Scientists believe the growing popularity of Western-style diets is a major reason why autoimmune diseases are spiking globally.

With cases of the diseases-of which there are at least 100 different types-growing by between 3 percent and 9 percent a year, experts at the Francis Crick Institute in London, England wanted to know why.

James Lee, who is leading one research group at the institute, told The Observer newspaper: “Human genetics hasn’t altered over the past few decades. So, something must be changing in the outside world in a way that is increasing our predisposition to autoimmune disease.”

The team found Western-style diets heavy on processed ingredients and light on fresh vegetables were at the heart of the problem; causing autoimmune diseases that then confuse immune systems to the extent that they struggle to tell the difference between healthy cells and the viruses and bacteria they should be attacking.

The Times newspaper said the damaged immune systems often attack their hosts, and people with such diseases frequently develop ailments including rheumatoid arthritis, type 1 diabetes, celiac disease, lupus, inflammatory bowel disease, and multiple sclerosis.

Around 4 million people out of the United Kingdom’s 66 million inhabitants have an autoimmune disease.

The Times newspaper said the prevalence of the diseases increased quickly in the West around 40 years ago and is starting to do likewise in the Middle East and East Asia, where Western-style fast food has been growing in popularity.

Carola Vinuesa, who also heads a research team at the Francis Crick Institute, told The Times newspaper: “Fast-food diets lack certain important ingredients, such as fiber, and evidence suggests this alteration affects a person’s microbiome-the collection of microorganisms that we have in our gut and which play a key role in controlling various bodily functions.”

She said not everyone who eats a Western diet will develop an autoimmune disease but some people have “certain genetic susceptibilities” to do so.

“There is not a lot we can do to halt the global spread of fast-food franchises,” she said. “So, instead, we are trying to understand the fundamental genetic mechanisms that underpin autoimmune diseases and make some people susceptible but others not. We want to tackle the issue at that level.”

The teams at the Francis Crick Institute are hoping to develop targeted treatments for people with autoimmune diseases, but, with so many types of disease out there, they are also working on identifying the strains.

“We have to learn how to group and stratify patients, so we can give them the right therapy,” The Guardian newspaper quoted Vinuesa as saying.

The scientists are also trying to pinpoint tiny DNA differences among people, to see whether they can predict which individuals might be susceptible to developing an autoimmune disease, if exposed to a fast-food diet.