Blood sugar and energy throughout the day go hand in hand
Everyone knows it. Full of energy in the morning, barely able to keep your eyes open after lunch, and around four in the afternoon an irresistible craving for something sweet kicks in. This isn't just a matter of willpower or bad habits – behind these fluctuations lies a very specific physiological mechanism that operates continuously in every human body. Blood sugar levels and energy throughout the day are closely connected, and understanding this relationship can fundamentally change how you feel from morning to evening.
Glucose is the primary fuel for both the brain and muscles. Without it, the body simply wouldn't function. The problem arises when blood sugar levels – medically referred to as glycaemia – fluctuate too much. A sharp rise after a sweet meal or white bread is followed by an equally sharp drop, and it is precisely in this drop that the cause of afternoon fatigue, irritability, or inability to concentrate lies. Stable blood sugar levels aren't just a concern for diabetics – they are the foundation of daily wellbeing for each and every one of us.
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How glycaemia affects energy from morning to evening
The human body is a perfectly designed system that constantly strives to maintain balance. Blood sugar levels should remain approximately between 4 and 6 mmol/l when fasting, rising briefly after meals before returning to normal. This return is managed by insulin – a hormone produced by the pancreas that helps cells utilise glucose. However, when someone has breakfast consisting of sweet cereal, white toast with jam, or sweetened yoghurt, they send a large amount of sugar into the bloodstream all at once. The pancreas responds with a massive release of insulin, which rapidly drops the blood sugar level – sometimes even below the optimal value. And this is precisely where the problem begins.
This phenomenon, sometimes called reactive hypoglycaemia, causes fatigue, brain fog, and a strong craving for more quick sugar. The body calls for immediate help, the brain sends a signal of hunger or a sweet craving, and the cycle closes. The person reaches for a biscuit or energy drink, blood sugar spikes again, insulin brings it back down – and the carousel continues all day. It's no wonder that after such a day, exhaustion arrives in the evening, even if the person hasn't done anything physically demanding.
Research repeatedly confirms that glycaemic fluctuations have a direct impact on cognitive function, mood, and physical performance. A study published in the scientific journal Nature Metabolism showed that even in healthy individuals without a diabetes diagnosis, significant glycaemic fluctuations are associated with worse mood, greater fatigue, and reduced ability to concentrate. In other words – what we eat and when we eat it literally shapes how we feel and how we perform.
Interestingly, two people can eat exactly the same meal and their glycaemic response will be completely different. It depends on the gut microbiome, genetic makeup, level of physical activity, and sleep quality. This is precisely why general recommendations are sometimes insufficient, and an individualised approach to nutrition is becoming increasingly important. Nevertheless, there are principles that apply to the vast majority of people and whose adherence demonstrably contributes to more stable energy throughout the day.
One of the key factors is the composition of meals. Foods rich in fibre, protein, and healthy fats slow down the absorption of glucose into the bloodstream, thereby preventing sharp fluctuations. Whole grains, legumes, nuts, seeds, vegetables, and quality proteins – these are the building blocks of a diet that supports stable glycaemia. Conversely, refined carbohydrates, sweetened drinks, and industrially processed foods act as direct triggers of glycaemic chaos.
Take Martina, a thirty-year-old teacher from Brno, as an example. For years she started her day with sweet cereal and coffee with sugar, around eleven in the morning fatigue and hunger would set in, for lunch she had pasta with sauce, and in the afternoon she couldn't get through without chocolate or coffee. In the evenings she was exhausted, yet still couldn't fall asleep. When, on the advice of a nutritionist, she switched to a breakfast consisting of eggs, vegetables, and wholegrain bread, the change came surprisingly quickly. Within two weeks she described significantly more stable energy, fewer sweet cravings, and better concentration during lessons. Her story is not exceptional – thousands of people who consciously work on stabilising their glycaemia share similar experiences.
Practical steps towards stable blood sugar levels
There is no need to count every gram of carbohydrates or give up everything that tastes good. It's more about understanding the basic principles and gradually introducing them into everyday life. The order of foods on the plate plays a greater role than it might seem – scientific findings suggest that consuming vegetables and protein before carbohydrates can significantly reduce the glycaemic rise after a meal. Research published in the journal Diabetes, Obesity and Metabolism showed that the order of food alone – first vegetables, then protein, finally carbohydrates – reduces postprandial glycaemia by up to 73% compared to the reverse order.
Movement is equally important. A short walk after a meal – just 10 to 15 minutes – helps muscles utilise glucose from the blood without the need for insulin. This simple habit, particularly popular in Mediterranean cultures, has a surprisingly powerful effect on the glycaemic curve after eating. It's not just a romantic tradition – it's functional physiology.
Another aspect that tends to be underestimated is sleep. A single night of sleep shorter than six hours can impair insulin sensitivity in a way comparable to a prediabetic state. A sleep-deprived brain craves sugar – and that's not a metaphor. Lack of sleep increases levels of ghrelin, the hunger hormone, and decreases levels of leptin, the satiety hormone, so the next day a person naturally reaches for more calorically dense and sweet foods. Sleep and blood sugar levels are therefore communicating vessels that cannot be viewed separately.
Stress represents another hidden factor. Cortisol, the primary stress hormone, raises blood sugar levels by mobilising glucose as an energy source for dealing with a threat. This was evolutionarily advantageous when a person had to flee from a predator. In today's world, however, chronic stress from work, finances, or interpersonal relationships causes cortisol to remain elevated long-term – and with it, glycaemia. As diabetologist and popular nutrition author Dr. Mark Hyman aptly noted: "Glucose is not just a number on a monitor – it is a mirror of how we live."
Intermittent fasting and the length of the break between dinner and breakfast also deserve special attention. The body needs time without food intake to regenerate, process glycogen stores, and improve insulin sensitivity. An interval of at least 12 hours between the last evening meal and the first morning breakfast is natural and beneficial for most healthy people. This isn't about drastic fasting – it's enough, for example, to have dinner by seven in the evening and breakfast after seven in the morning.
Natural dietary supplements and functional foods can also play their part. Cinnamon, chromium, magnesium, or berberine extract are among the substances for which scientific studies suggest a positive effect on glycaemic regulation. This is not a replacement for a balanced diet, but a suitable complement for those who want to support their body comprehensively. Likewise, green foods rich in chlorophyll, such as spirulina or young barley, contribute to overall metabolic balance.
It is also important not to forget hydration. Dehydration increases the concentration of glucose in the blood, because the blood is literally thicker. An adequate intake of pure water – approximately 30 ml per kilogram of body weight per day – is one of the simplest and most affordable ways to support stable glycaemia. Yet it is one of the most frequently overlooked factors.
This entire mosaic – meal composition, food order, movement, sleep, stress, hydration, and where appropriate, targeted supplementation – together forms the foundation for an energetically balanced day. It doesn't have to be about perfection, but about conscious decision-making and the gradual building of habits that give the body what it truly needs. People who begin to pay attention to how specific foods affect their energy and mood very quickly discover that the relationship between blood sugar and everyday vitality is far more straightforward than it seemed.
Glycaemia is not just a number for doctors and diabetics. It is a living indicator of how the body copes with everyday demands. And at a time when chronic fatigue, irritability, and mood swings are becoming almost the norm, it is worth considering whether the cause might be hidden precisely there – in blood sugar fluctuating between breakfast, lunch, and dinner. Small changes in diet and lifestyle have the potential to transform not only how much energy a person has, but also how they experience each and every day.
