Could The Increase In Autoimmune Diseases Be Related To The Increase In Processed Foods?

It is well documented that there has been an increase in auto-immune diseases over the last three decades. Epidemiological data provides strong evidence that autoimmune diseases are definitely on the rise throughout westernized societies. Autoimmune diseases such as multiple sclerosis, type 1 diabetes, Crohn's disease, systemic lupus erythematosus, primary biliary cirrhosis, myasthenia gravis, autoimmune thyroiditis, hepatitis and rheumatic disease, bullous pemphigoid, and celiac disease are examples.

The increased incidence of autoimmune diseases is a world-wide trend but is seen mainly in western countries. During this period there has also been an increase in the amount of processed foods available for sale, particularly in western countries.  Living in westernized countries has a significant influence on nutritional intake. The “Western diet” includes regular consumption of high fat, trans fatty acids, cholesterol, proteins, sugars, salt intake, as well as the regular consumption of processed and fast-foods. 

Major shifts in dietary patterns are continually occurring. In fact, some studies have shown that the contribution of ultra-processed food to total household diet has increased by about 50% over recent years, and has replaced the intake of unprocessed and minimally processed foods. Whilst because of socioeconomic conditions this is happening more in western countries, it is a world-wide process is happening in both developing as well as in developed countries.

It is thought that this increase in autoimmune diseases is caused by some sort of environmental impact rather than genetic factors. The two major environmental factors thought to play a role in the development of autoimmune diseases are infections and nutrition. When you consider the geo-epidemiological distribution of autoimmune diseases - the world-wide North–south and West–east gradients in Europe, their relationship to socioeconomic status, their rapid increase in developed countries and observations in migrant populations it is understandable that scientist believe that environmental factors are driving these recent and rapid evolutionary changes.

So is there a link between auto immune disease and processed foods? Could the use of industrial food additives explain the rising incidence of autoimmune diseases?

The intestinal epithelial barrier consists of an intercellular tight junction which controls the equilibrium between tolerance of a particular food and immunity to non-self-antigens. It is well known that tight junction dysfunction is common in many autoimmune diseases, where the body forms abnormal antibodies against self-antigens. This link is understandable when you think that only a single layer of epithelial cells separates the gut contents from the layer of immune cells in the intestinal wall which are responsible for the production of antibodies. If this single layer of protective epithelial cells is breached, it can lead to pathological exposure of the highly immune-reactive sub-epithelium, to the large number of foreign antigens found in our food.

The tight junctions in our intestine have multiple roles. They are dynamic structures that are involved in developmental, physiological and pathological processes in the gut. Via a barrier mechanism, they control the movement of fluid, macromolecules and leukocytes from the intestinal lumen to the blood stream and vice versa. They protect the epithelial cells of the intestine against colonization by microorganisms. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, the tight junction also controls the equilibrium between tolerance and immunity to non-self-antigens and therefore they control the development of allergic responses and autoimmune responses to food.

It is not surprising, therefore, that if the function of the tight junction is affected, the physiological state of epithelial and/or endothelial cells is dramatically changed as well. Tight junction dysfunction seems to be a primary defect in people who have autoimmune diseases such as ulcerative colitis, Crohn's disease, celiac disease, inflammatory joint disease, ankylosing spondylitis, juvenile onset arthritis, psoriatic arthritis, type 1 diabetes mellitus and primary biliary cirrhosis. It is thought that in addition to genetic predisposition, the loss of the protective function of mucosal barriers that interact with the gut is necessary for autoimmunity to develop.

One hypothesis put forward in an article in Science Direct suggests that commonly used industrial food additives could cause some sort of dysfunction in the tight junction which allows leakage from the gut into the bloodstream.  The article suggests that food additives such as glucose, salt, emulsifiers, organic solvents, gluten, microbial transglutaminase, and nanoparticles which are extensively and increasingly used by the food industry may improve the qualities of food, but they may also increase intestinal permeability by breaching the integrity of tight junction paracellular transfer. This increased intestinal permeability through the opened tight junction, could therefore result in the entry of foreign immunogenic antigens such as gluten and activation of the autoimmune cascade.

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So far there are seven food additives which when ingested regularly in large amounts, are known to induce or which are associated with increased intestinal permeability:

1. Sugars (eg glucose)
2. Salt
3.  Emulsifiers and Surfactants
4. Organic Solvents (eg ethanol)
5.  Microbial transglutaminase (mTG). Transglutaminase is an extracellular enzyme and is biosynthesized by several microbes which is a very useful tool for modifying the functionality of proteins in food products.
6. Gluten
7.  Nanoparticles. Due to their unique properties and surface characteristics, can protect drugs from the destructive factors in the GI tract and can increase the permeability of macromolecules through the gastrointestinal barrier. 

Many of these additives can be combined, thus potentially combining their effect on tight junction permeability.

Summary

The diet of the industrialized and urbanized parts of the world today is vastly different from what it was even two or three decades ago, with a whole new range of processed and fast food experiences, which rely of food additives to improve taste and quality. There is also a number of genetically modified crops in use which this article has not addressed. Over recent decades, a significant increase in the incidence of autoimmune diseases in western and other industrialized countries has led to the hypotheses that diet is a potential environmental risk factor for such disorders. This article in the Science Direct http://www.sciencedirect.com/science/article/pii/S1568997215000245   has not definitively proven this link, evidence shows that increases in the usage of the abovementioned food additives have paralleled increased incidences and prevalence of autoimmune diseases during the last decades, as evidenced in the figure below. Where A and B (r2 = 0.9829, 0.886, respectively).

The parallel net increase % per year in various countries of: A. Food additives usage and B. AD frequencies over the last decades. Source Science Direct 

The confirmed facts are, however: 

1. Incidence of autoimmune diseases and food additive consumption is increasing.
2.  Commonly used industrial food additives enhance intestinal junction leakage.
3.  Glucose, salt, emulsifier, gluten, microbial mTG, nanoparticle increase tight junction leakage.

It is easy to conclude, therefore, that the intestinal entry of foreign antigens due to increased tight junction permeability could be caused by the increased of food additives found in processed foods. In turn this could activate the autoimmune cascade which could indeed lead you to believe that the increase in autoimmune diseases is definitely related to the increase in processed foods. However, further research on food additives exposure causing intestinal permeability leading to autoimmune diseases is required to clarify our understanding of the common mechanisms associated with the causes of autoimmune diseases.

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