The Light You Eat Under Affects Your Blood Sugar. Here's What the Research Actually Says.
Written by Jessica Diakoumakos, Naturopath (BHSc Naturopathy) · Emba Wellness, Melbourne
Natural sunlight contains red light wavelengths that stimulate mitochondria to use glucose more efficiently — reducing blood sugar elevation after eating and improving overall metabolic stability throughout the day. A 2024 study published in the Journal of Biophotonics found that just 15 minutes of red light exposure reduced blood sugar elevation after eating by 27.7%. A 2025 controlled study published in Cell Metabolism found that people exposed to natural daylight spent significantly more time in normal blood sugar range compared to those under artificial light. Because poor blood sugar regulation drives fatigue, hormonal disruption, gut dysfunction, mood instability, and difficulty managing weight, understanding the relationship between light and metabolism has significant clinical implications. This post explains the mechanism, the research, and why Melbourne naturopath Jessica Diakoumakos recommends daily outdoor light exposure as a first-line metabolic health strategy.
I've been eating outside as much as I possibly can lately.
Not just because I love fresh air — although I do — but because I read two papers on sunlight and blood sugar regulation that I haven't been able to stop thinking about since.
And as a naturopath who works with women whose symptoms are often rooted in metabolic dysfunction they don't even know they have, this feels like genuinely important, underutilised information.
So let's get into it.
Why Sunlight Affects Your Blood Sugar — The Mechanism
Most people know sunlight is good for vitamin D. But what's far less talked about is what natural light does at a mitochondrial level.
Your mitochondria are the energy-producing structures inside your cells. Their primary job is to take glucose from your blood and convert it into ATP — the molecule your body actually runs on. How efficiently they do this job has a direct impact on how much glucose stays in your bloodstream after eating.
Here's where it gets interesting: natural sunlight contains red light wavelengths — around 670 nanometres — that directly stimulate mitochondrial activity. When those red light wavelengths hit your skin and eyes, your mitochondria essentially shift into a higher gear, consuming more glucose and producing more energy more efficiently.
A 2024 study published in the Journal of Biophotonics tested this directly. Just 15 minutes of 670nm red light exposure reduced blood sugar elevation after eating by 27.7% over two hours, with maximum blood sugar spiking reduced by 7.5% (Powner et al., 2024).
The mechanism, as the researchers explain it: red light increases mitochondrial membrane potential and ATP production, which increases cellular demand for glucose — meaning your cells pull more glucose out of your bloodstream, and less of it ends up circulating as a spike.
The Problem With Artificial Light
Here's where modern life becomes a problem.
LED lighting — which now dominates almost every indoor environment — is heavily weighted toward blue wavelengths (around 450nm). It has almost no red light content at all. And it turns out this matters enormously for your metabolism.
Blue light on its own has been shown to reduce mitochondrial function and impair ATP production (Powner et al., 2024). The researchers describe our indoor environments as "red-starved" — and suggest that long-term exposure to blue-dominant artificial lighting, without the balancing red wavelengths of natural sunlight, may be a significant and largely overlooked contributor to blood sugar dysregulation and metabolic disease.
This is particularly relevant given that we now spend almost 90% of our time indoors, largely under artificial lighting that lacks the wavelength spectrum our mitochondria were designed to work with.
What the 2025 Cell Metabolism Study Found
The second paper takes this even further — and its findings are genuinely remarkable.
Researchers from the University of Geneva, Maastricht University, and the German Diabetes Center conducted a controlled crossover study in people with type 2 diabetes. Participants spent time in two different light conditions — one with wide-window natural daylight, one with artificial lighting only — and their blood sugar was tracked continuously throughout (Harmsen et al., 2025).
The results were striking. When exposed to natural light, participants exhibited more stable blood sugar levels and an overall improvement in their metabolic profile. Blood sugar levels were in the normal range for 59% of the time under natural daylight compared to just 51% under artificial light.
The researchers also found that natural light improved fat oxidation — meaning the body was better able to switch between burning carbohydrates and burning fat for fuel, which is a key marker of metabolic flexibility and overall metabolic health.
The researchers noted that we spend almost 90% of our time indoors, under lower light intensity and a narrower wavelength spectrum than natural daylight provides, and raised the question of whether lack of natural light could be contributing to the rising incidence of metabolic disease.
Why This Matters Beyond Diabetes
You might be reading this thinking — I don't have diabetes, so does this apply to me?
Absolutely — and here's why.
Blood sugar dysregulation exists on a spectrum. You can have chronically unstable blood sugar, poor insulin sensitivity, and significant metabolic dysfunction for years — even decades — before it shows up as a formal diagnosis on a standard blood test. In the meantime, it's quietly driving symptoms that most women are told are just "normal" or "stress."
As a Melbourne naturopath working with women across gut health, hormonal health, and energy — poor blood sugar regulation is one of the most common underlying drivers I see. Here's what it looks like in practice:
Energy
Unstable blood sugar creates the classic spike-and-crash cycle. After a meal high in refined carbohydrates or sugar, blood sugar rises sharply, insulin spikes to bring it back down, and then it overshoots — leaving you in a low-blood-sugar state that your body interprets as an emergency. The result is that familiar 2pm energy crash, brain fog, and desperate craving for something sweet or caffeinated. Stable blood sugar means your cells have a consistent, steady fuel supply — and you feel the difference.
Hormones
This is one of the most important and most underappreciated connections in women's health. Insulin is itself a hormone — and when it's chronically elevated, it disrupts the entire hormonal system.
High insulin suppresses SHBG (sex hormone binding globulin), which means more free testosterone circulates in the blood. This is a key driver of the androgen excess symptoms in PCOS — the acne, the scalp hair thinning, the unwanted facial hair, the irregular cycles. Insulin resistance affects up to 70% of women with PCOS (Diamanti-Kandarakis & Dunaif, 2012) and is now increasingly recognised as central to the condition, not just a side effect of it.
Chronically elevated insulin also dysregulates cortisol, disrupts the communication between your brain and your ovaries, and impairs progesterone production. If your periods are irregular, your PMS is severe, or your hormonal symptoms feel out of proportion to what your tests show — blood sugar regulation is worth looking at.
Gut Health
Blood sugar spikes drive systemic inflammation — and the gut lining is one of the first places that inflammation takes hold. Chronic blood sugar dysregulation increases intestinal permeability (leaky gut), disrupts the composition of the gut microbiome, and feeds opportunistic bacteria and yeast that thrive on excess glucose.
It also impairs the migrating motor complex — your gut's self-cleaning mechanism that runs between meals — which contributes to bloating, SIBO risk, and digestive sluggishness. If you're dealing with IBS or unexplained bloating, blood sugar regulation is part of the root cause picture.
Mood and Mental Health
Your brain runs almost exclusively on glucose and is exquisitely sensitive to fluctuations. When blood sugar drops sharply after a spike, your body triggers a cortisol and adrenaline response — which is why you feel anxious, irritable, or emotionally flat when you're hungry or crashing after a meal.
Chronically unstable blood sugar is also associated with lower serotonin production, higher inflammatory cytokines that cross the blood-brain barrier, and impaired neurotransmitter synthesis. Stable blood sugar is one of the most underrated mental health interventions available — and it's free.
Immune Function
High blood sugar directly impairs immune cell function — particularly neutrophils and natural killer cells, your first line of defence. It also maintains the body in a state of chronic low-grade inflammation, which keeps your immune system perpetually activated and eventually depletes it. A chronically activated immune system is less capable of responding to actual threats — and more vulnerable to dysregulation over time.
Weight
Chronically elevated insulin is one of the most potent fat-storage signals in the body. Insulin tells your cells to store energy as fat — particularly around the abdomen — and simultaneously blocks fat burning. If weight loss feels impossible despite doing everything right, blood sugar and insulin regulation is often the missing piece. This is exactly the kind of pattern that functional pathology testing is designed to identify — fasting insulin and HOMA-IR tell a very different story to fasting glucose alone.
“I eat outside every chance I get — and it has nothing to do with fresh air. When you understand what natural light actually does to your mitochondria and your blood sugar, eating your lunch at your desk under fluorescent lighting starts to feel like a very strange choice.”
The Circadian Rhythm Connection
There's a third layer to this that's worth understanding — and it connects directly to the grounding research I've written about elsewhere on this blog.
Your body runs on a circadian rhythm — a 24-hour biological clock that governs virtually everything from hormone production to digestion to immune function to glucose metabolism. Light is the primary signal that sets and synchronises that clock.
Natural light is more effective than artificial light in synchronising the biological clock with the environment — and when your biological clock is properly synchronised, your metabolism runs more efficiently. Your liver, skeletal muscles, and pancreas all have their own internal clocks, and they function best when those clocks are aligned with the natural light-dark cycle.
Chronic indoor living under artificial light disrupts this alignment — what researchers call circadian misalignment — and this disruption has been directly linked to impaired glucose metabolism, insulin resistance, and increased metabolic disease risk (Harmsen et al., 2025).
This means that eating outside in natural daylight isn't just a nice thing to do. It's a legitimate metabolic intervention — one that's free, requires no equipment, and works directly at the level of your mitochondria and your biological clock.
What I Actually Do
I try to eat at least one meal outside every day — usually lunch, because midday light contains the full spectrum of wavelengths including the red light that drives mitochondrial activity.
I also try to get morning sunlight exposure as early as possible — even just 10 minutes outside after waking helps set my circadian rhythm for the day, which has downstream benefits for blood sugar regulation, energy, sleep quality, and mood.
If you work indoors, opening a window or sitting near one during meals is a meaningful step — even sitting near a window rather than under overhead lighting makes a measurable difference to glucose dynamics.
And if you want to understand what's actually driving your symptoms — whether it's energy crashes, hormonal disruption, weight that won't shift, or persistent gut issues — blood sugar regulation is almost always part of the conversation.
A Note on the Research
The 2024 red light study used a specific 670nm light device rather than direct sunlight. Natural sunlight does contain these wavelengths — and is our best natural source of them — but I want to be transparent that the study conditions don't perfectly replicate eating lunch outside. The 2025 Cell Metabolism study is the stronger evidence for the direct benefits of natural daylight on blood sugar stability specifically.
Both studies are early in what is likely to become a much larger body of research. But the mechanism is sound, the risk profile is zero, and the intervention costs nothing.
How to Apply This
Eat at least one meal outside in natural daylight daily — lunch is ideal
Get morning sunlight exposure within an hour of waking — even 10 minutes makes a difference to your circadian rhythm
If you work indoors, position yourself near a window during meals
Reduce artificial light at night — this supports melatonin production, circadian alignment, and downstream glucose regulation
If you're dealing with energy crashes, hormonal symptoms, or unexplained weight gain — consider getting your fasting insulin and full iron studies checked alongside your standard bloods
Frequently Asked Questions
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Research suggests yes — natural sunlight contains red light wavelengths that stimulate mitochondria to use glucose more efficiently, and a 2025 controlled study found that people exposed to natural daylight had significantly more stable blood sugar levels throughout the day compared to those under artificial light. The effect is most pronounced with consistent daily exposure rather than occasional outdoor meals.
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Natural sunlight contains red light wavelengths (around 670nm) that increase mitochondrial membrane potential and ATP production. This increases cellular demand for glucose, meaning cells pull more glucose out of the bloodstream — resulting in lower, more stable blood sugar levels after meals. Sunlight also helps synchronise the body's circadian rhythm, which governs how efficiently glucose metabolism runs across the day.
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Insulin is a hormone, and when it's chronically elevated due to poor blood sugar regulation, it disrupts the entire hormonal system. High insulin suppresses SHBG, which increases free testosterone — a key driver of PCOS, acne, and androgen excess symptoms. It also dysregulates cortisol, impairs progesterone production, and disrupts the communication between the brain and ovaries. Blood sugar stability is foundational to hormonal health.
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Yes — blood sugar spikes drive systemic inflammation that directly affects the gut lining, increases intestinal permeability, disrupts the microbiome, and feeds opportunistic bacteria. Poor blood sugar regulation is also linked to impaired gut motility, contributing to bloating and digestive dysfunction.
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Morning sunlight is most important for setting the circadian rhythm, which has downstream effects on metabolism throughout the day. Midday sunlight contains the fullest spectrum of wavelengths including red light, making it the most beneficial time for direct mitochondrial stimulation. Even 10–20 minutes of outdoor exposure at either time appears to have measurable metabolic benefits.
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LED artificial lighting is heavily weighted toward blue wavelengths and lacks the red light content found in natural sunlight. Research suggests that blue-dominant light reduces mitochondrial function and may impair glucose metabolism over time. Spending most of the day under artificial lighting — which describes the lives of most modern adults — may be a significant and underrecognised contributor to blood sugar dysregulation.
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Common signs include energy crashes in the afternoon, sugar or carbohydrate cravings, brain fog after meals, difficulty losing weight especially around the abdomen, mood swings or irritability when hungry, poor sleep quality, hormonal symptoms like PMS or irregular cycles, and persistent fatigue. Many people with blood sugar dysregulation have normal fasting glucose results — fasting insulin and HOMA-IR are more sensitive markers.
WANT TO UNDERSTAND WHAT'S DRIVING YOUR SYMPTOMS?
If you're experiencing energy crashes, hormonal disruption, gut issues, or weight that won't shift — there is often more going on beneath the surface than standard testing reveals.
At Emba Wellness, I take a root-cause approach to your health — looking at your full symptom picture, your pathology, and the lifestyle factors that are either supporting or undermining your body's ability to function optimally.
I offer 1:1 consults in Melbourne and via telehealth across Australia. Let's get you some real answers.
About the Author
Jessica Diakoumakos | BHSc Naturopathy & BHSc Psychology Clinical Naturopath & Founder, Emba Wellness — Melbourne, Victoria, Australia
Jess is a Melbourne-based clinical naturopath and founder of Emba Wellness.
She specialises in:
Gut health — IBS, SIBO, bloating, microbiome repair, leaky gut
Hormonal health — PCOS, endometriosis, PMS, perimenopause, post-pill recovery
Functional pathology — interpreting blood tests through a root-cause lens
Energy & thyroid — Hashimoto's, fatigue, burnout, adrenal dysregulation
Immune health — autoimmune conditions, chronic inflammation, immune dysregulation
Her approach is evidence-based and deeply personal. Having managed her own Hashimoto's thyroiditis through naturopathic medicine, Jess understands first-hand what it feels like to be dismissed by conventional medicine — and what it feels like to finally get answers.
Emba Wellness offers naturopathy consultations via Telehealth, across Australia.
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Harmsen, J., Habets, I., Biancolin, A. D., Lesniewska, A., Phillips, N. E., Metz, L., Sanchez-Avila, J., Kotte, M., Timmermans, M., Hashim, D., de Kam, S. S., Schaart, G., Jörgensen, J. A., Gemmink, A., Moonen-Kornips, E., Doligkeit, D., van de Weijer, T., Buitinga, M., Haans, F., De Lorenzo, R., Pallubinsky, H., Gordijn, M. C. M., Collet, T., Kramer, A., Schrauwen, P., Dibner, C., & Hoeks, J. (2025). Natural daylight during office hours improves glucose control and whole-body substrate metabolism. Cell Metabolism, 38(1). https://doi.org/10.1016/j.cmet.2025.11.006
Diamanti-Kandarakis, E., & Dunaif, A. (2012). Insulin resistance and the polycystic ovary syndrome revisited: An update on mechanisms and implications. Endocrine Reviews, 33(6), 981–1030. https://doi.org/10.1210/er.2011-1034
Powner, M. B., & Jeffery, G. (2024). Light stimulation of mitochondria reduces blood glucose levels. Journal of Biophotonics, 17(3), e202300521. https://doi.org/10.1002/jbio.202300521
All content published on the Emba Wellness blog is written by Jessica Diakoumakos and is intended for educational purposes only. It does not constitute medical advice. Please consult a qualified health practitioner before making changes to your health care.
