Are you a cup-half-full or a cup-half-empty kind of person?
I’m the former, so naturally, this is how I feel when I think about sunlight. In the winter, even though there is less daylight compared to summer, once the Winter Solstice arrives, I acknowledge (and celebrate) the fact that our days are gradually getting longer – bringing us closer to those long summer nights for which many of us live.
Sunlight’s significance is quite astounding. Not so coincidentally, it’s one of the reasons I chose the name of my clinic: Soleil, a French word meaning sun. It’s the true ruler of all our biochemical processes, whether we’re actively aware of it or not – and many of us aren’t. We’re busy living our lives: rushing from here to there, playing taxi to our kids’ never-ending sports schedules, and attending a laundry list of obligations.
Regardless of the hustle and bustle, one thing remains constant and governs all our internal systems: the light–dark cycle. This is known as the circadian rhythm.
What Is This Rhythm, Really?
Circadian comes from the Latin circa diem, meaning “about the day.” This refers to the nearly 24-hour cycle to which the body is attuned. This cycle is largely influenced by light and darkness, which helps explain why most of our sleep schedules mirror the natural environment. While we can’t see these biological processes happening in real time, we can certainly feel them: alertness, fatigue, hunger, fullness, weight gain, or weight loss. That’s right – the governors of our daily habits are ruled by the sun.
When we wake in the morning and expose ourselves to sunlight, it signals the rest of the body that we are, in fact, awake. Being awake comes with very different biological demands compared to sleep, so this communication is critical.
We’re familiar, at least somewhat, with the hormone cortisol. Functionally, cortisol begins to rise around 3 a.m., with peak concentrations between 7 and 9 a.m. While this rhythm runs largely on autopilot, sunlight exposure reinforces the process – a synergism not unlike checks and balances.
Just as sunlight reinforces the cortisol rhythm, the prolonged absence of it can entrain a different one. This may look like a shift worker who sleeps during the day or a teenager on summer break who sleeps late into the morning. Despite the human body having its own internal “user manual,” the inputs, patterns, habits, and behaviors we dictate – as the ones in charge – can override these systems, for better or for worse.
What’s remarkable is how quickly the body responds when we begin to respect this rhythm again. Even a single morning spent outside – feeling light on your face instead of the glow of a screen – can shift appetite, mood, and energy by evening. These changes aren’t psychological tricks; they are natural, biological adjustments. The body is constantly waiting for clear signals about when to be awake, when to rest, and when to digest, and sunlight remains the most honest messenger we have.
Plot Twist!
The primary brain structure responsive to sunlight is the suprachiasmatic nucleus, or SCN—our central clock. And as with any central system, there are auxiliaries; these are known as peripheral clocks. While they take their cues from the SCN, they also exert influence within their own regions of the body. Two of the most influential – and most within our control – reside in the liver and the gut.
While light is the dominant zeitgeber, or external cue used by the SCN to calibrate time, it isn’t the only one. There are also non–light-related cues: the everyday inputs we provide that either reinforce or challenge our circadian rhythm.
The second most influential of these cues is…eating. This includes what we eat, when we eat, and how often. Many of us – fortunate enough – eat at least once a day, but what happens within that window is crucial to our biology.
To understand just how much daily habits influence physiology, consider your own routine. What do you do most consistently, regardless of work or kids’ schedules? Obligations tend to occur on predictable timelines and are easily reinforced. “Jennifer’s volleyball game on Thursday? 6 p.m. sharp.” It goes on the calendar, and you show up. If external factors can so reliably shape our schedules, why wouldn’t they do the same to our internal biology?
Intentionally choosing not to eat – what a privilege that must be. Dietary fads tend to leave lasting impressions – they cause a stir, fade, but never fully disappear – often resurfacing under a new name.
Fasting is one of those fads. Caloric restriction is another. While each may produce short-term results, in the long term, they often work against our physiology.
To clarify: Hormones are chemical messengers, communicating with one another to orchestrate specific outcomes. This matters because digestion – hunger, fullness, and satiety – is hormonally driven. Ghrelin is the hunger hormone; she lets us know when it’s time to eat (and don’t mess with her – she can get hangry). Leptin is the fullness hormone; it signals when it’s time to stop eating and explains why we can’t indulge indefinitely. Together, these hormones determine whether digestion is functional or dysfunctional based on inputs from the sunlight, but also from our routine and habits.
What Does Dysfunction Look Like?
You wake up around 6:30 a.m. – exhausted – and instead of exposing yourself to the natural sunlight peering through the window (or not so much during these winter months), you grab your smartphone and scroll mindlessly. You soon realize it’s closer to 7:30 a.m. and think, “There’s not enough time in the day.”
Your employer expects your arrival around 8:30 a.m., leaving little time to make breakfast. Instead, you head to the coffee shop drive-through and order an Americano. The coffee curbs your appetite until late morning, when you oblige lunchtime. With no time to prep, you head to the cafeteria and choose the salad bar – it’s the healthy option, right? This carries you until about 2 p.m., when energy dips and you reach for the coffee pot.
Dinner becomes your largest meal of the day. It includes protein, a starchy vegetable, and a leafy green. Afterward, it’s the couch – sports, Real Housewives, or finishing leftover work. Around 9 p.m., the chocolate craving hits. A few hours later, you’re in bed, tossing and turning until about 1 a.m., only to repeat the cycle the next day.
What This Is and Is Not
This is not a smear campaign, nor a critique of how people live their lives. Rather, it’s a mirror reflecting a pattern many Americans find themselves in regularly. These repeated habits gradually lead to physiologic breakdown. So when weight gain seems sudden, or a new diagnosis appears at a routine doctor’s visit, we shouldn’t be surprised.
What to Do Instead
Without knowing an individual’s specific concerns, these recommendations are foundational and often serve as a starting place.
Keep waking and bedtime consistent day to day, with no more than a one or two-hour deviation (including weekends). Aim for a bedtime well before midnight. For example, 10 p.m. to 6 a.m. is preferred over midnight to 8 a.m., even though both technically provide eight hours.
On rising, make mornings easier – use an alarm clock and keep your phone out of the bedroom. If you need it overnight, place it across the room so you have to get up. Once awake, expose your eyes to natural light first, before grabbing your phone.
Eat breakfast. If you’re not hungry, start small and begin the retraining process. Choose savory options (eggs, meat, yogurt) over sweet ones (pancakes, French toast, tropical fruits). Then have your coffee.
Eat lunch. Include carbohydrates here to fuel the rest of the day, paired with protein and fat to avoid a crash. When the 2 o’clock slump hits, eat before reaching for more coffee. Food is fuel – you’re tired because you’re under-fueled, not under-caffeinated.
If you must skip a meal, make it dinner. Research shows that front-loading calories earlier in the day – particularly at breakfast – supports greater weight loss compared to heavier dinners.
Understimulate at night. Avoid bright overhead lights, opting for dim lamps or low-light nightlights instead. If devices are necessary, use blue-light blockers or screen filters.
With time, sugar cravings will fade, sleep will improve, energy will increase, and overall mood will feel noticeably brighter.
Dr. Lyndsey Maher, ND, MSAc, is a naturopathic physician and founder of Soleil Acupuncture and Naturopathic Wellness in Hamden, CT. With specialties in acupuncture, hormone health, and holistic aesthetics, she combines evidence-based therapies with individualized care to help patients optimize their health from the inside out. She is passionate about empowering individuals and entire organizations to take an active role in their well-being; blending the best of science and natural medicine to create lasting, meaningful change. Call 203.871.3262.
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