The Microbiome, Metabolism & Inflammation
We usually think of metabolic health in terms of blood glucose, insulin, cholesterol, and body weight.
But researchers are discovering that the microorganisms living in our intestines may also influence metabolism and inflammation.
The gut microbiome may play an important role in metabolic health, although much of the research is still developing.
The Microbiome and Insulin Resistance
Studies have found differences in gut bacteria between people with insulin resistance or type 2 diabetes and those with normal blood glucose regulation.
Some microorganisms produce substances that influence insulin signaling, while others interact with the immune system.
However, most human studies have been observational.
We cannot assume that differences in gut bacteria cause insulin resistance simply because the two are associated.
Short-Chain Fatty Acids
Certain intestinal bacteria ferment dietary fiber and produce substances called short-chain fatty acids, including acetate, propionate, and butyrate.
Butyrate helps nourish cells lining the colon and supports the intestinal barrier.
These substances may also influence appetite, glucose metabolism, and immune function.
Animal studies have demonstrated interesting metabolic effects, but the benefits in humans are less certain.
The Microbiome and Inflammation
The intestinal lining helps prevent unwanted substances from entering the bloodstream.
Researchers are investigating whether changes in gut bacteria and the intestinal barrier contribute to chronic low-grade inflammation.
One proposed mechanism involves bacterial components that can stimulate immune responses.
This may help explain connections between the microbiome, obesity, and insulin resistance.
See CRP & hs-CRP: Understanding Inflammation Tests for more about how blood tests can help identify inflammation in the body.
However, much of the evidence comes from animal studies, and the importance of these mechanisms in humans remains uncertain.
Diet and the Microbiome
Diet can change the composition and activity of intestinal microorganisms, sometimes within days.
Different bacteria thrive on different nutrients, particularly dietary fibers and other plant compounds.
For people following low-carbohydrate diets, vegetables, nuts, seeds, and other fiber-containing foods can help support microbial activity.
Some studies have found changes in fiber-fermenting bacteria during very-low-carbohydrate diets, but their long-term health implications remain unclear.
There is insufficient evidence that low-carbohydrate diets are inherently beneficial or harmful to the microbiome.
Prebiotics and Probiotics
Prebiotics are substances that beneficial microorganisms can use, producing a health benefit.
Many are types of dietary fiber found in foods such as onions, garlic, asparagus, and artichokes. Some are available as supplements.
Probiotics are live microorganisms that provide a demonstrated health benefit when consumed in adequate amounts.
Certain probiotics have shown modest improvements in blood glucose or inflammatory markers in clinical trials, but results vary.
There is not enough evidence to recommend probiotics as a general treatment for insulin resistance or type 2 diabetes.
Fermented Foods
Fermented foods include yogurt, kefir, sauerkraut, kimchi, and certain cheeses.
Some contain living microorganisms, although not all fermented foods qualify as probiotics.
A 2021 Stanford clinical trial found that eating fermented foods increased gut microbial diversity and reduced several inflammatory markers.
More recent research has produced mixed results. A 2025 review found some benefits for digestive health, while a 2026 clinical trial of sauerkraut found little overall improvement in inflammation or blood glucose regulation.
Fermented foods may be a useful part of a healthy diet, but their ability to prevent metabolic diseases remains unproven.
What Does This Mean for Older Adults?
The microbiome changes as we age, and researchers are investigating connections with insulin resistance, inflammation, and frailty.
However, microbiome testing and supplements have not been shown to reliably prevent age-related metabolic decline.
For now, maintaining a nutritious diet, adequate protein intake, physical activity, and muscle strength remains more important than trying to achieve a particular microbiome profile.
See Exercise, Muscle Strength & Healthy Aging for more about maintaining strength, mobility, and independence as we age.
The microbiome adds an important dimension to our understanding of metabolic health, but it does not replace established approaches to maintaining it.
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Discusses yogurt, kefir, sauerkraut, and other fermented foods, including their possible benefits and limitations.
Explains probiotics, prebiotics, what clinical studies have found, and when supplements may be useful.