on 20/04/2026
Dr Amy Hutchison, University of Adelaide
Have you ever wondered why you have lots of energy during the day, and feel sleepy at night? Or maybe you skipped breakfast and felt your stomach rumble loudly in class? This is all the work of your circadian rhythm, or body clock. Your biological clock collects information from the outside world, such as sunlight and temperature, and sets your body’s timing to match it. But your body clocks don’t just care about light and sleep — they also keep track of when you eat. Just like you feel more awake in the daytime and sleepy at night, your body is better at handling food at certain times of the day. This is where chrononutrition comes in — the science of how the timing of meals affects your health. Eating at the ‘wrong’ time, like late at night, can confuse your body’s clocks and make it harder for your system to use energy properly. My research works to understand how aligning our meals with our natural circadian rhythms can improve health, especially for people like shift-workers, who eat and sleep at different times of day.
What is a circadian rhythm?
Circadian rhythms are 24-hour patterns in processes within your body. This includes things like sleeping and waking, changes in body temperature, hormonal patterns, blood pressure, alertness, hunger and metabolism. “Circadian” originates from Latin; “circa” meaning “about” and “diem”, meaning “a day”, and refers to the 24-hour cycles that repeat every day, in a rhythmic pattern.
So why 24 hours? It is because the daily switch from light to dark tells your body clock what time it is. At the centre of your circadian system is a tiny “master clock” in a part of your brain called the suprachiasmatic nucleus, which we call the SCN for short (figure 1). The SCN is bossy, and it’s a bit like the school bell – it keeps all of the other organs in your body running to schedule, and makes sure that they do their jobs on time.
Figure 1: The master clock of the circadian system is located in a tiny part of the brain called the suprachiasmatic nucleus. It takes signals from light and relays them to the brain and peripheral clocks to determine sleep and wake cycles, as well as daily variations in alertness, hormone release, metabolism and body temperature. Peripheral clocks in other parts of the body send signals back to the master clock to give it more information about time of day. Food is a main time-keeper of rhythms in these organs. Even the bacteria in your poo have clocks in them!
Created in BioRender. Hutchison, A. (2025) https://BioRender.com/edll4n6
It’s not just humans that have circadian rhythms. Plants, animals, and even tiny bacteria all have circadian rhythms. Sunflowers turn their heads to follow the sun across the sky.
Light: The Timekeeper
So how does the SCN know what time it is, to keep everything running smoothly? The main signal is light. The SCN starts the waking-up process by detecting morning light through your eyes and sending signals to the brain that increase alertness. It triggers the release of hormones that make you feel energetic, and reduces production of melatonin, the sleep hormone. This chain reaction raises your body temperature and signals to your body that it is time to be awake and active.
At night, when it starts to get dark, your brain makes melatonin, which helps you feel sleepy. But here’s the catch: screens like TVs, tablets, and phones give off blue light. This can confuse your brain, and make it think it is time to be alert, so it slows down the production of melatonin. That’s why staring at a screen late at night can make it harder to fall asleep.
Your Body’s Hidden Clocks are EVERYWHERE!
Believe it or not, almost every cell in your body has its own little clock too. Even the bacteria that live in your intestines and in your poo have clocks! We call these clocks peripheral clocks, and they are important for relaying information BACK to the SCN about the time of day. Together, these clocks decide when you get hungry, when you feel strongest, and when it’s time to rest and repair. That’s why you might feel jet lagged after flying to a new time zone, confused when daylight saving changes, or why Monday mornings can feel rough after staying up too late on the weekend — your body’s clocks don’t like being thrown off schedule.
Food is a signal for circadian rhythms
Your peripheral body clocks don’t just pay attention to light. Light and dark are the most important signals for the SCN, but the peripheral clocks in other parts of your body care about when you eat. This is where chrononutrition comes in — the study of how meal timing affects your health.
Peripheral clocks in organs like your stomach and intestines, muscle, liver and pancreas send signals to the SCN to make sure everyone is on the same time schedule (figure 2). In this way, food can help the master clock keep time. Food intake is often thought of as a “zeitgeber”, which means “timekeeper” in German.
When you eat, meals send information to the brain, letting the body clock know it is time to turn on “food mode.” Once your body clock is in gear, it helps you digest and metabolise your food, using or storing all the energy you need. When digestion is finished, your body clock will go into “standby mode,” resting and waiting for the next meal. Most days, you probably eat meals and snacks at about the same times. So, at these times, your body clock and those organs will be ready to digest and metabolise. Then, at the times you are not eating (like during the night), your body clock will be able to recharge in standby mode.
Your body loves a routine
Research tells us that disrupting when you're eating versus fasting or sleeping and waking will change your circadian rhythm. This alters how the body processes nutrients from the diet. Think of it this way: your body is naturally better at using food for energy during the day, when you’re active and moving around. Eating late at night, when your body expects rest, can confuse your clocks. Instead of using the food for energy, your body is more likely to store it. For most people, their bodies get used to the same routine, and are better at doing different things at certain times of the day.
- In the morning, your body is naturally more alert. Your brain wants energy from food to get started. Your body is better at digesting and metabolising food earlier in the day than later.
- In the afternoon, your body temperature and muscle strength peak, making it a great time for sports. A lot of athletes set World Records in the afternoon!
- At night, your body starts slowing down, releasing melatonin (a sleep hormone) and preparing to rest. It is best to have your last meal around 2-3 hours before you go to bed, to allow time for your body to process it before you shift into sleep mode.
Eating in line with these rhythms helps your body process food more effectively. Eating against them — like snacking at midnight — can confuse your system. It’s normal to stay up late sometimes, especially on weekends, but if it happens often, it can confuse your body clock. Over time, always eating late at night and skipping meals during the day can affect your long-term health.
Early-birds and night owls
School-aged kids and teens are still growing, learning, and moving every single day. Eating at the right times can help with:
- Better focus in class: Breakfast fuels your brain after waking, so you can pay attention and solve problems.
- Stable energy levels: Eating regular meals gives you continuous energy throughout the day. When meals are skipped, delayed, or eaten too late, your body clock gets out of sync. This can make you feel sluggish, affect your mood, and even disturb your sleep.
- Sports and play: Snacks before exercise give your muscles quick energy for running, jumping, and playing.
- Healthy growth: A steady meal routine supports bones, muscles, and even your immune system.
- Teenagers run late. During puberty, our body clocks naturally shift later — that’s one reason teenagers often feel wide awake at night and sleepy in the morning. Avoiding screens late at night and ensuring teens eat a healthy breakfast in the morning can help them keep their circadian rhythm on track (figure 2).
Figure 2: Our bodies are good at doing different things at different times of day. Teenagers experience a natural shift in their circadian rhythm to later in the day compared to adults. This means the release of melatonin, the sleep hormone, tends to occur ~ 1 hour later, which is why they don’t feel tired until later at night. This also means they don’t feel alert until mid-morning. Limiting use of screens ( which emit blue light and suppress melatonin release) can support healthy sleep patterns and help them feel more alert at school.
Created in BioRender. Hutchison, A. (2025) https://BioRender.com/an9hpe7
Final Takeaway
Chrononutrition shows us that it’s not just what you eat, but also when you eat that matters. For kids and teens, eating in tune with your body clock helps you stay alert, have more energy to play and be active, grow stronger and healthier, and sleep better at night. For adults, it can help us manage our energy, be more active, improve our mood, and make work easier. So next time you reach for a midnight snack, remember: your body clock might be saying, “Save it for tomorrow!”.
Figure 2: Our bodies are good at doing different things at different times of day. Teenagers experience a natural shift in their circadian rhythm to later in the day compared to adults. This means the release of melatonin, the sleep hormone, tends to occur ~ 1 hour later, which is why they don’t feel tired until later at night. This also means they don’t feel alert until mid-morning. Limiting use of screens ( which emit blue light and suppress melatonin release) can support healthy sleep patterns and help them feel more alert at school.
Created in BioRender. Hutchison, A. (2025) https://BioRender.com/an9hpe7
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