In a nutshell, food components and additives in ‘Western diet’ actively change gut Microbiota – Wikipedia, apparently for the worse, not the better, which leads to inappropriate and/or inappropriately persisting inflammation. Since microbial antigens and metabolites can access the circulation and hence reach every part of the body, systemic, not local, adverse consequences such as Metabolic syndrome – Wikipedia ensue, and risk for diseases such as cancer increase as a consequence of the tilting of balance from health to disease during the inevitable trade-offs that are so much a part of the processes that define life, growth, survival and reproduction.
This answer briefly summarizes
- How proper understanding of inflammation is essential for understanding its role in human health.
- Definition of Western diet.
- Illustrative examples of how Western diet ingredients appear to negatively impact human gut microbiota.
Already a contested word in the immunology lexicon, no wonder once it seeped out, inflammation became one of the most misunderstood words in popular usage as well. Clarifications about inflammation are thus first necessary.
- One, inflammation is an essential part of normal immune system function.
- Two, inflammation is a process, not an outcome.
Inflammation becomes a problem when the body inappropriately activates, inappropriately manages and/or inappropriately allows it to persist, all of which occur as a result of underlying physiological problems.
Accidentally cut a finger with a knife, inflammation is a necessary part of the healing process. If the body manages this healing process inappropriately as a consequence of underlying health problems (e.g., diabetes), the wound could get infected, forcing other types of inflammatory mediators to get engaged, the process might persist longer than is beneficial and the infection might even spread, leading to even more serious health consequences.
Rather than a problem itself, inappropriate or inappropriately persisting inflammation is more a beacon indicating underlying health problems. In the case of diet-associated inflammation, the underlying issue is how diets shape gut microbiota and the consequences thereof.
Absent specific context, the overused marketing cliche, ‘anti-inflammatory!’, that overwhelms so much of advertising is pretty much hot air, especially when used in isolation in service of a single or few ingredients. Diets rather than individual ingredients enhance or diminish propensity for persistent inflammation.
In a sign that bad habits also tend to be among the most addictive (1), even as the phrase ‘Western diet’ has taken on the attributes of a four-letter word in recent years, it only seems to globalize, relentlessly marching onward year on year colonizing country after country, Chile (2), India (3), Malaysia (4), Mexico (5), the list goes on.
Rather than inevitable, much of this unsound status quo is the outcome of lifestyle changes that increasingly prioritize convenience getting yoked to relentless, careful, decades-long, carpet-bombing type of marketing by the food industry even as the broad tacit overlap between this industry’s goals and economic considerations of policy makers helps further cement its business model. That US hospital food is largely processed is irony personified and a sign of the extent to which processed food permeates American culture, presumably with the population’s tacit if not overt acquiescence.
Convenience, shelf-life, resistance to spoilage its chief hallmarks, Western diet is today used as a short hand for food with
- A surfeit of empty calories (sugar and alcohol).
- High in total, saturated and animal fat.
- Low in complex carbohydrates and dietary fiber.
In practical terms, lot of red meat, especially processed meat, refined grains, high-fat dairy, a variety of highly processed foods, drinks and sweets with a lot of added sugar and any number of food additives (preservatives, dietary emulsifiers, Thickening agent – Wikipedia, Leavening agent – Wikipedia, artificial sweeteners and the like) euphemistically deemed Generally recognized as safe – Wikipedia (GRAS) while being low in whole grains, fruits and vegetables (see below from 6).
How Western diet Ingredients Appear Problematic: Negative Impact on Human Gut Microbiota
The illustrative example of GRAS ingredients helps reveal how Western diets tend to be harmful in the long run.
Largely ignorant of the importance of microbiota and how our diets influence them, the modern food industry assembled itself over the course of the 20th century, using the GRAS loophole to exponentially expand the ingredients it adds to processed foods to enhance certain flavors, tastes, and textures, and to prolong shelf-life and stability (see below from 7).
‘In the past five decades, the number of food additives has skyrocketed — from about 800 to more than 10,000. They are added to everything from baked goods and breakfast cereals to energy bars and carbonated drinks.’
The food industry’s rules of thumb regarding nutritive value and safety of various foodstuffs may have been wholly inadequate to the task at hand simply because knowledge of the importance and influence of microbiota didn’t emerge in mainstream science until the 2000s and such research increasingly reveals how the diets we consume actively shape the microbes that inhabit our GI tracts.
A heavy reliance on GRAS food components is emblematic of Western diets. Analyze at random the ingredient list of some packaged food and inevitably one or more of polysaccharides such as Carboxymethyl cellulose, carrageenan, maltodextrin, soy lecithin, pectin, polysorbate 80, xanthan gum is sure to pop up while non-nutritive sweeteners are pervasive in beverages and baked goods (see some examples below from 8).
An illustrative example of how GRAS entails a lot more than meets the eye, as an immunologist, my first introduction to Carrageenan – Wikipedia was not as a food ingredient deemed GRAS but as a reagent immunologists in the 1970s used to inhibit or deplete experimental rodents of their macrophages, an immune cell type that acts as a clearing house for dead and dying cells (9, 10, 11).
While obviously doses used for such biological effects would be much higher than the amounts allowed in food, this is but an example to counter the inherently problematic notion that attributes of food additives deemed GRAS can or should be taken at face value.
Since modern food impacts everyone, rather than malign or nefarious motives, inadvertent use fueled by ignorance of their biological potential helps explain how processed foods chock full of myriad food additives have come to occupy such an extensive and expansive space within the Western food landscape since the mid-20th century.
While some have fixated on the toxic potential of many food additives, their real influence may be something far more insidious and sweeping, namely, large-scale modification of our microbiota, especially of those inhabiting our GI tract, which is how they may link Western diets with inappropriate or inappropriately persisting inflammation.
Many GRAS ingredients have long been presumed inert and our own cells deemed incapable of metabolizing them. However where microbiota are concerned, the relatively recent explosion in research steadily reveals otherwise. Study after study, ingredient after ingredient is now being shown subject to metabolism by specific microbes (12, 13, 14, 15, 16, 17, 18).
One of the most recent of such studies revealed how virulent strains of Clostridium difficile outcompete their more benign counterparts in utilizing Trehalose – Wikipedia, a sugar that until the 1990s was hard to manufacture at scale but is now prevalent in all manner of processed foods since it improves shelf-life and texture (19, 20). Industrial trehalose use coincides with C.diff outbreaks.
Experimental mouse models that imply correlation, not causation is the caveat about many diet-microbiota studies. Nevertheless, the emerging narrative plausibly argues Western diets appear to engender residence within our GI tracts of microbiota species whose harmful propensities outweigh benefits.
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7. Why the FDA doesn’t really know what’s in your food
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9. Catanzaro, Phillip J., Howard J. Schwartz, and Richard C. Graham Jr. “Spectrum and possible mechanism of carrageenan cytotoxicity.” The American journal of pathology 64.2 (1971): 387. https://www.ncbi.nlm.nih.gov/pmc…
10. Sawicki, John E., and Phillip J. Catanzaro. “Selective macrophage cytotoxicity of carrageenan in vivo.” International Archives of Allergy and Immunology 49.5 (1975): 709-714.
11. Rumjanek, V. M., S. R. Watson, and V. S. Sljivić. “A re-evaluation of the role of macrophages in carrageenan-induced immunosuppression.” Immunology 33.3 (1977): 423. https://www.ncbi.nlm.nih.gov/pmc…
12. Nickerson, Kourtney P., and Christine McDonald. “Crohn’s disease-associated adherent-invasive Escherichia coli adhesion is enhanced by exposure to the ubiquitous dietary polysaccharide maltodextrin.” PLoS One 7.12 (2012): e52132. http://journals.plos.org/plosone…
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14. Chassaing, Benoit, et al. “Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome.” Nature 519.7541 (2015): 92. https://pdfs.semanticscholar.org…
15. Cani, Patrice D. “Metabolism: Dietary emulsifiers—sweepers of the gut lining?.” Nature Reviews Endocrinology 11.6 (2015): 319.
16. Chassaing, Benoit, et al. “Dietary emulsifiers directly alter human microbiota composition and gene expression ex vivo potentiating intestinal inflammation.” Gut (2017): gutjnl-2016. http://gut.bmj.com/content/gutjn…
17. Statovci, Donjete, et al. “The impact of Western diet and nutrients on the microbiota and immune response at mucosal interfaces.” Frontiers in immunology 8 (2017): 838. The Impact of Western Diet and Nutrients on the Microbiota and Immune Response at Mucosal Interfaces
18. Roca-Saavedra, Paula, et al. “Food additives, contaminants and other minor components: effects on human gut microbiota—a review.” Journal of physiology and biochemistry (2017): 1-15.
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20. Collins, J., et al. “Dietary trehalose enhances virulence of epidemic Clostridium difficile.” Nature (2018).