Author: Zeena Haress

GLP-1 therapies have reshaped modern metabolic medicine. Drugs such as
semaglutide, liraglutide, and related incretin-based agents are used in the treatment of
clinically significant metabolic disease, most prominently type 2 diabetes, obesity, and
overweight states associated with cardiometabolic risk (rather than as simple cosmetic
weight-loss drugs, which would be highly dangerous to use in that way). Their
therapeutic effects include improving glycaemic regulation and, in obesity-directed
formulations, reducing appetite and body weight through central and gastrointestinal
GLP-1 signalling. Yet their biology is broader than glucose control or appetite regulation
alone. GLP-1 receptor signalling intersects with insulin dynamics, gastric emptying,
inflammatory tone, oxidative stress, mitochondrial health, as well as neuroimmune and
gut‒brain communication, which is becoming highly relevant to clinicians.

Photobiomodulation, or PBM, does not mimic GLP-1 receptor agonists, and it should
not be positioned as a replacement for them. However, emerging evidence suggests
that PBM may act on several of the same biological systems that GLP-1 therapies seek
to improve: cellular energy metabolism, redox balance, low-grade inflammation, glucose
handling, and potentially, gut-derived endocrine signalling. The clinically interesting
question is therefore not whether PBM “does what GLP-1 drugs do,” but whether PBM
could complement the physiological terrain in which GLP-1 therapies operate.

GLP-1 Therapies: The Biology

Native glucagon-like peptide-1 is an incretin hormone released primarily from intestinal
L-cells after food intake. Its best-established metabolic actions include:

• Enhancing glucose-dependent insulin secretion
• Suppressing glucagon release when glucose is elevated
• Slowing gastric emptying
• Increasing satiety and reducing food intake

These effects explain why GLP-1 receptor agonists have become central tools in type 2
diabetes and obesity management. Their efficacy is not simply behavioural; it is rooted
in a coordinated recalibration of endocrine and neural signals that govern nutrient
handling. At the cellular level, GLP-1 signalling has also been linked to reduced oxidative
stress, dampened inflammatory signalling, and preservation of mitochondrial function.
Reviews of GLP-1 biology describe activation of antioxidant pathways such as Nrf2,
reductions in reactive oxygen species, and modulation of inflammatory mediators. In
disease models, GLP-1 receptor agonists have shown neuroprotective and
immunomodulatory effects, although these findings remain more mature in preclinical
literature than in routine clinical neurology.

This matters because obesity, insulin resistance, type 2 diabetes, and many age-related
disorders are not driven by one isolated pathway. They involve overlapping
disturbances in mitochondrial efficiency, inflammatory burden, vascular function, an brain‒body signalling. GLP-1 therapies address part of that network. And now, the
question is whether PBM may support another part of it.

Photobiomodulation (PBM): The Biology

PBM uses red or near-infrared light delivered at non-thermal, low-intensity doses to
influence cellular function. Its most widely discussed mechanism involves the
mitochondrial respiratory chain, particularly cytochrome c oxidase, a terminal enzyme in
oxidative phosphorylation. One leading hypothesis is that red or near-infrared photons
help dissociate inhibitory nitric oxide from cytochrome c oxidase, thereby supporting
electron transport, mitochondrial membrane potential, and ATP production under
stressed conditions.

PBM is also associated with redox signalling, not simply “antioxidant effects.” Small,
controlled changes in reactive oxygen species can activate transcriptional programmes
involved in adaptation and repair, while excessive oxidative stress can damage proteins,
lipids, and DNA. This distinction is clinically important: PBM is dose-dependent, and the
field recognises a biphasic response, in which insufficient light may do little, an
appropriate dose may be beneficial, and excessive exposure may reduce benefit or
become counterproductive.

Across experimental systems, PBM has been associated with improved mitochondrial
function, reduced tissue inflammatory signalling, protection against oxidative injury, and
modulation of neuroinflammatory cascades. These actions do not make PBM a drug
analogue. Rather, they position it as a biophysical modulator of cellular resilience,
particularly in metabolically stressed tissue.

Where PBM and GLP-1 Biology Converge

1. Mitochondrial Function: A Shared Metabolic Pressure Point
Mitochondrial dysfunction is increasingly recognised as a feature of insulin resistance,
type 2 diabetes, obesity-related tissue stress, and many neurodegenerative conditions,
like Alzheimerʼs. GLP-1 receptor agonists have been reported to improve aspects of
mitochondrial respiration, redox state, and cellular energy handling in experimental and
translational literature.

PBM enters this discussion because mitochondria are also its leading proposed
biological target. By modulating cytochrome c oxidase activity, ATP production, and
redox signalling, PBM can support the energetic efficiency of tissues that are
metabolically strained. This overlap is not proof of therapeutic synergy, but it is
biologically meaningful: GLP-1 therapies may improve metabolic signalling from the
endocrine side, while PBM may support aspects of cellular energy handling from the
photobiological side.

For physicians, the nuance is important. PBM should not be framed as “boosting
metabolism” in a vague wellness sense. A more accurate statement is that PBM has
been shown, in a range of preclinical models, to influence mitochondrial respiration and oxidative stress responses; processes that are also implicated in the metabolic
disorders for which GLP-1 therapies are prescribed.

2. Oxidative Stress and Inflammation: Different Interventions, Overlapping Biology
Chronic metabolic disease is often accompanied by low-grade inflammatory activation
and oxidative burden. GLP-1 receptor activation has been linked to reductions in
reactive oxygen species, suppression of inflammatory pathways, and improved cellular
stress responses in multiple tissues.

Author: Zeena Haress

PBM has a parallel literature. Reviews and experimental studies report that PBM can
reduce pro-inflammatory signalling, alter immune-cell activation states, and attenuate
oxidative injury in diseased or damaged tissues. In a spinal cord injury model, for
example, PBM reduced activation of neurotoxic microglia and astrocytes and
suppressed Lcn2/JAK2‒STAT3-associated neuroinflammatory crosstalk. Although this is
not a metabolic disease model, it illustrates the broader capacity of PBM to modulate
inflammatory cell behaviour in stressed neural tissue.

This is where the concept of complementarity becomes scientifically defensible. GLP-1
therapies and PBM do not act through the same primary receptor. However, both may
favour a physiological shift away from oxidative and inflammatory overload and toward
a more regulated cellular environment. In a patient with obesity or type 2 diabetes, that
distinction may matter because metabolic improvement is not only a matter of lowering
glucose; it also involves reducing the biological consequences of chronic nutrient
excess and tissue stress.

3. Glucose Regulation: PBM Shows Early, But Not Yet Definitive, Metabolic Signals
The strongest clinical use case for GLP-1 therapies remains glycaemic and weight
management. PBM is not established as a treatment for diabetes, but its metabolic
literature is becoming harder to ignore.

A recent systematic review (da Rocha et al., 2026) of clinical PBM studies in type 2
diabetes found associations with reductions in fasting glucose, postprandial glucose,
and HbA1c, but rated the certainty of the evidence as very low to low, emphasising the
need for more standardised, high-quality trials.

Individual human studies also suggest a metabolic signal. One study reported that PBM
produced a dose- and time-dependent reduction in glycaemic in patients with type 2
diabetes. Another study (Scontri et al., 2023) found that a 15-minute exposure to 670
nm light reduced the post-glucose rise in blood glucose in healthy participants by
27.7% over two hours. These findings are intriguing, but they do not yet justify PBM as
a primary glucose-lowering therapy or as a validated enhancer of GLP-1 medications.
Essentially, PBM has preliminary human and preclinical evidence suggesting effects on
glucose handling and metabolic stress, but it remains an investigational adjunct rather
than a proven metabolic treatment.

4. The Gut‒Endocrine Axis: The Most Direct PBM‒GLP-1 Link So Far
The most compelling bridge between PBM and GLP-1 biology may not be in adipose
tissue or the brain first, but in the gut.

An animal study (Min et al., 2022) investigating duodenal dual-wavelength PBM in a type 2 diabetes model reported improved glucose intolerance, changes in serum insulin-
related parameters, and alterations in the gut microbiome. The study measured GLP-1, GIP, insulin, glucose tolerance, hepatic markers, and microbial composition, suggesting
that light delivered to the upper intestine may influence a wider entero-metabolic
network.

A Science Advances study (Sim et al., 2023) using an OLED catheter for internal
duodenal PBM in diabetic rats went further. The authors reported improvements in
metabolic features and described a dynamic rise in serum GLP-1 over one to four
weeks, alongside changes in food intake and insulin-related parameters. This is one of
the clearest indications that localized PBM applied to the gut may interact with
endogenous incretin biology, at least in preclinical models.
This does not mean that abdominal or duodenal PBM has been shown to reproduce the
efficacy of semaglutide or tirzepatide. It does, however, raise an important mechanistic
hypothesis: PBM may influence the gut environment and enteroendocrine signalling in ways that are relevant to GLP-1 physiology. For the evolution of gut-directed, non-
invasive interventions in metabolic disease, this is a field worth watching.

5. PBM, the Microbiome, and the Broader Metabolic Context
GLP-1 biology is tightly linked to nutrient sensing and intestinal physiology. Meanwhile,
the gut microbiome has emerged as a relevant player in obesity, glucose metabolism,
low-grade inflammation, and systemic metabolic tone. PBM studies have begun to
examine whether light delivered to the abdomen or gut can alter microbial composition
and inflammatory status. In mouse models, abdominal PBM has been reported to alter
gut microbial diversity, with the effect more evident after repeated near-infrared
exposure than after a single red-light treatment. Later reviews have proposed that PBM
may influence gut inflammation and microbiome balance, although the field remains
early and heterogeneous.

This matters for the GLP-1 discussion because it broadens the biological frame. GLP-1
therapies are often discussed at the level of weight and insulin. Yet their effects unfold
in a system where the gut, immune signalling, microbial metabolites, vagal pathways,
and central appetite circuits are deeply interconnected. PBMʼs emerging gut-directed
literature may eventually prove relevant to that wider context; not by imitating GLP-1
therapy, but by modulating peripheral systems that influence metabolic and
inflammatory signalling upstream.

6. The Brain-Metabolic Axis: A More Speculative, But Clinically Interesting Frontier
GLP-1 receptors are expressed in brain regions involved in appetite, reward, autonomic
regulation, and neuroendocrine control. GLP-1-based therapies are therefore
increasingly being explored beyond diabetes and obesity, including in
neurodegenerative and neuroinflammatory contexts. Reviews of GLP-1 receptor
agonists in Alzheimerʼs and Parkinsonʼs disease models highlight potential roles in
reducing neuroinflammation, supporting mitochondrial function, and limiting oxidative
injury, though definitive clinical applications remain under investigation.
PBM has its own growing neurobiological literature. Transcranial PBM has been studied
for its effects on mitochondrial activity, cerebral physiology, oxidative stress, and
neuroinflammatory pathways. In rodent sleep-deprivation models, transcranial
irradiation influenced hypothalamic oxidative and inflammatory parameters, and related
work examined BDNF and GLP-1 in the context of cognitive and age-dependent
responses. These studies are not evidence of a clinical PBM‒GLP-1 combination effect,
but they suggest a plausible point of intersection between light-based neuromodulation
and endocrine signals relevant to brain energy homeostasis. PBM and GLP-1 signalling both intersect with neuroenergetics, inflammation, and brain‒body metabolic communication. Their mechanistic overlap warrants study, but clinical synergy has not yet been established.

What PBM Cannot Yet Be Claimed to Do

A scientifically responsible article must be explicit about the limits of the evidence.
At present, there is no robust human clinical evidence showing that PBM enhances the
effectiveness of GLP-1 receptor agonists, reduces the required dose of GLP-1
medications, prevents GLP-1-related side effects, or replicates their pharmacological actions. The most direct GLP-1/PBM findings are preclinical and largely involve gut-directed PBM, endocrine measurements, or rodent neuro-metabolic models.

PBM also should not be described as a natural alternative to GLP-1 drugs. GLP-1
receptor agonists are receptor-targeted pharmacological agents with large clinical trial
programmes behind them. PBM is a non-pharmacological modality with promising but
still variable evidence across indications, where treatment parameters, anatomical
targets, dosing schedules, and endpoints are not yet standardised in metabolic
medicine.

A Balanced Interpretation

The most defensible way to discuss PBM alongside GLP-1 therapies is this:
GLP-1 receptor agonists act primarily through incretin receptor pharmacology to
improve glycaemic regulation, reduce appetite, and support weight loss. PBM acts
through photobiological modulation of cellular energy, redox signalling, and
inflammatory tone. The two are not equivalent, but their biology intersects in
metabolically relevant systems, creating a reasonable hypothesis for future research:
PBM may be most clinically interesting not as a competitor to GLP-1 therapies, but as a supportive adjunctive strategy that targets the cellular and systemic stress environment accompanying obesity, insulin resistance, and metabolic inflammation.

That hypothesis is especially relevant in three domains:

1. Metabolic resilience: mitochondrial function, oxidative stress, and glucose handling
2. Gut-directed biology: microbiome changes and possible modulation of endogenous
   incretin signalling
3. Brain‒body communication: hypothalamic, neuroinflammatory, and neuroenergetic
   pathways relevant to appetite and metabolic regulation
   

Each of these areas has early supporting literature, but each also requires far stronger
translational and clinical validation.
A Complement, Not a Substitute
GLP-1 therapies have transformed the treatment landscape for obesity and type 2
diabetes because they work with fundamental physiology: enteroendocrine signalling, insulin regulation, gastric motility, appetite circuits, and increasingly appreciated anti-inflammatory and cytoprotective pathways.

PBM may complement that biology by acting on a different but overlapping level, through mitochondrial efficiency, redox balance, inflammatory tone, and possibly gut-derived metabolic signalling. The most intriguing early evidence comes from gut-directed PBM studies showing changes in glucose regulation, microbiome composition,and GLP-1-associated endocrine patterns in diabetic animal models. Human metabolic
PBM studies are encouraging but not yet definitive.

For clinicians, the intellectually honest position is neither dismissal nor overclaiming.
PBM should not be marketed as a replacement for GLP-1 pharmacology. But the
biology is sufficiently convergent to justify a serious, research-led conversation about
whether light-based modulation of metabolic stress pathways could one day sit
alongside incretin-based therapies as part of a broader systems approach to metabolic
health.

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