How a chain reaction in white fat cells aggravates obesity and related diseases

Gaining a little bit of weight can trigger more and more weight gain. No, we don't mean that you let go when you put on a little bit of fat around the belly, hips and arms. Instead, research has now shown that the body can fall into a vicious cycle of weight gain-inflammation-weight gain-disease.

Here's how: a complex chain reaction in a person's own fat cells has been linked to a disruption in metabolism and weak immune response, leading to an increased risk of diseases and infections, according to a new study based on research carried out by scientists at the Cincinnati Children’s Hospital Medical Center and the University of Cincinnati College of Medicine.

The research, which was published in the scientific journal Nature on 2 June, as “Type I interferon sensing unlocks dormant adipocyte inflammatory potential”, argues that when obesity occurs in a human body, the person's own fat cells set off a chain reaction that worsens the body's immune response against pathogens and infections including COVID-19, leading to poor outcomes in patients.

Past studies have worryingly highlighted the rising rate of obesity around the world, with a 2014 study published in the Lancet stating that nearly 30% of the world's population was either obese or overweight (about 13% of adults are obese according to a 2016 study). These latest findings, however, can help in understanding why.

How weight gain leads to more weight gain
Heightened health risks from obesity

How weight gain leads to more weight gain

The scientists found that a type of proteins produced by immune cells in the body, called type I interferons, are also generated by the fat cells in the body known as adipocytes. The interferons are responsible for a chronic immune response which takes place at a constant yet low state, but heightens the cycle of inflammation in the white adipose tissues (WAT). In other words, the constant presence of these proteins means that there is low-level inflammation in the white fat cells at all times.

White adipose tissue, or simply white fat, is one of the two types of adipose tissues in the body, the other being brown fat. It is this white adipose tissue that makes up 20-25% of an average human being's body weight. This white fat is the type of fat that expands to form the bulges that are seen on the belly, thighs as well as under the arms.

The resulting inflammation then drives a series of cellular responses and reactions that causes obesity-related illnesses in people, primarily type 2 diabetes as well as non-alcoholic fatty liver disease (NAFLD). (Read more: Fatty liver)

Fat distribution in the human body has long been an indicator of many illnesses including diabetes and heart disease. The new study goes on to show how type 1 interferons (IFN) interact with IFNa receptors that triggers a cycle of inflammation, which leads to changes in the expression of various genes that are linked to inflammation, fatty acid production as well as glycolysis in the body.

The study, which was conducted on mice, observed increases in various gene expressions, and many of the metabolic changes in mice were also found in human adipocytes. The researchers are investigating further to find out about the specific mechanisms of how type 1 interferons interact with adipocytes and how they impact metabolism. The scientists did not expect to find such an activity taking place in the body before, as type 1 interferons have only previously been studied in relation to viral infections and to study the functioning of immune cells in the body.

It goes to show how type 1 interferons specifically target adipocytes and modify their metabolic circuit, which according to the scientists has been observed for the first time.

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Heightened health risks from obesity

It is already well known that obesity affects a large section of the global population and is known to be a major risk factor behind diabetes, heart-related ailments as well as many types of cancer, besides being a risk factor for developing complications from various types of infections.

Obesity is one of the health conditions that put people at greater risk of severe illness if they catch the new coronavirus infection, COVID-19. And not just COVID-19, other infections like of H1N1 influenza also tend to be more severe, even lethal, among people who were obese.

Of course, previous studies done to understand obesity have already shown that it is not just caused by overeating or not being active enough. The complicated process of how the body breaks down nutrients from food and converts it into energy for the multitude of cells in the body is also a factor behind obesity.

Some scientists, however, have now begun to understand that the excess calories consumed by the body could be responsible for a change in how fat cells behave and affect the immune system as a result.