Are you an early bird or a night owl? Why daylight is good for you either way 

“Get outside first thing” or “wake up at 5 am” has become one of the most repeated pieces of wellness advice going. It sounds almost too simple to matter, but this isn’t just a nice ritual. It may be one of the most direct ways we can influence our circadian rhythm – with knock-on effects on our metabolism, sleep, mood and even our skin.  

Your body’s ability to process food changes depending on the time of day, and that internal clock is set largely by the light you get. Understanding one means understanding the other, which is exactly what we set out to explore. We spoke to five nutrition and circadian science experts to find out what happens when we get morning light right. 

Your body runs on light 

To understand why nutrition and light are so tightly linked, it helps to know what a circadian rhythm actually is. As Adriano Santos, MSc, a circadian rhythm researcher at the University of Oxford and registered nutritionist, explains, the term comes from the Latin circa (roughly) and dies (a day).   

Every single cell in our body contains this tiny clock gene mechanism, and they’re all communicating with each other

That includes the organs that matter most for nutrition: the gut, the liver, the pancreas, all running on their own internal timing.  

There’s a master clock in the brain, the suprachiasmatic nucleus, and thousands of smaller “peripheral” clocks in every organ. Dr Frank A.J.L. Scheer, PhD, a circadian rhythm researcher at Harvard Medical School whose work spans three decades in the field, describes it as an orchestra:

The master clock is in the brain; it acts as the conductor, setting the pace of all the other clocks. 

That master clock is set almost entirely by light, via special cells in the eye that send a “wake up, start the day” signal straight to the brain. The problem, as Scheer puts it, is that our peripheral clocks respond mostly to when we eat, not when we see light. If those two signals get out of sync, for example, bright light in the morning but a very late dinner, “your liver might be in Boston, but your central clock in Amsterdam.”   

That mismatch, multiple researchers agree, is where much of the modern metabolic trouble begins.  

What morning light does to your blood sugar and weight  

Scheer’s research has shown that people burn roughly 29 to 44 per cent more calories digesting an identical meal in the “biological morning” than in the biological evening, and that shifting meal timing later by four hours increases hunger and slows metabolism.   

Independent research on time-restricted eating backs this up: benefits for blood sugar and blood pressure appear almost exclusively when people finish eating earlier in the day, typically by 6pm.   

Give the same person the same sugary drink in the morning versus the evening, and the evening spike is dramatically higher. Most likely, that’s because our internal clocks are simply better at handling food earlier in the day, when the pancreas secretes more insulin in response to a meal.  

The first meal of the day 

If morning light sets the clock, what you eat once you’re up helps lock the rest of the day into place.  

Catherine Jeans, an ION-trained nutritional therapist, is careful not to overstate this: not everyone wakes up hungry, and forcing breakfast on someone with genuinely no appetite isn’t the point. But for most people, skipping it altogether can tend to backfire.  

Evidence does suggest that if we skip breakfast, this could cause poor blood sugar regulation throughout the day

And once blood sugar starts swinging, the knock-on effects are familiar: a spike in stress hormones, feeling more emotionally frayed, and stronger cravings for sugar, caffeine and salty, refined food. 

There’s a circadian angle here too. “

Eating patterns help to establish our internal body clocks, and if we skip meals and have erratic eating patterns, this might impact other aspects of our circadian rhythm, including sleeping patterns.

An irregular breakfast habit doesn’t just cost you blood sugar stability that morning; it can also unsettle the same clock Santos and Scheer describe, making good sleep harder to come by. 

“It’s small, consistent, daily habits that add up,” she says. 

The perfect breakfast  

Ask five different experts for their idea of the ideal first meal, and you’d expect five different answers. In this case, though, what’s striking is how much they agree. 

As for what that first meal should look like, Jeans’s advice is simple: eat at a regular time, sit down, relax and chew properly.  For her, a breakfast that supports steady blood sugar should contain adequate protein, low sugar, plenty of fibre and some healthy fats.  

The habits she sees derail people most often are eating porridge with no protein added, choosing a “low sugar” cereal that isn’t especially nutritious, drinking coffee instead of eating all morning, or wolfing down breakfast at a desk.  

Gordon takes a similarly protein-first approach: build up a Greek yoghurt and granola breakfast with a scoop of pea protein, nuts, chia and flaxseed, or go savoury with eggs, avocado and grilled mushrooms, tomatoes and spinach. A full English doesn’t have to be off the table either, so long as it’s grilled rather than fried, wholegrain sourdough instead of fried bread, beans and spinach added, halloumi or grilled chicken sausage instead of processed bacon. 

Peterson’s take is about proportion and timing rather than the plate itself: get 75 to 80 per cent of your day’s calories in before midday, whether through one generous breakfast or a breakfast and lunch that do most of the heavy lifting, with dinner kept light.  

Santos adds some flexibility: not everyone needs to eat within an hour of waking, and some people, particularly early risers, may do better holding off slightly. His own go-to breakfasts follow the same protein-and-fibre principles: a live yoghurt bowl with whey protein, flaxseed, chia and a prebiotic fibre blend, topped with banana and peanut butter, or a quick protein pancake of eggs, almond flour, chia and collagen powder, finished with berries. 

So, it there such a thing as the perfect breakfast? Perhaps not. But the consensus is clear: make it protein-forward, high in fibre, light on refined sugar; eat without rushing and at a broadly consistent time; and make it substantial enough to be genuinely nutritious, rather than an afterthought before your first coffee. 

How much of this do you have to do? 

Courtney Marie Peterson, a researcher and Associate Professor of Nutrition at Harvard who moved from physics into studying time-restricted eating, is practical about how far people actually need to take this.  

Her advice, from most to least demanding, is: if you can manage it, eat within an eight-hour window on the earlier side of the day. If that’s unrealistic, “eat breakfast like a king, lunch like a prince and dinner like a pauper”, loading most calories into the first half of the day.  

And if even that feels like too much, follow just one rule: don’t eat within three hours of bedtime. 

Peterson practises a version of this herself, eating within an eight- to ten-hour window from around 7.30am, with 75 to 80 per cent of her calories eaten by midday. Her broader message is that whatever pattern you eat on regularly, your body eventually locks into. Which is exactly why a small, sustainable change tends to beat an ambitious one that doesn’t stick. 

Her research also adds a piece to the light puzzle.  

For years, nutrition science has puzzled over why higher vitamin D levels are so consistently linked to better blood sugar control, even though clinical trials giving people vitamin D supplements directly haven’t found the same benefit. Peterson’s suspicion, which lines up with what Santos and Gordon describe, is that vitamin D in these studies may simply be acting as a marker of how much daylight someone is getting, rather than the active ingredient itself.  

It may be the light exposure doing the real work, not the vitamin. 

Beyond blood sugar: mitochondria and mood 

Layla Gordon, an ION-trained nutritional therapist specialising in cardiometabolic health, points to the effect of morning light on the mitochondria, the energy-producing part of our cells.  

Getting that first bit of sunlight, even if it’s just five or fifteen minutes, really helps to influence our mitochondrial activity,” she says, “and that’s so important for metabolic health and healthy ageing.

Catherine Jeans adds the mood and appetite angle. Early morning sunlight triggers the brain’s release of serotonin, “which is so important for our mood and mental health, as well as appetite control and digestive health.” Get that release right, and the knock-on effects ripple through the day: steadier energy, fewer sugar cravings, and better sleep that night, since serotonin is also the precursor to the sleep hormone melatonin. 

Making it work in the UK 

For anyone picturing a golden sunrise stroll on a beach, the practical reality of a British morning may feel like a let-down. The good news is that it doesn’t need to be sunny for this to work. Even on a cloudy winter morning, outdoor light typically measures around 5,000 lux, compared with roughly 200 to 300 lux from an indoor kitchen light.  

Just go outside, because even on a cloudy day, you’re getting far more than you would indoors.  

For darker winter mornings when there simply isn’t daylight to be had, a good circadian light box, roughly £100 and upwards, can help fill the gap. 

The window that matters most, according to Santos, is the first six to eight hours after waking. Getting outside during that stretch, even for a lunchtime walk rather than a dawn one, still counts. 

What about shift workers? 

Sunrise walks are a lovely idea if your day starts at 7am. But a huge number of people – nurses, airport staff, hospitality workers – simply can’t build their day around the sunrise. Both Scheer and Peterson were keen that this shouldn’t be glossed over. 

According to Scheer, the reality is that most night workers never fully adapt their internal clock to their schedule.

Most shift workers do not entrain their circadian system to their night shift work, meaning that they will still have increases in melatonin during the night… and changes in their regulation of energy expenditure and glucose tolerance.

Commuting home into daylight after a night shift resets the clock all over again, and even permanent night workers tend to revert to a normal sleep pattern on days off. 

There’s a silver lining, though. In a series of controlled studies, Scheer’s team found that restricting eating to the biological day, rather than whenever people happened to be awake, protected against the negative effects of circadian misalignment on blood sugar, cardiovascular markers and mood.   

“Food timing can actually be a helpful tool,” he says.   

The practical takeaway is to cluster meals around the daytime sleep period rather than eating through the middle of the night shift, keep fast-releasing carbohydrates to a minimum overnight, and avoid eating in the last few hours before “bedtime,” whenever that falls.  Scheer emphasises that further studies are needed to translate these fundamental findings to real-world shift work conditions. 

It doesn’t have to be all perfect 

Perhaps the most reassuring message across all these conversations is that this isn’t about rigid rules.  

Not everyone is an early riser, and that’s genuinely biological, not a failure of willpower. Some people carry gene variants that make them naturally later types, while shift workers face a different challenge altogether, since their body clocks often never fully adapt to working through the night.  

As Jeans puts it:

We have to follow what works for us, but we don’t have to do everything, every day. 

The simplest version of this advice is also the most doable: when you can, get outside within an hour or two of waking, even briefly, even under grey skies. Pair it with a nutrient-packed breakfast and let your body clock – and your digestion – do the rest.