Western diet triggers immune responses usually associated with infection

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Author: Layal Liverpool Edited by: Isabel Wassing

A recent study links the Western diet to immune activation reminiscent of the body’s response to an infection. Mice fed a high fat, high carbohydrate diet displayed signs of excessive immune activation, which persisted even after they were returned to a normal, healthy diet. The researchers identified specific immune cells that are involved and observed similar long-term changes in human cells grown in the lab.

The Western diet

Invisible microorganisms like viruses and bacteria are no longer the biggest killers around. In western societies today, more than 80% of deaths are due to non-infectious diseases, such as obesity, type II diabetes and heart disease. While infectious diseases accounted for about half of all deaths in the late 1800s, this has now fallen to only 15%. (1)

In particular, western-type diets that promote the blockage of blood vessels by increasing circulating levels of so-called “bad” or LDL cholesterol have been linked to increased disease risk. It seems the new villains to look out for might be high calorie, high fat and high sugar diets rather than viruses and bacteria. But what are the mechanisms that underlie this?

Activating the immune system

Recent research has suggested that infectious diseases and Western diets have something in common; they can both activate our immune system in particular ways. In the context of unwelcomed virus or bacterium, this is a good thing. Alerted to the presence of an unwanted invader, the immune system sets into motion a series of powerful and highly coordinated responses to eliminate the infection from the body.

However, the same mechanisms that the immune system uses to damage the cells of microbes like bacteria, can also cause damage to healthy cells in the body. To avoid unwanted damage to healthy cells, activation of the immune system must be carefully controlled to prevent inappropriate responses to anything that is not really dangerous.

Recent research has revealed that the Western diet can activate immune responses in the absence of any pathogens . This excessive immune activation can damage healthy cells, contributing to disease.

The Western diet looks like an infection

Scientists at the University of Bonn in Germany fed laboratory mice a Western diet, which was low in protein and high in saturated fats and carbohydrates. After only one month on this new diet, the mice displayed multiple signs of inflammation and immune cell activation not normally seen in healthy mice. (2, 3)

When the mice were returned to a normal, healthy diet, some of the immune responses subsided, but others persisted long after the mice were switched back to their normal diet. A specific type of immune cell, which usually forms part of the early response to infection, remained highly activated even one month after the mice had returned to healthy food.

Immune cells never forget

Aside from their important role in eliminating infections, immune cells are also able to remember specific signatures of pathogens that the body has encountered before. This memory allows our immune system to activate a more powerful immune response against a foreign entity the second time around, thereby speedily eliminating the pathogen and stopping the spread of infection.

Similarly, the immune cells from the mice who consumed food based on a Western diet not only became activated, but “remembered” that they had been activated and remained switched-on even after the diet returned to normal. Epigenetics or chemical changes to specific genes in the immune cells are the root mechanisms of this process.

What does this mean for us?

The scientists observed similar epigenetic changes in human immune cells that were exposed to LDL - the “bad cholesterol” carrying molecule associated with the Western diet. This is quite concerning when we consider the possibility that certain epigenetic changes can be inherited (4). Could the negative effects of our poor diet be passed down to our children through these changes to our genes? Further research will be needed to investigate this possibility.

But it’s not all doom and gloom! In their study, the researchers also uncovered a key molecule responsible for alerting the immune cells to the Western diet. This molecule, with the catchy name NLRP3 (2) , represents an exciting potential target for future therapies.

Sources:

(1) Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980–2015: a systematic analysis for the Global Burden of Disease Study 2015 - https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)31012-1/fulltext

(2) Western Diet Triggers NLRP3-Dependent Innate Immune Reprogramming - https://t.co/8kNX0gBUgX 

(3) Unhealthy Diet Triggers Epigenetic Changes in Innate Immune System - https://www.genengnews.com/gen-news-highlights/unhealthy-diet-triggers-epigenetic-changes-in-innate-immune-system/81255368

(4) The Ghost in our Genes (BBC Horizon documentary) - http://www.bbc.co.uk/sn/tvradio/programmes/horizon/ghostgenes.shtml

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