Diet and Gut Microbiota in Inflammation and Disease

Emerging evidence links chronic intestinal inflammation with obesity and metabolic disorders like insulin resistance.

What’s more, this association seems to be affected by changes in the gut microbiota caused by diet.

Recently, a group of researchers summarized the available evidence in a review published in Cell Metabolism. Below is an overview of the review’s main points.

Overweight Midsection of Woman

Article Reviewed

This article discusses the association of intestinal inflammation, obesity, metabolic syndrome, the gut microbiota and dietary factors.

The Intestinal Immune System in Obesity and Insulin Resistance.

What is Inflammation?

Inflammation is the immune system’s response to infection, injury or toxins. There are two types of inflammation: acute inflammation and chronic inflammation.

Acute inflammation

Acute inflammation starts immediately after an injury or infection.

Its purpose is to eliminate foreign substances or invaders, such as bacteria or viruses, as well as to remove dead or injured cells that are no longer functional.

Although it causes the swelling and redness associated with wounds and infections, it is an essential process that helps the body heal and protects it against further harm.

Chronic inflammation

Chronic inflammation lasts longer than acute inflammation. For this reason, it damages living tissue. This increases the risk of diseases like cancer, heart disease and type 2 diabetes.

Many conditions may lead to chronic inflammation, including infection, toxin exposure, autoimmune diseases, age, high blood sugar levels or an unhealthy diet.

Low-grade, chronic inflammation is an underlying condition in obesity, insulin resistance and many other conditions.

Bottom Line: There are two types of inflammation: acute and chronic. Acute inflammation is a beneficial process, while chronic inflammation is associated with obesity and metabolic diseases.

Obesity is Associated With Dysbiosis

Obesity and metabolic syndrome are associated with dysbiosis, a term that refers to an imbalance in the gut microbiota (1).

Some scientists even believe that dysbiosis plays a key role in the development of obesity.

This idea is supported by animal studies, showing that mice without any bacteria in their intestines had lower amounts of body fat, and did not become obese or insulin resistant when put on a high-fat diet.

However, when the intestines of these same mice were colonized by gut bacteria from normal mice, they started to gain fat and develop insulin resistance (23).

What’s more, intestinal bacteria from obese mice increased fat gain more than bacteria from lean mice (1).

Consistently, killing the intestinal bacteria of obese mice with an antibiotic treatment reduced body fat and improved insulin sensitivity (45).

However, obese people should not resort to taking antibiotics, as there are other, healthier approaches. Human studies have shown that weight loss may restore gut microbiota balance and improve metabolic health (67).

Bottom Line: Different types of bacteria are predominant in obese people’s guts. These bacteria make it easier for them to absorb calories and gain fat.

Dysbiosis May Cause Intestinal Inflammation

Studies indicate that obesity-associated dysbiosis may promote weight gain. This is because obese people may have greater numbers of bacteria that improve calorie absorption.

Dysbiosis also seems to be characterized by low numbers of beneficial, anti-inflammatory bacteria.

These bacteria feed on fiber, especially prebiotic fiber, and produce short-chain fatty acids like butyrate. Butyrate improves colon health and reduces inflammation.

For this reason, a lack of butyrate-producing bacteria may promote intestinal inflammation.

Transferring gut bacteria from lean, healthy donors to those with metabolic syndrome increased the butyrate-producing bacteria, which improved insulin sensitivity (8).

This also seems to be related to diet, in that obese people tend to have lower bacterial diversity and richness in their guts. However, one study showed that bacterial diversity can be restored by eating less (910).

Bottom Line: An imbalance in the microbiota of obese individuals may lead to intestinal inflammation. This imbalance is characterized by low numbers of beneficial, anti-inflammatory bacteria.

Dysbiosis May Weaken the Gut Wall

Intestinal permeability is an essential function of the gut wall. It allows nutrients to pass across the gut barrier into the blood circulation.

But the gut barrier should not be too permeable, since it needs to prevent potentially harmful substances from entering the body.

However, excessive intestinal permeability is an unfortunate consequence of dysbiosis and intestinal inflammation.

This leads to the leakage of bacteria or bacterial toxins across the gut barrier, worsening systemic inflammation and metabolic disease. This condition is called metabolic endotoxemia (41112).

Endotoxemia is associated with high calorie intake, high intake of saturated fat, abdominal obesity and an increased risk of diabetes (1314).

Conversely, getting enough fiber might help prevent endotoxemia by increasing the numbers of beneficial bacteria and strengthening the gut barrier (15).

Nevertheless, further studies are needed before any solid conclusions can be reached.

Bottom Line: Dysbiosis and intestinal inflammation may also increase intestinal permeability, allowing harmful substances to “leak” across the gut barrier. This may worsen inflammation and metabolic disorders.

Dietary Factors Affect Intestinal Inflammation

Intestinal inflammation is not only associated with dysbiosis and a “leaky gut.” All of this also appears to be linked to dietary habits.

Dietary factors that may worsen intestinal inflammation include:

  • A diet high in saturated fat: A diet high in saturated fat has been associated with intestinal inflammation in mice. This effect appears to be mediated by the gut microbiota, since bacteria-free mice showed no effects (161718).
  • Food emulsifiers: Another mouse study suggests that two commonly-used food emulsifiers may change the gut microbiota and worsen inflammation (19).

Other dietary factors may protect against inflammation:

  • Losing weight: One human study showed that losing weight reduced intestinal inflammation, while also improving blood sugar levels and blood lipids (20).
  • Omega-3 fatty acids: A study in mice found that saturated fats from lard increased inflammation, whereas polyunsaturated fats from fish oil protected against inflammation (16).
  • Probiotics: Several types of probiotic bacteria may reduce intestinal inflammation and strengthen the gut barrier (2122232425).
  • Antioxidants: Antioxidant polyphenols from fruits and vegetables may also reduce inflammation (26).
  • Prebiotic fiber: Eating plenty of prebiotic fiber encourages the growth of beneficial bacteria that produce anti-inflammatory short-chain fatty acids, such as butyrate (27).

Several studies have also examined the effects of anti-inflammatory drugs on intestinal inflammation and metabolic conditions.

Apart from reducing inflammation, anti-inflammatory drugs may improve insulin sensitivity, decrease fasting blood sugar, reduce endotoxemia and increase gut bacterial diversity, without any effects on body weight (282930).

Taken together, these findings support the idea that diet-induced inflammation plays a key role in the development of chronic diseases in obesity.

Bottom Line: Dietary factors may either worsen or improve intestinal inflammation. Many of these effects seem to be mediated by the gut microbiota.

Summary and Real-Life Application

Obesity and many metabolic disorders are associated with chronic intestinal inflammation. Dietary factors and the gut microbiota also play a key role.

Fortunately, dietary strategies may be able to prevent or reduce these problems. These strategies may also improve many obesity-related metabolic conditions, such as insulin resistance.

Effective strategies include losing weight, eating omega-3s, and taking prebiotic fiber and probiotics.