Blue Monday: what if our mood also played on the plate?

Every year, the third Monday of January is associated with Blue Monday, a concept popularized as the most depressing day of the year, and which often arouses some apprehension... If this concept is primarily based on a marketing equation, it nevertheless puts the finger on a very tangible reality: winter is a time conducive to morale drops. Less light, more fatigue, a sometimes unbalanced rhythm, a mental load that resumes after the holidays... All these factors influence our mood. But behind these feelings there are also specific biological mechanisms, notably related to neurotransmitters.

Mood: a matter of chemical messengers

Neurotransmitters are chemical messengers that allow neruones to communicate with each other. They play a key role in many functions: motivation, pleasure, stress management, sleep, concentration... and of course, mood.

Among them, two are particularly involved in our emotional well-being:

• Dopamine, associated with motivation, momentum, pleasure and reward

• Serotonin, often associated with emotional stability, calming, and mood regulation.

It is important to note that the link between these neurotransmitters and mood is complex and multifactorial: dopamine and serotonin influence certain aspects of our emotional state, but they do not determine mood in a simple and automatic way. Many factors, genetic, environmental, food, social, and related to the circadian rhythm, modulate their production and action.

When their balance is disturbed, some people may feel more easily fatigue, lack of motivation, irritability or a drop in mood; sensations that are common in the dead of winter, when light and physical activity are often reduced.

Serotonin: when the intestine influences the brain

It is often thought that everything happens in the head... yet, about 90% of serotonin is produced in the intestine. This intestinal serotonin does not cross the blood-brain barrier and therefore does not act directly on our mood. On the other hand, it would play an important role in digestion and in gut-brain communication via the vagus nerve in particular, which could therefore influence our well-being.

Recent research suggests that serotonin produced in the gut may influence emotional behavior via neural pathways like the vagus nerve, although these conclusions are mainly based on animal models and observational data in humans (Hung et al., 2025).

This production largely depends on the state of our intestinal microbiota, this ecosystem of billions of bacteria influenced by our diet, our stress, our sleep or even our lifestyle. Disturbances of this microbiota can therefore have indirect effects on mood and cognitive functioning (Fakhoury et al. 2025).

Another key factor: vitamin D, synthesized through exposure to natural light. In winter, decreased sunlight can contribute to a decrease in vitamin D, which can contribute to a less stable mood and increased fatigue.

Our emotional well-being therefore does not depend solely on our state of mind, but also on what is happening in our intestines and in our environment!

Neurotransmitters and biological rhythms

Our body follows a circadian rhythm, an internal clock that regulates physiological processes during the day, including the release of certain hormones and neurotransmitters.

• In the morning, dopamine is more active: it contributes to arousal, energy, and motivation

• In the afternoon, serotonin plays a role in mood regulation and can promote a sense of well-being.

• In the evening, part of serotonin is converted into melatonin, the hormone that prepares the body for sleep and regulates the sleep-wake cycle.

Natural light influences these processes: during the day, exposure to natural light stimulates the production of serotonin, while the decrease in brightness in the evening promotes the conversion of serotonin into melatonin. Respecting these rhythms, for example by maintaining sufficient exposure to light, a proper sleep schedule and physical activity, contributes to supporting emotional balance.

Diet as mood support

Neurotransmitters are made from precursors, nutrients found in our diet:

• Tryptophan, an amino acid, is a precursor of serotonin

• Tyrosine, another amino acid, is used to produce dopamine

Without going into biochemical details, the key idea is simple: what we eat provides the necessary building blocks for the synthesis of neurotransmitters. A diet that is too restrictive, unbalanced or even irregular can therefore, in certain situations, indirectly modulate our mental and emotional balance. However, it is important to emphasize that diet is not a miracle solution, but one lever among others to support the mood.

Breakfast and snack: allies of everyday life

Without seeking perfection (because no, it does not exist 😉), some advice can be applied on a daily basis.

Breakfast: a protein intake to stimulate dopamine

The role of breakfast is not only to "fill the stomach" after the night: it can help to start the day off on the right foot, both energetically and mentally.

• Why proteins? because they contain amino acids, like tyrosine (which as said previously is a precursor of dopamine). the latter is essential for motivation, concentration, and the feeling of pleasure. A breakfast rich in proteins (eggs, ham, dairy or protein-rich alternatives, oilseeds...) provides these necessary bricks in the morning, which could promote a more dynamic awakening and better attention.

• Integrate complete starches: They promote the release of energy in a gradual manner, which stabilizes blood sugar during the morning and avoids peaks of fatigue and inattention.

The afternoon snack: promote the synthesis of serotonin

Snacks often have the role of responding to hunger, or avoiding end-of-day cravings. Yet, here she has a different goal: to support mood, and stabilize energy between meals. Tryptophan is a precursor amino acid of serotonin, which we will therefore try to integrate into our snack.

• Where is tryptophan found? Tryptophan is an amino acid that is therefore found in protein source foods, such as dairy products, eggs, oilseeds, oleaginous grains, legumes, etc.

• Why add carbohydrates to the snack? Tryptophan circulates in the blood alongside other amino acids. The consumption of carbohydrates triggers insulin secretion, which promotes the absorption of competing amino acids in the muscles, leaving proportionally more tryptophan available to cross the blood-brain barrier and participate in the synthesis of serotonin. This association can contribute to better mood support.

Food is not everything

Finally, it is important to remember that mood is multifactorial. Diet can help, but it acts in synergy with:

• Natural exposure to sunlight

• Physical activity

• Sleep quality

• Stress management

• Social link

(and I surely forget others!)

Rather than looking for a single solution, it may be more accurate to see this winter period as an invitation to take care of oneself gently, without guilt 🤍

Bibliography

Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH. Effects of carbohydrates on brain tryptophan availability and stress performance. Biological Psychology. 2007;74(1):66–72.

Hanzawa F., Hashimoto M., Gonda M., Okuzono M., Takayama Y., Nagai N., & Yumen Y. (2025). High‑fat, high‑sugar breakfast worsen morning mood, cognitive performance, and cardiac sympathetic nervous system activity in young women. Food and Humanity, 5, 100900.

Hung LY, Alves ND, Del Colle A, et al. Intestinal epithelial serotonin as a novel target for treating disorders of gut‑brain interaction and mood. Gastroenterology. 2025;168(4):754–768. DOI:10.1053/j.gastro.2024.11.012.

Benton D, Brock H. Mood and the macro-nutrient composition of breakfast and the mid-day meal. Appetite. 2010 Dec;55(3):436-40. doi: 10.1016/j.appet.2010.08.001. Epub 2010 Aug 13. PMID: 20709125.