Gut Microbiome and Obesity, Gut Dysbiosis and Metabolic Syndrome: Are They Linked?

Heather Campbell
 min read

A possible link between gut microbiome and obesity, dysbiosis and metabolic syndrome?

Gut Microbiome and Obesity, Gut Dysbiosis and Metabolic Syndrome: Are They Linked?An imbalance in our gut microbiota can lead to health problems. This can lead to intestinal dysbiosis, metabolic syndrome, and even obesity problems.

As a whole, the gut microbiome is made up of billions of bacteria that are beneficial in keeping our bodies healthy. Low microbiota diversity is associated with a high risk of abdominal obesity and thus gut dysbiosis and metabolic syndrome.

Medically, obesity can be defined as an excess of body fat that will lead to adverse health consequences and reduced life expectancy.

Continue reading to learn more about the link between our gut microbiome and obesity, dysbiosis and metabolic syndrome.

Gut microbiome and obesity: Introduction

Scientific research has recently concluded a probable role of the gut microbiota in the development of obesity, with some studies suggest that modulating the microbiota could help prevent this chronic disease.

Our gut microbiota is made up of billions of bacteria that can be beneficial in keeping our bodies healthy.

A parameter not to be neglected: the Body Mass Index

If we don’t consider our height, weight alone does not determine if a person’s build is average.

To know if a person is overweight or obese, the World Health Organization has adopted a tool called the Body Mass Index (BMI).

BMI is the ratio of weight (in kilos) to the square of height (meters). For example, if your weight is 132 pounds (60 kg) and your height is 5 feet and 3 inches (about 1.6 m), your body mass index will be calculated as follows:

  • the person’s weight (60 kg) divided by the square of the person’s height
  • the square of the person’s height in this example is 1.6 m x 1.6 m = 2.56 m²
  • BMI = 60 / 2.56 = 23.4 (kg/m²)

According to the World Health Organization, the ideal body mass index is between 18.5 and 25 kg per m². However:

  • A BMI of less than 16 is considered underweight
  • A BMI between 16.5 and 18.5 characterizes moderate to mild thinness
  • A BMI between 25 and 30 characterizes overweight
  • A BMI between 30 and 35 is deemed to be obese
  • A BMI between 35 and 40 is described as severe obesity
  • A BMI over 40 is considered morbidly obese.

BMI does not consider muscle mass, which can sometimes cause a high BMI without being overweight. Think of high-level sportsmen and women.

Apart from this exception, mortality in a population can vary with BMI.

The two main types of obesity

Around the 1970s, endocrinologists identified two main types of obesity found in both sexes: android obesity, more common in men, and gynoid obesity, more common in women.

Android obesity

Also called visceral obesity or abdominal obesity, this type of obesity is characterized by a strong intra-abdominal fatty overload giving an apple-shaped profile responsible for an increase in the abdominal perimeter.

Some individuals have excess abdominal fat without significantly increasing their body mass index.

These individuals are also at risk for the complications of abdominal obesity. Complications usually occur at a waist size of more than 3 feet in men and more than 2 feet 7 inches in women.

Gynoid obesity

Characterized by increased subcutaneous fat in the lower body (especially in the buttocks and thighs) and results in a pear-shaped profile, gynoid obesity is associated with a ratio of abdominal circumference to hip circumference and is much less dangerous to health than abdominal obesity.

A mysterious bacterium that protects us from abdominal obesity

Research in nearly 3,500 twins has shown that genetic makeup plays a significant role in the risk of abdominal obesity.

Genetic characteristics modify the risk of abdominal obesity by acting on the intestinal microbiota composition, which is independent of the body mass index.

This result suggests that studies on the links between microbiota and obesity complications should not only take into account the body mass index, but also consider excess abdominal fat, which is strongly linked to the risk of cardiovascular disease.

In these studies, low microbiota diversity was associated with a high risk of abdominal obesity. In addition, numerous bacteria that protect or increase the risk of abdominal obesity have been identified.

Among these bacteria, Blautia is related to the risk of abdominal obesity. On the contrary, the Oscillospira bacterium is a very protective bacterium against it.

The mechanisms involved in this protective effect are difficult to study because Oscillospira could not yet be grown in the laboratory.

The study of the metabolic capacities of the microbiota showed that abdominal obesity was therefore associated with bacteria capable of transforming fatty acids into sugar. These bacteria are responsible for insulin resistance and diabetes.

Hence the link between gut microbiome and obesity, gut dysbiosis and metabolic syndrome

Abdominal obesity puts you at risk for metabolic syndrome

Metabolic syndrome can be defined by at least three of the following abnormalities:

  • Abdominal circumference greater than 3 feet for men and 2 feet 7 inches for women
  • An increase in triglycerides
  • Low levels of HDL cholesterol (the good cholesterol)
  • High blood pressure
  • An increase in blood sugar levels on an empty stomach.

Metabolic syndrome, which may be caused by fructose, is associated with many complications such as diabetes, cardiovascular complications, cancers, etc.


Diabetes is defined as hyperglycemia, which is an increase in the concentration of sugar (glucose) in the blood. There are two main types of diabetes:

Type 1 diabetes

This type of diabetes is due to a lack of insulin, a hormone secreted by the pancreas to bring glucose into the body’s cells.

Affecting young people, this results from the destruction of the cells of the pancreas that produce insulin by the patient’s own immunity.

Treatment is by way of daily insulin injections.

Type 2 diabetes

This type of diabetes has a very different mechanism that usually complicates overweight or obesity. It is due to a resistance to the action of insulin of specific body cells (such as the fat cells of the fatty tissue, the muscle cells, or the liver cells).

Insulin resistance is observed under normal conditions during specific periods of life (such as adolescence, pregnancy, or old age). However, it does not usually have consequences, except during pregnancy with a risk of gestational diabetes.

Often, insulin resistance is abnormal and largely an indirect consequence of inflammation, which can be common during obesity.

In an attempt to reduce the increase in blood sugar, the beta cells of the pancreas increase their secretion of insulin, which increases the concentration in the blood.

Treatment of type 2 diabetes involves treating the causes of insulin resistance (such as being overweight, dietary errors, or lack of exercise) and attempting to reduce blood glucose and insulin resistance with insulin-sensitizing drugs.

Eventually, if these measures fail, the beta cells will become depleted, and insulin treatment will become necessary, as in type 1 diabetes.

Complications of metabolic syndrome outside of diabetes

In addition to diabetes, abdominal obesity and metabolic syndrome may also put the patient at high risk for fatty liver disease and cardiovascular complications, particularly myocardial infarction and stroke.

Metabolic syndrome is also associated with an increased risk of cancer, especially uterus cancers, postmenopausal breast, esophagus, colon, liver, kidney, and prostate.

What are the causes of abdominal obesity and metabolic syndrome?

Apart from rare cases of genetic origin, the causes of abdominal obesity and metabolic syndrome are often related to high dietary caloric intake and lack of physical activity.

However, certain toxins and the gut microbiota may also play an important role.

The link between Gut Microbiome and Obesity, Gut Dysbiosis and Metabolic Syndrome

Currently, studies have revealed a relationship between the composition of the gut microbiota and weight regulation mechanisms.

Indeed, in humans, the dysbiosis reported in cases of obesity is characterized by:

  • a decrease in the biodiversity of the microbiota,
  • a decrease in the phylum Bacteroidetes, and
  • an increase in the phylum Firmicutes.

Dysbiosis is associated with an increase in the permeability of the digestive wall, which will be responsible for inflammation.

Compared to people with a normal weight, the intestinal flora of obese people has a high fermentation capacity. In practice, this translates into an increase in the production of short-chain fatty acids and increased energy intake.

Excess energy is stored as fat. By acting on certain enzymes, bacteria belonging to the Firmicutes family increase fat storage in the body, thus aggravating overweight.

Suppose the loss of diversity of the intestinal flora is one of the characteristics of the microbiota of obese people. In that case, it is complicated to precisely characterize a profile of microbiota “obesity and metabolic disorders” based on the distribution of the various bacterial species.

On the other hand, the metabolic capacities of the microbiota in obese people are very different from those of the microbiota of slim people, and it is undoubtedly in this direction that the subsequent research will be directed.

Obesity and toxic substances

Benzopyrene is a chemical substance (polycyclic aromatic hydrocarbon) produced by incomplete combustion and it can be found in car exhaust, cigarette smoke, or smoke from a fireplace.

According to some experimental research, benzopyrene caused significant weight gain in rodents as benzopyrene slows down the use of fatty tissue stored by the body.

In fact, stored fats are much less mobilizable, and stocks are constantly increasing to the detriment of the figure.

However, the impact of toxic products on weight gain in humans is not yet well known. Cadmium exposure has been blamed for the occurrence of insulin resistance and diabetes.

Other studies on the risks of exposure to endocrine disruptors in children sometimes give contradictory results. Still, it looks pretty likely that maternal exposure during pregnancy could increase the risk of obesity in the child.

In addition, children of smoking mothers have an increased risk of obesity and metabolic disorders.

Diet and overweight

Knowing that there is a relationship between diet and overweight, here are some nutritional tips that can reduce caloric intake and improve the quality of the intestinal microbiota.

Measures that can help reduce caloric intake

There are several steps you can take to reduce your caloric intake:

  • Eliminate or reduce high energy foods such as pastries, sweets, processed foods, deli meats, fried foods, fats and oils, and sweetened beverages.
  • Limit your consumption of meat, eggs, bread, and cheese.
  • Take the time to chew your food thoroughly.
  • Avoid snacking between meals, which should be limited to three per day.
  • Get enough sleep.
  • Get enough physical activity.

Measures to improve the quality of the microbiota

Eat more fiber as found in various types of fiber such as fruits, vegetables, legumes, and whole grains.

Intake of saturated fats, pre packed meals and consumption of alcoholic beverages should be limited.

Targeting the microbiota to try to improve the effectiveness of weight-loss diets

A diet high in protein but low in fiber changes the composition of the microbiota.

This is characterized by a decrease in the digestion capacity of fibers and a decrease in the production of high-energy short-chain fatty acids. This likely reduces weight regain after weight loss.

In cases of overweight or obesity, people with a less rich and less diverse microbiota suffer more often from inflammation and metabolic complications than people with a rich and diverse microbiota.

Increased stool salinity may play a vital role in losing diversity of the gut microbiota and in the weight gain of ill individuals.

In particular, it is associated with a decrease in two protective bacteria of the intestinal barrier that have anti-inflammatory properties and reduce insulin resistance: the bacteria Bifidobacterium and Akkermansia muciniphila.

The effectiveness of weight-loss diets is undoubtedly linked to the metabolic capacities of the intestinal microbiota.

The more significant these capacities are, the more the digestive flora can draw large quantities of energy from the food, and the less effective the weight-loss diet will be.

According to some studies, the initial composition of the microbiota should be an essential element in managing patients with obesity.

Probiotics and prebiotics in the treatment of obesity and metabolic syndrome

One of the roles of pro or prebiotics is to restore the impermeability of the intestinal barrier when altered.

This stops chronic inflammation at the origin of insulin resistance and diabetes which is responsible in the long run for the most severe cardiovascular complications of metabolic disorders.

Experimental data


Akkermansia muciniphila is a bacterium with a reduced population in animals and obese humans with type 2 diabetes.

This probiotic, when administered to animals on a high-fat diet, reduced weight gain and the accumulation of abdominal and subcutaneous fat and reduced insulin resistance and inflammation.

The mechanism of this protective action is linked to the reinforcement of the intestinal barrier (by increasing the thickness of the mucus layer) and the intestinal immune defenses.

Akkermansia muciniphila, is one of the many beneficial endotoxin-producing bacteria in our intestinal microbiota.

Given the harmful role of intestinal translocation of endotoxins in obesity, it was necessary to ensure its safety before considering its use as a probiotic.

For this, studies have tested two states of the bacteria as probiotics: live bacteria and bacteria inactivated by pasteurization and neither resulted in significant adverse effects.

A preliminary study evaluated the tolerance and metabolic effects of daily oral administration of 10 billion Akkermansia muciniphila for three months in overweight volunteers with insulin resistance.

These volunteers were randomly selected to receive either a placebo, the live probiotic, or the pasteurized probiotic.

This trial showed that the pasteurized form is at least as effective as the live form and that both forms of the probiotic reduce insulin resistance and inflammation related to bacterial translocation.

A limited weight loss of just over 4 pounds was observed with the pasteurized form.

Experimentally, another probiotic could also be interesting in managing obesity and metabolic disorders: Lactobacillus rhamnosus.

It would reduce the proliferation of another bacterium, Bilophila wadsworthia, which is responsible for altering the intestinal wall, inflammation, and metabolic disorders. These adverse health effects are corrected with this probiotic.

Related postProbiotics Side Effects: Undesirable Things You Might Experience


The polyphenols (antioxidants) in Oolong tea, a Chinese tea without bitterness considered intermediate between green and black tea, behave like a prebiotic.

Given to obese rodents on a high-fat diet, polyphenols increase the biodiversity of their microbiota, thus correcting the dysbiosis induced by excess dietary fat.

However, what is vital in obesity and metabolic disorders is more the metabolic capacity of the microbiota than its bacterial composition.

Galacto-oligosaccharide prebiotics reduce the metabolic capacity of the microbiota in animals, thus reducing the production by bacteria of many substances, including fatty acids.

Some researchers believe that changes in the gut flora, induced by specific prebiotics, may improve obesity-related metabolic syndrome by reducing gut bacteria’s production of energy-producing substances, further establishing the link between gut microbiome and obesity.

Tip: If you’d like to learn more about gut bacteria and their impact on our health, check our other article Benefits of Gut Bacteria and Their Surprising Role in Human Health

Bariatric surgery and microbiota

Bariatric surgery aims to restrict food intake to reduce caloric intake and allow weight loss difficult to achieve through dietary measures alone.

There are two main types of surgery that are currently performed:

  • The first interventions consist of reducing the stomach volume either by implanting a ring around it or by removing part of the stomach to reduce it to a narrow tube.
  • The second type of surgery combines a resection of part of the stomach with a short-circuit of the first part of the small intestine (called a “bypass”). This reduces the stomach volume and the surface area of intestinal absorption of food.

When the indication for surgery is well supervised by a specialized multidisciplinary team, including surgeons, nutritionists, and psychologists, bariatric surgery results are very good.

These results inlcude an average weight loss of about 20 pounds, improved metabolic disorders and especially of insulin resistance and diabetes, an increase in life expectancy, and a marked decrease in the risk of obesity related cancers.

Changes in the gut microbiota post surgery have also been reported. These changes may play a role in weight stabilization after surgery because the initial dysbiosis is corrected. Hence a further link between gut microbiome and obesity.

Fecal transplantation and treatment of obesity and metabolic syndrome

Studies have shown that fecal transplantation does not lead to weight loss, but decreases insulin resistance in obese patients. Unfortunately, this was not maintained beyond five months.

There isn’t much research showing the link between fecal transplantation and obesity problems.

Gut microbiome and obesity: Conclusion

Consuming probiotics and prebiotics can play a role in rebalancing our microbiota, and we have explained the links between gut microbiome and obesity.

The BMI developed by the World Health Organization will show if you are overweight or obese.

And finally, it is essential to adopt a healthy lifestyle by having a balanced diet and practicing regular physical activity to avoid any risk of obesity, metabolic syndrome, or intestinal dysbiosis.

About Heather Campbell

As a nutritionist, my field of specialization is science-based nutritional advice but more importantly, it is my goal to share capturing and inspiring stories, examples and solutions which can help plus-size individuals overcome their specific difficulties. Read More