Chrononutrition – how to synchronise your diet with your body clock?

The body clock and nutrition

The existence of the body clock (also known as the circadian rhythm), which regulates how the body functions depending on the time of day, is not a myth. The circadian rhythm lasts about 24 hours and involves a series of changes and processes in the body, such as the cyclic release of hormones, fluctuations in body temperature and blood pressure, and the sleep-wake cycle. The “master body clock” is located in the brain’s suprachiasmatic nucleus (SCN), but in fact, the human body also has various other clocks, known as peripheral clocks, which can function independently of the “master clock.” They are present in the tissues of various organs, such as the intestines, muscles, and pancreas.

The main factor regulating the body clock is light detected by the retina. The phases of the circadian rhythm are therefore divided into a light (daytime) phase and a dark (night-time) phase.

Here are some processes that take place in the body in line with the regular circadian rhythm:

• Glucose tolerance is highest during the day (in the light phase) and lower at night (in the dark phase).
• The level of melatonin (the sleep hormone) drops around 7:00 a.m. and rises around 8:00 p.m.
• The level of cortisol (known as the stress hormone) naturally rises in the morning (around 8:00 a.m.).
• Sleep deepens around 1:00 a.m., which is when the deep sleep phase most often occurs.
• Body temperature begins to rise around 3:00 a.m.

There are many factors that influence the body clock, and one of them is diet. The link between nutrition and the body clock is two-way: the body clock affects how the body processes different foods at different times, while food can also regulate the body clock. Any deviations from the “norm” related to eating, such as late-night overeating or skipping meals, can disrupt the body clock and disturb the circadian rhythm.

What is chrononutrition?

Chrononutrition (also called chrono-eating) is the science that studies and explores the links between the body’s circadian rhythm and food. Chrononutrition emphasises that the functioning of the body is influenced not only by what we eat, but also by when we eat. It is a relationship worth examining in two directions: the influence of the body clock on digestion and metabolic processes, and the impact of meal timing on the circadian rhythm (peripheral clocks). What we eat and when we eat can either synchronise the body clock or disrupt it and disturb the circadian rhythm.

The concept of chrononutrition was first described in 1986 by French doctor Dr Alain Delabos. He pointed out that eating late and having irregular meals was associated with an increased risk of obesity, impaired glucose management, and various cardiometabolic problems. He developed a set of rules aimed at improving nutrition by balancing meals in line with the natural circadian rhythm. His diet is based on following the body clock and the metabolic changes occurring within the 24-hour cycle, taking into account meal frequency, regularity, and timing. The key principle of Dr Delabos’ diet is to consume most of the daily calories and carbohydrates before lunchtime and to avoid a heavy evening dinner. Most calories should be consumed during the light phase of the daily cycle.

How does meal timing affect your body?

“Morning person”, “evening person” and their eating habits

The science of circadian rhythm officially distinguishes three human chronotypes:

•  The “morning” type refers to people who prefer morning activities and are most energetic in the early hours.
• The “evening” type refers to people who prefer evening activities and are most energetic later in the day.
• The “intermediate” type.

The body clocks of “morning people” and “evening people” can differ by as much as 2-3 hours, yet they remain rhythmic and cyclical.

Interestingly, scientific studies observing the lifestyle of people with different chronotypes have shown that those who prefer evening activity, the so-called evening person, are more likely to eat irregularly, skip meals (especially breakfast), consume fewer fruits and vegetables, and rely more often on energy drinks. This group is also statistically more likely to experience eating disorders.

Research also shows that “evening people” are more prone to various metabolic dysfunctions, obesity, and poorer glucose regulation. Scientists have estimated that this translates into a lifespan around 6.5 years shorter compared to those with a “morning” chronotype.

Circadian rhythm, food, and metabolism

Chrononutrition is rooted in various metabolic processes that occur with greater or lesser intensity throughout the daily cycle. Here are some of them, along with conclusions on how to plan your diet to make smart use of them for better health:

Post-meal glucose levels

• Circadian rhythm: Post-meal glucose levels rise higher after an evening meal compared to a meal eaten in the morning.
• Conclusion from chrononutrition: To avoid sharp spikes in glucose, carbohydrate-rich meals or the largest meals of the day are best consumed in the first half of the day. Heavy, high-carbohydrate meals with a high glycaemic load eaten in the evening can negatively affect glucose regulation.

Pancreatic activity

• Circadian rhythm: It has been shown that the activity of pancreatic beta cells (which secrete insulin) is about 15% higher in the morning than later in the day.
• Conclusion from chrononutrition: The body handles carbohydrate metabolism better in the first half of the day, so meals with a higher glycaemic load are best scheduled for that time.

Post-meal thermogenesis

• Circadian rhythm: Meals eaten in the evening generate significantly lower post-meal thermogenesis than those consumed in the first half of the day.
• Conclusion from chrononutrition: An evening meal may potentially provide more available calories than the same meal consumed in the first half of the day.

Read also: Thermogenic foods and thermogenics

Gastric emptying

• Circadian rhythm:  The rate of gastric emptying is faster in the morning than in the evening.
• Conclusion from chrononutrition: Meals eaten in the first half of the day are more likely to leave you feeling lighter than the same meals consumed in the evening.

Appetite-regulating hormones

• Circadian rhythm: Circadian rhythm disruptions may be linked to around a 38% increase in appetite due to elevated levels of ghrelin (the hunger hormone). This has been confirmed in studies involving shift workers.
• Conclusion from chrononutrition: Irregular eating and other activities that disrupt the circadian rhythm can lead to overeating and excess calorie intake. It is worth maintaining regular meal times, if your lifestyle allows.

Food, sleep, and recovery

According to the circadian rhythm, during the dark (night-time) phase, the body is best adapted to rest. After dusk, the secretion of melatonin, the sleep hormone, begins, making it easier to fall asleep and ensuring deep, restorative sleep. The moment when melatonin secretion begins is called DLMO (Dim Light Melatonin Onset). It is a physiological signal preparing the body for sleep, and it is best to avoid meals at that time.

Eating after melatonin secretion has begun and the body is preparing for sleep can disrupt the circadian rhythm. The body is already preparing for night-time rest, yet you give it extra “tasks” such as digesting food, releasing insulin, and distributing nutrients. Under such conditions, neither sleep nor digestion will function optimally. Glucose tolerance and fat metabolism are also impaired.

The last meal before sleep should also not be the largest meal of the day. This is not recommended either for night-time recovery or for digestion, glucose regulation, and maintaining a stable body weight. For dinner, a light meal with protein, a small amount of carbohydrates, and some healthy fats works best. Leave about 3-4 hours between your last meal and sleep.

Be sure to read: A diet that supports sleep and recovery and Natural sources of melatonin

Meal timing and a weight-loss diet

For a weight-loss diet to be effective, one basic condition must be met: a negative calorie balance must be created and maintained. In theory, for weight loss it does not matter whether you eat 500 kcal in the morning, in the evening, or in the middle of the night. In practice, however, the difference can be significant, as the same meal may affect you differently, for example:

• A heavy meal eaten too late will disrupt sleep, and sleep and recovery are crucial for the success of a weight-loss diet.
• If you eat too late in the evening while trying to break the habit of late-night snacking during weight loss, it may be harder to resist cravings.
• On the other hand, if you “use up” your daily calorie allowance too early in the day while on a weight-loss diet, you may simply feel hungry in the evening, making the diet harder to maintain.

Numerous studies confirm that when following a weight-loss diet, the most effective approach is to eat regular meals spaced throughout the day, for example every 3-4 hours. The largest meal is best eaten before the start of the “dark phase,” for example by 5 p.m. This approach not only aligns with the principles of chrononutrition but also makes it easier to stick to a weight-loss plan. One of the biggest enemies of a weight-loss diet is intense hunger: it arises when you eat too infrequently or too little. When it strikes, self-control mechanisms fail.

The benefits of eating meals at regular intervals, with an adequate break before sleep, are also confirmed by scientific research:

• A 2017 study by researchers at Harvard Medical School found that eating meals late in the evening or at night increased the risk of accumulating more body fat.
• A 2022 study by Vujović et al. showed that eating meals later led to disrupted hunger and satiety hormones (an increased ghrelin-to-leptin ratio) and even reduced calorie burning and body temperature. This can partly be seen as a “slower metabolism” after an evening meal compared to a morning one.
• It has also been shown that evening meals affect key metabolic pathways related to fat metabolism. Specifically, they increased adipogenesis (the formation of fat cells) and reduced lipolysis (the release of fat from cells). The authors of the study suggest that evening meals promote weight gain due to their impact on hormones, metabolic pathways, and gene expression.
• Researchers in Murcia studied people undergoing weight loss and divided them into two groups: those who ate their largest meal of the day before 3:00 p.m. and those who ate it after that time. Those in the earlier-eating group achieved significantly greater success in weight loss and also showed better insulin parameters.

Read more: “False friends” – healthy products that can sabotage your diet

Breakfast: yes or no?

Eating breakfast has been carefully studied for many years by nutrition researchers. Currently, there are two most common approaches to eating breakfast, and both have their advantages and disadvantages, as well as studies supporting the superiority of each option:

1. “Eat breakfast like a king” – the approach that recommends having a hearty breakfast, usually shortly after waking up.
2. “Eat breakfast when you feel hungry” – the approach that does not impose a specific time for having breakfast.

Scientific evidence leans towards the approach that recommends establishing a breakfast routine (though not necessarily immediately after waking up). Scientists have shown, for example, that:

• Eating a calorie-rich meal early in the day leads to higher energy expenditure throughout the day (increasing total daily energy metabolism).
• A regular breakfast routine is associated with better metabolic health (reduced risk of obesity, cardiovascular disease, and diabetes).
• People who eat breakfast are better at keeping their calorie intake closer to their needs when practising intuitive eating.
• People who eat breakfast regularly generally have better eating habits (including a lower level of processed foods in their diet and a smaller share of unhealthy snacks).

According to the principles of chrononutrition, it is definitely worth having calorie-rich meals in the first half of the day. They provide a steady supply of energy, prevent evening hunger spikes, and help maintain a healthy meal-timing routine. However, this is not the only correct option. You can have breakfast either immediately after waking up or a few hours later, while still maintaining its benefits based on chrononutrition principles and other scientific evidence. It is worth reflecting deeply on whether you delay breakfast because it genuinely makes you feel better, or whether you are masking hunger with coffee or not feeling it due to stress. This is a topic to consider individually or discuss with a dietitian.

Important! For athletes, eating breakfast is generally beneficial, and skipping it has drawbacks, such as reducing training performance, impairing recovery, or depleting muscle glycogen stores.

Tip from a dietitian: In practice, when advising nutrition patients, I do not stick to a single breakfast recommendation; each case is considered individually. Usually, for people who are “too busy to eat breakfast,” I recommend including it, as their reluctance often does not stem from a lack of hunger. For some individuals, consciously delaying this meal may work, provided it does not compromise the overall quality of their diet.

A practical approach to chrononutrition – dietitian’s tips

Here are some practical tips to help you apply chrononutrition knowledge in real life:

• Have your last meal about 3-4 hours before bedtime.
• Avoid eating large, late dinners. It is best to eat the largest meal of the day before melatonin production begins.
• Establish a regular meal routine that fits your lifestyle and stick to it. This helps support the maintenance of a consistent circadian rhythm.
• Ensure a sufficiently long overnight fast lasting at least 10 hours, ideally around 12 hours. A daily overnight fast aligns with the body’s natural metabolic rhythm.
• Consume most of your daily calorie intake in the first half of the day.

Important! The above tips work for most people, but there are some exceptions to these rules. Active individuals who train in the evening should not skip their post-workout meal because of the timing. For athletes, it is usually necessary to make individual adjustments to chrononutrition recommendations to fit their daily schedule, training plan, and goals.

How to maintain a healthy circadian rhythm?

To optimise your nutrition according to your body clock, you first need to maintain a healthy circadian rhythm. Regular eating habits help with this to some extent, but that is not all. Here are a few other key tips:

• Spend time in natural daylight during the day. Make use of natural light during the day: place your desk near a window and, whenever possible, take walks outdoors.
• Get exposure to sunlight after waking up. Step out onto a balcony, go for a walk, or simply look at the sky through a window. Morning exposure to natural light will help you get into an active mode.
• If possible, watch the sunset. The natural light at that time supports melatonin production.
• Avoid blue light in the evening. Limit the use of electronic devices with screens that emit blue light after dark, or at least 2 hours before bedtime.
• Make sure to stay physically active. Regular physical activity helps establish a healthy routine and improves the functioning of all body systems, including the hormonal and nervous systems.
• Set a consistent sleep schedule. Going to bed and waking up at consistent times makes it much easier to maintain a stable body clock.
• Avoid naps longer than 20 minutes, as they can disrupt your circadian rhythm.
• Avoid major deviations from your routine: try not to stay up late and respect your established daily schedule.

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