The Microbiome and Insulin Resistance

By Dr. Cathy Sevcik, ND

Advances in technology have facilitated an explosion of research and interest into the human microbiome.  What we know now is that the under ideal conditions the microbiome is a complex system of diverse entities that both compete and collaborate with each other and with our own cells to create an environment in which we all flourish.

This research is turning up abundant evidence that the microbiome’s role is central to the optimal (or on the flip side, dysfunctional) operation of most of our body’s systems.  We’re going to aim our attention at metabolic health and specifically at insulin resistance.  We’ll discuss an overview of what insulin resistance is, why it’s a problem, how the microbiome may be involved in its evolution and what we might be able to do about it.

What is Insulin Resistance and Why is it a Problem?

Insulin is well known as the hormone that facilitates glucose uptake into most cells in the body.  But it is also the main regulator of lipogenesis (making fat).  It is anabolic and helps us grow muscles.

Brain and liver cells don’t need insulin and this becomes hazardous to them when circulating glucose levels are too high for extended periods.

Most other cells, including muscle, can regulate their response to insulin and uptake of glucose.  When glucose storage depots in the liver and muscle are full of glycogen, they don’t respond as easily to the same level of insulin.  At this point the pancreas must release more insulin to clear blood glucose and this is called insulin resistance.   This process generates momentum over time.

Higher levels of insulin promote conversion of excess glucose to fat which accumulates in adipose tissue and, more dangerously, in the liver and pancreas.  Liver fat accumulation (Non-Alcoholic Fatty Liver Disease or NAFLD) can lead to declining liver function and worst-case scenario to cirrhosis, now the leading cause of liver transplants in the modern world.

Fat accumulation in the pancreas may eventually interfere with insulin production and secretion which ultimately could lead to the need for insulin replacement therapy.

Insulin resistance is now seen as the fork in the road between good health and the chronic degenerative diseases of the modern world (obesity, type 2 diabetes, cardiovascular disease, Alzheimer’s, NAFLD, cancer).  Weight gain around the abdomen is the hallmark of insulin resistance.  And it plays a role in why it is so much harder to lose weight as we age.

The Microbiome’s Role in Insulin Resistance

Because most of our microbiome can’t be cultured, studying it effectively required advancement in technology, such as RNA gene sequencing, which has been available for about 20 years.  The Human Microbiome Project is an initiative in which the NIH undertook to genetically sequence the microbiome of a sample of healthy lean individuals.  They have characterized a large number of organisms in the healthy microbiome including bacteria, yeasts and viruses.  That endeavor provided a database useful for comparing less healthy populations/individuals to ascertain the potential role of the microbiome in disease processes.

Our knowledge in this area is exploding but is also in its infancy.  Most of the research on humans compares microbiomes in healthy lean individuals versus obese insulin resistant individuals.  As result, we can’t conclude which came first, the insulin resistance or the microbiome changes.  Animal models can be manipulated to determine causal relationships but should be interpreted and generalized to humans cautiously.  Let’s look at what research has uncovered so far.

Microbiome composition alterations

Insulin resistant and obese individuals have different proportions of bacterial phyla as compared to lean, healthy individuals:  specifically higher Firmicutes and Actinobacteria compared to Bacteroidetes.  These alterations seem to have 2 primary affects:  low-grade inflammation and increased energy extraction.

Despite the fact that the above bacteria are part of normal healthy flora, the imbalance has been observed to lead to increased intestinal permeability and increased circulation of bacterial toxin called lipopolysaccharide (LPS).  LPS initiates a cascade that reduces insulin sensitivity.  More insulin must be produced to achieve the same effect, leading to weight gain.

Firmicutes increase energy extraction from dietary polysaccharides which has been shown to increase triglyceride formation in the liver and more deposition of fat in the liver and fat tissues.  Elevated serum triglycerides are frequently observed in insulin resistant individuals and is a marker of metabolic syndrome.

Actions to Improve Microbiome Composition and Insulin Sensitivity

Current protocols to improve insulin sensitivity focus on reducing dietary sugar and starchy carbohydrates in order to reduce insulin production.  Low carbohydrate-high fat and keto diets appear to be quite effective at achieving this and leading to weight loss.  But if the complex plant food consumption is too low, the microbiome may suffer and we don’t understand the long-term consequences of this.  Thus, it seems prudent to employ a number of tools to achieve our goals of metabolic health, weight loss and long-term vitality.

Microbiome testing is newly available that uses more advanced technology to assess diversity and composition compared to the healthy reference population.  This testing may become an essential tool in the process of solving patients’ health issues.

If you suspect or if you test and the ratio of Bacteroidetes to the other phyla is low, then consuming foods that will correct this imbalance could be helpful.  Bacteroidetes thrive on a diet of foods high in beta-glucans, resistant starches, arabinoxylan, pectin, cellulose, or inulin.  Always go slow when adding fibers to your diet as they can cause digestive disturbances.  Also, drink plenty of water to ensure that high fibre foods or prebiotic products don’t create an obstruction in your colon.

Do probiotics help?  That’s a good question.  Before you purchase a product, check to ensure that it has been specifically tested to help the condition you wish to treat.  Most probiotics on the market rely on research conducted on the species and strains but not on their specific product.  You have no assurance that the microbes can survive the trip from your mouth to your colon, where they need to grow.  Sometimes a product will contain strains that have not been tested to ensure that they are compatible with each other.  Probiotics don’t seem to have a lasting effect on the microbiome composition.

Fortunately, along with microbiome genome sequencing, probiotic technology is also advancing with products that contain spore strains that can regulate the colonic environment so that the desirable micro-biota can thrive.


  • Caricilli AM, Saad MJA. The Role of Gut Microbiota on Insulin Resistance. Nutrients. 2013; 5(3):829-851.
  • Dr Cathy Sevcik, ND practices at Westcoast Women’s clinic where she focusses on helping patients restore metabolic, immune and digestive health.