bacteria from the obese individuals gained more fat than those receiving bacteria from lean individuals, highlighting a link between microbiome composition and fat storage.
Vogtmann et al. (2016) found that people with higher gut bacterial diversity were generally healthier, with lower risks of conditions like diabetes, heart disease, and obesity, suggesting that the health of the microbiome may be crucial in preventing disease.
Bäckhed et al. (2004) observed that germ-free mice, which lack a gut microbiome, were resistant to obesity even when fed a high-fat diet, while normal mice became obese. This finding supports the idea that gut bacteria help regulate weight gain.

Studies Questioning the Microbiome’s Role

While the science is promising, not all studies are conclusive, and some raise questions about the extent of the microbiome’s influence:

Sze and Schloss (2016) conducted a meta-analysis of human studies and found that while there is an association between obesity and microbiome composition, the differences between individuals are often small, and not all studies show significant links between gut bacteria and body weight.
Mullin et al. (2018) argued that many studies on the microbiome and weight rely heavily on animal models or observational data in humans. They suggest that factors such as diet, exercise, and lifestyle may have a larger influence on weight than the microbiome alone.
Walter et al. (2018) highlighted that while probiotics and microbiome-targeting diets show some positive effects, these effects can be highly individual, with some people showing little to no improvement in health or weight. They suggest that the microbiome’s impact may be overstated in some cases.
Aron-Wisnewsky et al. (2019) also point out that while the gut microbiome plays a role in metabolic processes, other factors like genetics, social determinants of health, and lifestyle choices likely contribute more to an individual’s weight and health outcomes. This indicates that while the microbiome is part of the story, it’s not the full picture.

Beware the Snake-oil Sales Pitches!

In recent years, many diets, companies, and influencers have jumped on the microbiome bandwagon to promote fad diets, questionable tests, and health products, often making exaggerated claims about their effectiveness. You’ll see everything from expensive “gut cleansing” programmes to probiotic supplements and specialised foods that promise to “reset” or “balance” your microbiome for rapid weight loss or miraculous health benefits.

However, much of this marketing is not backed by solid scientific evidence. While the microbiome does play an important role in health, no single diet or supplement can instantly transform it or guarantee significant health improvements. Be cautious of buzzwords like “gut reset” or “detox,” and look out for products or plans that claim quick fixes without substantial research to support their claims. Instead, focus on balanced eating habits, and consult reliable sources or professionals before making drastic changes based on trendy microbiome claims.

It is hard when following some of these plans and diets to determine if they are really helping as, if you are eating better anyway, it is no real surprise that you are going to feel better!

Summary Number Two / CLosing ThougHts: So Does the Microbiome Really Matter?

In short, yes. Your microbiome does appear that it is an important player in your overall health, influencing everything from digestion and immunity to even your mood. While there’s still a lot to learn about the exact ways your gut bacteria impact your weight, it’s clear that maintaining a healthy and balanced diet which will also help your microbiome is a good step towards better health in general. Even if all the science turned out to be wrong, eating healthily is always a win regardless of whether you are doing it for your gut or not.

Again, none of this is intended as or should be used as medical advice. If you have a medical condition, always speak to a qualified healthcare professional.