What is a Healthy Gut Microbiome and How Can I Get One?

As discussed in detail in my book The Mind-Gut Immune Connection and in many of my communications, the gut microbiome — the trillions of bacteria, viruses, and other microbes living inside our intestines help digest food, train the immune system, produce important metabolites, and send chemical signals throughout the body including the brain.

Studies have also shown that the gut microbiome responds rapidly to what we eat. Fiber-rich plant foods nourish a group of beneficial bacteria that produce short-chain fatty acids including butyrate, compounds known to reduce inflammation and improve insulin sensitivity. Reduced dietary fiber intake and highly processed foods, high in sugar, salt and added chemicals on the other hand, tend to encourage microbes associated with maladaptive immune system activation and metabolic dysfunction.

“Typical answers to what a healthy microbiome is usually list microbial diversity and richness, and a high prevalence of butyrate producers.”

Until now, most studies examining these relationships were relatively small or focused on a single population. This made it difficult to identify universal patterns or define what a “healthy” microbiome actually looks like. Typical answers to what a healthy microbiome is usually list microbial diversity and richness, and a high prevalence of butyrate producers.

A large new international study, recently published in the prestigious journal Nature by an international group of investigators under the lead of Francesco Asnicar has taken this idea further than ever before. By analyzing gut microbiome data from more than 34,000 people in the United States and the United Kingdom, researchers have created one of the most detailed maps to date linking diet, gut microbes, and human health. Their findings suggest that certain gut bacteria are consistently associated with better metabolic health, while others are linked to obesity and chronic disease — and that dietary changes can reliably shift the balance in a healthier direction.

Heart disease, type 2 diabetes, and related metabolic conditions — collectively known as cardiometabolic diseases — are now the leading causes of illness and death in many Western countries. These diseases are part of the non-contagious disease epidemic that has been unfolding over the past 75 years. It is generally agreed that the rise of ultra-processed foods, excess sugar, and low-fiber diets together with other lifestyle factors such as greatly reduced physical exercise have played a major role.

[Conventional medical tests] …don’t explain why two people eating similar diets can have very different health outcomes — or why the same diet works well for one person and poorly for another.

The medical system relies on commonly used measures such as body mass index (BMI), blood glucose, HgA1C, cholesterol, triglycerides, and inflammation to assess risk. These numbers are useful, but they don’t tell the whole story. For example, they don’t explain why two people eating similar diets can have very different health outcomes — or why the same diet works well for one person and poorly for another.

The new study by Asnicar and colleagues overcame this limitation by pooling data from five large cohorts, combining genetic sequencing of gut microbes with detailed dietary records, body measurements, blood tests, and metabolic markers. Advanced machine-learning tools were used to detect consistent patterns across countries, ages, and lifestyles.

One of the most innovative outcomes of this research was the creation of a microbiome health ranking. Instead of focusing on a single “good” or “bad” bacterium, the researchers evaluated 661 common gut microbial species and ranked them according to how strongly they were associated with favorable or unfavorable health markers. These included body fat, blood sugar control, cholesterol levels, inflammation, and post-meal metabolic responses.

The results showed two groups of microbes:

1. A group of favorable microbes were linked to lower BMI, better glucose control, healthier cholesterol profiles, and less inflammation.
2. A group of unfavorable microbes which were associated with obesity, insulin resistance, and cardiometabolic disease.

Importantly, many of the most beneficial microbes identified were poorly studied or previously unknown, highlighting how much we still have to learn about our inner ecosystem.

…the microbiome species associated with healthy diets overlapped strongly with those associated with good metabolic health.

The researchers also created a separate ranking based purely on diet quality, using well-validated dietary scores. Diets rich in whole, minimally processed plant foods consistently aligned with healthier microbiome profiles.

Not surprisingly, the microbiome species associated with healthy diets overlapped strongly with those associated with good metabolic health. This reinforces the idea that diet influences health in part by shaping the microbiome, rather than acting directly on the body alone.

However, the study also revealed some unexpected findings. Some bacteria were able to thrive even on less healthy diets while still producing beneficial compounds. This helps explain why people can respond differently to the same foods — and why nutrition is rarely one-size-fits-all.

“…researchers could often distinguish between healthy-weight and obese individuals based solely on their gut microbiome composition.”

Across multiple populations and independent datasets, people with lower BMI consistently carried more beneficial gut microbes, while people with obesity carried higher levels of unfavorable species. These patterns were strong enough that researchers could often distinguish between healthy-weight and obese individuals based solely on their gut microbiome composition. Even more compelling, these associations held up across countries and datasets, suggesting they reflect general biological signals, not cultural or geographic influences.

Microbiome Patterns and Disease

The researchers extended their analysis to people with other medical conditions which are part of the non-contagious disease epidemic, including type 2 diabetes, cardiovascular disease, inflammatory bowel disease, and colorectal cancer. Low grade engagement of the immune system has been implicated as a risk factor for all these diseases.

Once again, individuals without disease carried more favorable microbiome species, while those with disease had higher levels of unfavorable ones. Type 2 diabetes showed the strongest signal, reinforcing the microbiome’s important role in glucose regulation and insulin sensitivity.

Importantly, traditional measures of a healthy gut microbiome such as “microbial diversity” were less informative than this targeted ranking approach. It wasn’t just about having more different species of microbes — it was about having the right ones.

Can Diet Really Change the Microbiome?

There are a large number of studies often published in high impact journals which have shown an association between dietary patterns, the gut microbiome and health. However, such observational studies are powerful, but they don’t prove cause and effect. To address this, the researchers analyzed data from two dietary intervention trials.

In one study, participants followed a personalized, microbiome-informed nutrition program. In another, participants consumed a defined prebiotic fiber blend. In both cases, the results were clear:

• Beneficial microbes increased
• Unfavorable microbes decreased
• Metabolic health markers improved in parallel

The bacteria that increased were precisely those ranked as favorable in the large population studies — strong evidence that the rankings are meaningful and actionable.

What This Means for You

This research does not suggest that no matter what amount (how many colony forming units, or CFUs) of a single probiotic, or which “superfood” or supplement you take will fix metabolic health. Instead, it points toward a systems biological understanding of health. In such a view health emerges from patterns — of diet, microbes, and metabolism working together.

A diet rich in diverse plant foods, fiber, and minimally processed ingredients supports a gut ecosystem that, in turn, minimizes maladaptive immune system activation and supports metabolic resilience. Over time, this can reduce systemic inflammation, stabilize blood sugar, and lower disease risk.

The study also supports the growing idea of precision nutrition — using individual biology, including the microbiome, to guide dietary recommendations rather than relying on generic advice.

In the future, understanding your gut microbes may become as routine as checking your cholesterol — and far more informative about how food truly affects your body.

Perhaps the most important takeaway is this: the gut microbiome is not fixed. It responds predictably to dietary change, and those changes matter for health.

By providing a clear, evidence-based way to interpret microbiome data, this research opens the door to more personalized, effective strategies for preventing and managing cardiometabolic and several other chronic diseases.

For more details about this study, please keep an eye out for my upcoming podcast episode with Dr. Tim Spector, one of the senior authors of the paper. Episode coming next week (1/20/2026).