1 – Paradigmatic cases (In depth of Chronic low-grade inflammation (or chronic silent inflammation)
Obesity
Obesity—especially visceral obesity—is accompanied by a state of chronic low-grade inflammation. Excess adipose tissue secretes pro-inflammatory cytokines (such as TNF-α and IL-6) that contribute to the development of insulin resistance. It is therefore not surprising that obese patients often show elevated levels of C-reactive protein (CRP) (a marker of systemic inflammation) and a higher risk of type 2 diabetes. Lifestyle interventions aimed at weight reduction (a balanced diet and exercise) help to “cool down” this metabolic inflammation, also improving clinical parameters.
Metabolic syndrome
Metabolic syndrome is closely associated with a state of chronic low-grade (or “silent”) inflammation, in which excess visceral fat acts as an endocrine organ by secreting pro-inflammatory cytokines (such as IL-6 and TNF-α). This persistent process—often referred to as “meta-inflammation”—promotes insulin resistance, vascular dysfunction, and increases the risk of diabetes and cardiovascular disease.
Rheumatoid arthritis (autoimmune disease)
References
Wellen & Hotamisligil, J Clin Invest, 2003
Shoelson et al., J Clin Invest, 2006
Rheumatoid arthritis
Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease that primarily affects the joints, causing pain, swelling, and symmetrical stiffness, with onset often between 40 and 60 years of age. The immune system mistakenly attacks healthy tissues, creating chronic low-grade inflammation which, if left untreated, leads to progressive deformities and joint damage.
Biomarkers
The most commonly used markers of low-grade inflammation include C-reactive protein (CRP), interleukin-6 (IL-6), fibrinogen, and reactive oxygen species (ROS). These markers can be measured through blood tests and indicate a chronic inflammatory state that may be associated with various health conditions.
References
McInnes & Schett, NEJM, 2011
Smolen et al., Lancet, 2016
2 – Appendix A
Generalized inflammation, also known as systemic inflammation, is a condition in which the inflammatory process simultaneously involves multiple body districts rather than remaining confined to a specific site. This means that inflammatory mechanisms—normally activated as a protective response to infections, injuries, or tissue damage—remain diffusely and persistently active.
Systemic inflammation can develop in two main ways, characterized by different mechanisms, onset times, and clinical significance. On the one hand, it may result from the generalization of an initially localized acute inflammation; on the other, it may arise from the progressive extension of a low-grade chronic inflammatory state, which over time becomes systemic.
In the first case, inflammation begins at a specific site—such as pneumonia, appendicitis, or an infected wound—and rapidly spreads throughout the body. This occurs due to the massive release of inflammatory mediators, including cytokines (such as TNF-α, IL-1, IL-6), prostaglandins, and other pro-inflammatory molecules that enter the circulation, producing a generalized response. Typical examples include sepsis, septic shock, extensive burns, and major trauma. This form—known as acute systemic inflammation or SIRS (Systemic Inflammatory Response Syndrome)—is characterized by rapid onset, high intensity, and marked symptoms such as high fever, tachycardia, hypotension, and major metabolic alterations.
In the second case, inflammation is slow, persistent, and low-intensity. It initially affects one or more specific tissues—such as adipose tissue, the gut, or the joints—and later tends to spread systemically. The underlying mechanism is the continuous production of small amounts of inflammatory mediators that do not trigger an evident acute response but progressively accumulate over time. This condition is termed chronic low-grade systemic inflammation and is frequently associated with obesity, type 2 diabetes, metabolic syndrome, cardiovascular disease, and autoimmune disorders.
Among the main sites of origin of low-grade chronic inflammation, the gut plays a central role due to its large surface area, intense immune activity, and close interaction with the microbiota. Alterations in the intestinal barrier and microbial composition can promote the translocation of pro-inflammatory molecules into the bloodstream, contributing to the systemic spread of the process.
The causes of systemic inflammation—especially in its chronic form—are multiple and include chronic or recurrent infections, obesity, chronic inflammatory diseases such as rheumatoid arthritis and ulcerative colitis, chronic stress, an unbalanced diet rich in saturated fats, sugars, and ultra-processed foods, deficiencies of vitamins, minerals, and antioxidants, as well as smoking and excessive alcohol consumption.
Symptoms of generalized inflammation may vary depending on the cause and severity, but frequently include chronic fatigue, widespread muscle and joint pain, difficulties with concentration and memory, mood swings with irritability, anxiety or depression, digestive disturbances such as constipation or diarrhea, and in some cases a mild, persistent fever.
Over the long term, systemic inflammation represents an important risk factor for numerous chronic diseases, including cardiovascular disease (hypertension, atherosclerosis, myocardial infarction), type 2 diabetes, certain cancers (especially colon and breast), kidney disease, and worsening of autoimmune conditions.
In summary, systemic inflammation can reflect either an acute response that becomes generalized or the outcome of a low-grade chronic process that progressively extends. Although these are different conditions, both involve the simultaneous involvement of multiple organs and systems and have a relevant impact on overall health.
3 – Appendix B
Undigested food
Undigested food can trigger chronic low-grade inflammation, a biological process known as metabolic endotoxemia.
Here are the main mechanisms linking impaired digestion to inflammation:
1. “Leaky gut” (intestinal permeability)
When food macromolecules are not properly broken down (due to enzyme deficiency or insufficient chewing), they can damage the intestinal tight junctions.
Mechanism: Fragments of undigested proteins and bacterial toxins (LPS) pass directly into the bloodstream.
Response: The immune system recognizes these particles as “intruders,” activating a persistent but mild systemic inflammatory response.
2. Dysbiosis and fermentation
Undigested food reaching the colon becomes a substrate for fermentation by pathogenic bacteria.
Protein putrefaction: If proteins are not digested in the stomach/small intestine, their breakdown in the colon produces toxic metabolites such as ammonia and hydrogen sulfide, which irritate the intestinal mucosa and increase pro-inflammatory cytokine levels.
Excess LPS: Overgrowth of Gram-negative bacteria increases lipopolysaccharides (LPS), among the most powerful activators of low-grade inflammation detectable via hs-CRP.
3. Non–IgE-mediated food intolerances
Unlike acute allergies, constant exposure to foods the body cannot properly process (e.g., lactose or fructose malabsorption) keeps the immune system in a state of chronic alert.
Signs to monitor
If you suspect your inflammation is linked to digestion, look for:
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Immediate or post-prandial abdominal bloating
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Visible food fragments in the stool
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Brain fog after meals
4 – A special case: the role of gluten
“The role of gluten: Gluten exerts multiple harmful effects that compromise human health, not only in gluten-dependent diseases but also in chronic inflammatory conditions unrelated to gluten. After consumption, indigestible gluten peptides are modified by luminal microbial transglutaminase or transported across the intestinal epithelium to interact with the densely populated immune cells of the mucosa. As disruptors of intestinal permeability, undigested gluten peptides compromise the integrity of tight junctions, allowing foreign immunogenic molecules to reach internal compartments. Gliadin peptides are systemically distributed to remote organs, where they encounter endogenous tissue transglutaminase. Following post-translational deamidation or transamidation, the peptides become immunogenic and pro-inflammatory, inducing organ dysfunction and pathology. Cross-reactivity and sequence homology between gluten/gliadin peptides and human epitopes may contribute to molecular mimicry in the induction of autoimmunity. As proof of concept, gluten withdrawal alleviates disease activity in chronic inflammatory, metabolic, and autoimmune conditions, and even in neurodegeneration. We recommend combining a gluten-free diet with the Mediterranean diet to leverage the advantages of both. Before recommending gluten withdrawal for non–gluten-dependent conditions, patients should be asked about intestinal symptoms and screened for celiac-associated antibodies. The current list of gluten-induced diseases includes celiac disease, dermatitis herpetiformis, gluten ataxia, wheat allergy, and non-celiac gluten sensitivity. Given that gluten is a universal pro-inflammatory molecule, other non-celiac autoinflammatory and neurodegenerative conditions should be investigated for potential gluten elimination.” Gluten is a Proinflammatory Inducer of Autoimmunity. Aaron Lerner et al. Journal of Translational Gastroenterology 2024; 2(2):109–124. DOI: 10.14218/JTG.2023.00060.
Bibliographic references
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Furman D, et al. Chronic inflammation in the etiology of disease across the life span. Nature Medicine. 2019.
A landmark review describing systemic chronic inflammation as a central trait in the major causes of global morbidity (cancer, cardiovascular disease, diabetes, chronic kidney disease, and others) and discussing social, environmental, and biological drivers. -
Franceschi C, et al. Inflamm-aging and immune-metabolic changes with aging. Cell. 2018.
This article introduces the concept of inflammaging—age-associated low-grade chronic inflammation—and highlights the role of persistent inflammatory mediators. -
Khanna D, Khanna S, et al. Obesity: A chronic low-grade inflammation and its markers. Journal of Inflammation Research. 2020.
A review analyzing obesity as a paradigmatic model of low-grade systemic inflammation, with extensive discussion of key inflammatory markers produced by adipose tissue. -
Chen L, et al. Inflammatory responses and inflammation-associated diseases in organs. Journal of Biomedical Research. 2017.
A comprehensive review of the molecular mechanisms of acute and chronic inflammatory responses and their implications in multiple systemic diseases (cardiovascular, metabolic, autoimmune, and neoplastic).
