Journal

Introduction — inflammation is not the problem; chronicity is

Inflammation is a fundamental protective mechanism. It is an adaptive biological response that enables repair, neutralisation of infectious agents, containment of aggression, and restoration of internal balance. Without acute inflammation, there would be no effective wound healing, no coherent immune defence, and no true capacity for survival [1].

Over recent years, however, research has described another, far more silent reality: when inflammation ceases to be transient and self-resolving and instead becomes chronic, diffuse and low-intensity, it no longer protects. It settles in as a biological “background noise”, disrupts metabolic signalling, reshapes the immune environment and progressively weakens the body’s resilience [1–3]. This is what is referred to as low-grade inflammation.

Low-grade inflammation does not present with clear flare-ups. It often precedes diagnosis—sometimes by years. It accompanies gradual drifts: persistent fatigue, unstable digestion, less restorative sleep, diffuse aches, abdominal weight gain, greater emotional fragility. The trap is simple: each of these signals may seem trivial on its own. It is their convergence—and above all their persistence—that should raise concern [1–3].

Physiologically, several sources may sustain it simultaneously: a less resilient gut microbiota and a compromised intestinal barrier (with increased translocation of pro-inflammatory signals), metabolic dysregulation (insulin resistance, excess visceral fat), chronic sleep debt, and a modern diet rich in ultra-processed food matrices—consistently associated in recent syntheses with systemic inflammatory biomarkers, particularly hs-CRP [7–9,24,25]. Low-grade inflammation is therefore not “a disease”; it is a biological terrain.

The aim of this article is not to diagnose, but to provide a rigorous interpretive framework: to identify 10 subtle signals which, when combined, outline a coherent picture of chronic low-grade inflammation—and, crucially, to understand why these signals exist, how they interact, and how to act on this terrain in a progressive, measurable and physiologically meaningful way [1–3].

I — The 10 subtle signals of chronic low-grade inflammation

Low-grade inflammation is not a dramatic clinical picture. It rarely manifests through obvious “medical” signs. Instead, it appears as a gradual drift in biological terrain, where several non-specific symptoms converge: fatigue, digestive instability, non-restorative sleep, diffuse pain, metabolic dysregulation, more reactive skin, greater emotional vulnerability [1–3]. What matters is not an isolated signal, but the overall coherence—especially when it persists over time.

1) Persistent fatigue: when the body runs “on low power”

Inflammatory fatigue is not simple tiredness from lack of rest. It is often described as a background loss of vitality, reduced drive, or a sense that the “battery never fully recharges”, even after a full night’s sleep. Biologically, this reflects the energetic cost of prolonged immune activation: maintaining inflammatory pathways requires resources, diverts energy away from repair and adaptation, and alters how cells utilise substrates [1,4].

A key point is the convergence between chronic inflammation and energy metabolism. Several recent syntheses describe the inflammation–metabolism axis as a central driver of functional fatigue: cytokines (notably IL-6 and TNF-α) can impair mitochondrial efficiency, promote oxidative stress, and reduce bioenergetic efficiency [4,5]. This helps explain why such fatigue is often associated with slower recovery and reduced exercise tolerance, even in the absence of any identifiable acute inflammatory disease.

2) Fluctuating digestive symptoms: the gut as a source of systemic inflammation

Bloating, post-prandial discomfort, irregular bowel habits, digestive hypersensitivity—these symptoms are often labelled “functional”. Yet the gut is one of the primary interfaces between the environment (diet, microbiota) and the immune system. Dysbiosis and a weakened intestinal barrier can increase exposure to pro-inflammatory microbial signals, with systemic consequences, even if modest [6].

The concept of metabolic endotoxaemia illustrates this mechanism well: a chronic, low-level but persistent rise in bacterial components (notably LPS) is associated with low-grade inflammation and metabolic disturbances such as insulin resistance and visceral fat accumulation [7,8]. Recent reviews emphasise the central role of this “microbiota–barrier–endotoxaemia–inflammation” continuum in modern metabolic trajectories [7–9]. In other words, when digestive and metabolic dysregulation coexist, the inflammatory hypothesis becomes particularly compelling.

3) Diffuse pain and stiffness: when inflammation amplifies pain

Low-grade inflammation does not always produce classic inflammatory pain (redness, heat, swelling). More often, it manifests as diffuse aches, morning stiffness, heightened sensitivity, or slow muscle recovery. The link between systemic inflammation and chronic pain is increasingly explored: persistent elevation of inflammatory mediators can influence nociceptive sensitivity and neuro-immune balance, amplifying pain perception [10,11].

Recent studies in musculoskeletal pain—including chronic low back pain—document altered circulating cytokine profiles in certain patients, suggesting that in some cases pain is not purely mechanical, but embedded in a broader biological context [10,12]. Clinically, the implication is simple: when diffuse pain, fatigue and poor sleep coexist, one should think “terrain” rather than isolated symptoms.

4) Brain fog: cognition as a silent inflammatory target

“Brain fog” is often underestimated because it is subjective, gradual and easily attributed to stress. Yet links between peripheral inflammation (CRP, IL-6 and other markers) and cognition are increasingly documented in reviews and longitudinal studies [13]. These findings do not suggest that inflammation explains everything, but that it can contribute to reduced cognitive performance via neuro-immune pathways and changes in the neurochemical environment [13–15].

This signal gains weight when it fits into a broader picture: sleep disturbance, digestive dysregulation, persistent fatigue and a sense of diminished mental clarity. The issue is not to diagnose neurological disease, but to recognise that cognition is sensitive to low-grade inflammatory signalling—and may improve when the underlying terrain is addressed [13,15].

5) Emotional fragility: anxiety, irritability, reduced motivation

Contemporary research increasingly clarifies the interactions between inflammation, the stress (HPA) axis, neurotransmission and emotional symptoms. Multiple recent reviews and analyses—including genetic and causal-inference approaches—show robust associations between inflammatory markers and depressive/anxious symptoms, with active scientific debate on mechanisms and causality direction [16–18].

Clinically, the useful perspective is not “inflammation causes depression”, but rather: an inflammatory terrain can destabilise emotional balance, especially when combined with sleep debt, dysbiosis, glycaemic instability and chronic stress. This integrated view avoids reductionism—neither purely psychological (“it’s all in the head”) nor purely biological (“it’s only inflammation”)—and instead adopts a systems-based interpretation [16–18].

6) Abdominal weight gain or “stuck” weight: modern meta-inflammation

Low-grade inflammation is tightly interwoven with metabolism. The literature has long described meta-inflammation: an inflammatory state sustained by energy overload, visceral adiposity, insulin dysregulation and lipid signalling [19]. This framework has been enriched by work on endotoxaemia, the gut–liver axis and the effects of modern food environments [7–9,19].

Clinically, this often translates into a familiar profile: gradual weight gain (particularly abdominal), resistance to weight loss, post-meal fatigue, cravings and energy fluctuations. This is not a question of willpower—it is often dysregulated physiology. That is precisely why effective strategies focus on modifying the terrain (diet quality, glycaemic stability, sleep, activity), rather than isolated restriction.

7) Non-restorative sleep: a vicious inflammation–sleep cycle

Sleep is a major immune modulator. Experimental data and recent meta-analyses show that even partial sleep restriction over several nights can increase peripheral inflammatory markers, notably IL-6 and CRP, even in young individuals [20]. Other recent studies confirm the impact of sleep duration and quality on inflammatory parameters [21].

Conversely, low-grade inflammation can disrupt biological rhythms, reduce sleep depth and impair recovery. This is one of the most common vicious cycles in practice: poorer sleep → more inflammation → poorer sleep. When this signal appears alongside fatigue, emotional fragility and abdominal weight gain, the inflammatory logic becomes highly coherent [20,21].

8) “Reactive” skin: when the gut–immune axis shows on the surface

The skin is an immune organ. Redness, persistent blemishes, inflammatory dryness, subtle eczema, rosacea—these are non-specific signs, but recent research increasingly develops the concept of the gut–skin axis: a bidirectional dialogue between microbiota, intestinal barrier, systemic immunity and cutaneous inflammation [22,23].

Recent reviews describe how dysbiosis and increased intestinal permeability can facilitate translocation of inflammatory signals into circulation, influencing cutaneous immune balance [22,23]. This signal becomes particularly suggestive when associated with digestive symptoms and a pro-inflammatory dietary pattern (often rich in ultra-processed foods).

9) Recurrent infections or slow recovery: inflammation is not effective immunity

A counter-intuitive point: one can be “inflamed” yet immunologically less resilient. An immune system chronically activated at low intensity can lose adaptive efficiency, prolonging recovery. This profile is frequently discussed in the literature on immunity and chronic inflammation: it is not “strong” immunity, but desynchronised immunity [1,3].

Clinically, this appears as recurrent colds, prolonged convalescence, lingering fatigue after infection, or seasonal vulnerability. Again, the value lies in contextualising the symptom within the terrain: sleep, stress, nutrition, digestion and physical activity.

10) “Slightly elevated” but persistent lab values: patterns matter more than single numbers

Low-grade inflammation is rarely identified through a single “out-of-range” marker. It is detected through persistent trends: hs-CRP above optimal range, elevated IL-6 or TNF-α in certain contexts, associated metabolic abnormalities (triglycerides, glucose, waist circumference), and sometimes indirect markers of barrier disruption (LBP, zonulin, depending on assessment strategy) [7–9].

This point is crucial: the aim is not to over-medicalise biological variation, but to identify coherence between symptoms and biology in order to design a progressive, measurable and realistic corrective strategy. That is what distinguishes a “symptom-by-symptom” reading from a true “terrain” approach.

A transversal factor not to overlook: ultra-processed foods

Although not a “signal” per se, ultra-processed food consumption is now one of the strongest contextual factors for understanding modern inflammatory terrain. Recent syntheses consistently report associations between high UPF intake and elevated systemic inflammatory biomarkers, with a particularly robust signal for CRP/hs-CRP [24]. Some recent studies explicitly identify hs-CRP as a sensitive marker linked to high UPF dietary patterns [25]. This helps explain why credible anti-inflammatory strategies often begin by improving food-matrix quality before adding anything else.

II — Low-grade inflammation: scientific definition and biological framework

Low-grade inflammation refers to a state of chronic, diffuse, low-intensity inflammatory activation, without an identifiable acute infectious trigger. It differs from classical inflammatory diseases by its persistent, systemic and often asymptomatic nature—yet it remains biologically active [1–3].

Scientifically, it is generally characterised by:

• a moderate but sustained elevation of pro-inflammatory cytokines (notably IL-6, TNF-α, sometimes IL-1β),
• chronic activation of innate inflammatory signalling pathways (NF-κB, JAK/STAT),
• constant interaction with energy metabolism, adipose tissue, the gut microbiota and biological rhythms [1–3].

Unlike acute inflammation, this state does not resolve spontaneously. It maintains a background level of cellular stress, alters metabolic signalling, diverts adaptive resources and gradually erodes organismal resilience [1,2].

It is essential to understand that low-grade inflammation is not a disease in itself. It is a biological terrain upon which metabolic, cardiovascular, neuro-cognitive or musculoskeletal disorders may later emerge [1–3].

III — Biomarkers: what is relevant to observe (and how to interpret them)

These biomarkers are never interpreted as isolated diagnostic tools, but as indicators of terrain whose relevance depends on their evolution over time and coherence with the overall clinical context.

There is no single marker of low-grade inflammation. Detection relies on a profile-based reading, combining biology, symptoms and lifestyle context.

The cornerstone marker: high-sensitivity CRP (hs-CRP)

High-sensitivity CRP is one of the most widely used biomarkers for exploring low-intensity systemic inflammation. At moderately elevated but persistent levels, it is associated with increased cardio-metabolic risk and reflects a chronic inflammatory terrain [1,24].

Its main value lies not in one-off diagnosis, but in longitudinal monitoring in relation to changes in lifestyle, diet and metabolism.

Associated metabolic markers

Low-grade inflammation very often sits within a specific metabolic context:

• high-normal or unstable fasting glucose,
• elevated triglycerides and reduced HDL,
• gradual increase in waist circumference,
• liver-enzyme alterations suggesting metabolic steatosis.

These abnormalities are not secondary—they actively contribute to the modern meta-inflammatory state described in the literature [19].

Gut–barrier–endotoxaemia axis: a terrain hypothesis

In certain clinical contexts, assessment of indirect intestinal-barrier markers (LBP, zonulin) may provide additional insight, linked to the concept of metabolic endotoxaemia [7–9].

It is essential to emphasise that these markers are never interpreted in isolation, but integrated into a global reading of digestive, metabolic and inflammatory terrain.

IV — The main biological sources of low-grade inflammation

Low-grade inflammation never arises from a single factor. It results from the convergence of multiple, often interwoven sources of biological stress.

1) Nutritional meta-inflammation

Chronic energy overload, repeated glycaemic spikes and accumulation of visceral fat activate innate immune pathways via adipose tissue and the liver. This meta-inflammation is now considered a central driver of modern chronic inflammation [19].

2) Intestinal dysbiosis and increased permeability

Reduced microbial diversity and a weakened intestinal barrier promote translocation of pro-inflammatory signals into circulation, sustaining low-grade immune activation [7–9].

3) Chronic sleep debt

Even moderate but repeated sleep deprivation is associated with increased peripheral inflammatory markers. Sleep is a central immune regulator; when it is compromised, inflammation tends to persist [20,21].

4) Sedentary behaviour and loss of functional muscle mass

Muscle mass exerts anti-inflammatory effects via protective myokines. Its reduction, combined with physical inactivity, contributes to an unfavourable inflammatory and metabolic terrain.

5) Ultra-processed diets

Recent syntheses show a robust association between high consumption of ultra-processed foods and elevated systemic inflammatory biomarkers, particularly hs-CRP [24,25]. This reflects not a single food, but a repeated pro-inflammatory dietary matrix over time.

Understanding the biological sources of low-grade inflammation allows intervention at the right level—not by attempting to “block” inflammation, but by durably modifying the biological environment that sustains it.

V — Anti-inflammatory nutrition: acting on terrain, not symptoms

A relevant nutritional approach does not aim to “switch off” inflammation, but to reduce the biological conditions that make it chronic.

Several levers are now well documented:

• progressive reduction of ultra-processed foods in favour of intact food matrices [24,25],
• adequate fibre and polyphenol intake to support a more resilient microbiota and barrier integrity [6–9],
• lipid quality (omega-3/omega-6 balance, virgin oils),
• glycaemic stability through structured meals adapted to individual context,
• coherent biological rhythms: sleep, meal timing, recovery.

The effectiveness of these levers depends on their consistency over time, not on isolated actions.

Three simple priorities over 30 days

• Reduce the frequency of ultra-processed foods, without a prohibition mindset.
• Systematically reintroduce fibre and diverse plant foods at every meal.
• Protect sleep as a major inflammatory lever.

Conclusion — recognising the terrain to act upstream

Low-grade inflammation is neither inevitable nor a fixed diagnosis. It is a modifiable biological state that develops gradually and can, to a large extent, be corrected when its sources are identified.

Recognising subtle signals, understanding their coherence, and acting on fundamental levers—nutrition, metabolism, microbiota, sleep—helps restore biological resilience and prevent progression towards established chronic disease [1–3].

When to consult

Medical evaluation is necessary in cases of:

• unexplained severe fatigue or unintentional weight loss,
• acute inflammatory pain or persistent fever,
• clearly elevated or evolving laboratory abnormalities,
• severe digestive symptoms or those associated with deficiencies.

FAQ — Low-grade inflammation

What are the most common symptoms?
Chronic fatigue, unstable digestion, diffuse pain, non-restorative sleep, abdominal weight gain, emotional fragility.

Is CRP alone sufficient?
No. CRP is a useful indicator, but interpretation must always be global and contextual.

Are anti-inflammatory drugs a solution?
They may relieve symptoms, but they do not correct the underlying biological terrain driving chronic inflammation.

Can inflammation be reduced without a strict diet?
Yes. Evidence shows that gradual improvements in diet quality and lifestyle are often more effective and sustainable.

Bibliography

[1] Furman D. et al. (2019). Chronic inflammation in the etiology of disease across the life span. Nature Medicine.
https://www.nature.com/articles/s41591-019-0675-0

[2] Li X. et al. (2023). Inflammation and aging. Signal Transduction and Targeted Therapy (Nature portfolio).
https://www.nature.com/articles/s41392-023-01502-8

[3] Liu Z. et al. (2023). Immunosenescence. Signal Transduction and Targeted Therapy (Nature portfolio).
https://www.nature.com/articles/s41392-023-01451-2

[4] Fan J. et al. (2025). ME/CFS review – cytokines, energy, inflammation. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12801797/

[5] Jiang Y. et al. (2026). The inflammation–energy metabolism axis. Immunological Investigations.
https://link.springer.com/article/10.1007/s00223-025-01473-8

[6] Peña-Durán E. et al. (2025). Microbiota and inflammatory markers. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC11854938/

[7] Jian E. et al. (2025). Metabolic endotoxemia and gut microbiota. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12446963/

[8] Chen B. et al. (2025). Gut-derived lipopolysaccharides and metabolic endotoxemia. AJP Endocrinology and Metabolism.
https://journals.physiology.org/doi/10.1152/ajpendo.00355.2025

[9] Dimeji IY. et al. (2025). Gut microbiota, gut barrier malfunction and inflammation in MetS. ScienceDirect.
https://www.sciencedirect.com/science/article/pii/S3050567425000094

[10] Enrico VT. et al. (2025). Systemic inflammation and chronic low back pain. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12439354/

[11] Schipholt IJL. et al. (2026). Neuroimmune interactions in musculoskeletal conditions. ScienceDirect.
https://www.sciencedirect.com/science/article/pii/S2468781225002176

[12] Anyfanti P. et al. (2025). Targeting inflammatory pathways in chronic low back pain. Pharmaceuticals.
https://www.mdpi.com/1424-8247/18/11/1612

[13] Leonardo S. et al. (2023). Association of inflammation and cognition in the elderly. Frontiers in Aging Neuroscience.
https://www.frontiersin.org/articles/10.3389/fnagi.2023.1069439/full

[14] Griseta C. et al. (2023). Serum IL-6 and cognitive impairment. Heliyon.
https://www.cell.com/heliyon/fulltext/S2405-8440(23)01179-9

[15] Slevin M. et al. (2025). CRP/IL-6, stress, pain sensitivity and cognitive decline. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12692357/

[16] Ye X. et al. (2025). Re-examination of inflammation in major depressive disorder. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12650186/

[17] Mac Giollabhui N. et al. (2025). Inflammation and neuropsychiatric symptoms. Translational Psychiatry.
https://www.nature.com/articles/s41398-025-03372-w

[18] Nava RG. et al. (2025). Neuroimmune cytokine networks in MDD. Translational Psychiatry.
https://www.nature.com/articles/s41398-025-03532-y

[19] Jian E. et al. (2025). Metabolic endotoxemia and metabolic disturbances. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12446963/

[20] Effects of Experimental Sleep Deprivation on Peripheral Inflammation. Journal of Sleep Research (2025).
https://onlinelibrary.wiley.com/doi/10.1111/jsr.70099

[21] Sochal M. et al. (2024). Effect of sleep and its restriction on inflammatory factors. Scientific Reports.
https://www.nature.com/articles/s41598-024-68498-1

[22] Zhao Y. et al. (2025). The gut–skin axis. PMC.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12494302/

[23] Lopez MFS. et al. (2025). Skin and gut microbiota dysbiosis. ScienceDirect.
https://www.sciencedirect.com/science/article/pii/S2950194625001104

[24] Ciaffi J. et al. (2025). Ultra-processed food consumption and systemic inflammatory biomarkers. Nutrients.
https://www.mdpi.com/2072-6643/17/18/3012

[25] Sajan K. et al. (2025). Ultra-processed foods and increased hs-CRP. PubMed.
https://pubmed.ncbi.nlm.nih.gov/40912444/