When you Feel Flat Over Christmas? That’s Not the Flu — It’s Your Diet

Every December, January and February, the same story repeats itself.

People feel exhausted. Their mood is low. Their digestion is off. They’re catching every cough and cold going. And the conclusion is always the same: “I need a pill.” “I need the GP.” “I need the flu jab.”

No. What’s needed is honesty.

Rich foods, ultra-processed meals, alcohol, chocolate, sugar, long nights indoors, disrupted routines, and increased stress all combine to place the body under pressure. Add in a lack of fibre and fresh, whole foods, and it’s no surprise that many people feel run down, lethargic, bloated, or plagued by coughs, colds, reflux, and digestive discomfort at this time of year.

Your immune system doesn’t weaken overnight—it reflects what you consistently give it. The body is simply responding to what it has been fed.

You Didn’t Catch a Bug — You Created the Conditions

The immune system doesn’t collapse randomly. Around 70% of it is linked to the gut, where trillions of microbes interact with immune cells daily (Belkaid and Hand, 2014). When the diet shifts towards refined carbohydrates, alcohol, additives, and minimal fibre—as it does over Christmas—beneficial bacteria are starved and inflammation rises.

Low microbial diversity weakens immune signalling, disrupts digestion, and increases susceptibility to infection. That’s why reflux, bloating, fatigue, and recurring illness peak after the festive season.

This isn’t controversial science. It’s established physiology.

Your Low Mood Isn’t Seasonal — It’s Gut-Driven

Here’s the uncomfortable truth: mental health is inseparable from gut health.

Approximately 90% of serotonin—the neurotransmitter associated with mood stability, calmness, and emotional resilience—is produced in the gut, not the brain (Yano et al., 2015). This process depends on a healthy, fibre-fed microbiome.

A low-fibre, high-sugar Christmas diet disrupts this system. Gut inflammation impairs signalling along the vagus nerve—the primary communication pathway between gut and brain—reducing vagal tone and contributing to anxiety, low mood, lethargy, poor digestion, and weakened immune responses (Cryan and Dinan, 2012; Carabotti et al., 2015).

So when people feel flat, unmotivated, anxious, and exhausted in January, it isn’t mysterious. It’s the downstream effect of dietary neglect.

Sugar, Dopamine & the Craving Trap

Then come the cravings.

Ultra-processed foods rapidly stimulate dopamine, the brain’s reward neurotransmitter. When fibre and micronutrients are lacking, the body seeks stimulation to compensate. Sugar, alcohol, caffeine, vaping, recreational drugs, energy drinks, and refined carbohydrates provide fast reward—but at a cost (Volkow and Wise, 2005; Hall et al., 2019).

This creates a loop: Low fibre → impaired gut signalling → reduced serotonin → increased dopamine-seeking behaviour → more sugar → more inflammation and fatigue.

This is not a willpower problem. It’s neurochemistry responding to deprivation.

Winter Light, Vitamin D & Why Supplementation Matters

There is one more variable people consistently ignore in winter: lack of daylight.

Short days dramatically reduce the skin’s ability to synthesise vitamin D, a hormone-like nutrient essential for immune function, inflammation control, muscle strength, and mood regulation. Low vitamin D status is associated with increased risk of respiratory infections, fatigue, and low mood—precisely the symptoms that peak in January (Calder et al., 2020).

Vitamin D does not work in isolation. Vitamin K2 is required to direct calcium to bones and teeth and away from soft tissue, making the combination of D3 + K2 both safer and more effective long-term.

At northern latitudes, food alone rarely provides sufficient vitamin D during winter. Sensible supplementation is not a luxury—it is a biological necessity when daylight is limited.

NOTE : When buying a winter supplement before the sun shines strong again, always purchase a D3 + K2 combination.

The Flu Jab Isn’t a Lifestyle Strategy

The flu jab is a targeted medical intervention. It is not a substitute for daily habits. It does not undo inflammation, repair the gut lining, restore microbial diversity, or reverse weeks of poor dietary input.

Health cannot be outsourced. It is built—or dismantled—daily.

Discomfort Is Feedback, Not Failure

What most people call “symptoms” are actually signals.

Fatigue is feedback. Brain fog is feedback. Cravings are feedback. Reflux, bloating, low mood, poor sleep—feedback. The body is not malfunctioning; it is communicating. Modern culture has simply taught us to silence these signals rather than listen.

Every year, the cycle repeats: overindulge, feel awful, seek a quick fix.

Stop Looking for Fixes. Start Creating Resilience.

A simple, appropriate 24-hour fast can help reset insulin levels, reduce inflammation, support cellular repair through autophagy, and give the gut time to recover (Longo and Mattson, 2014). Reintroducing real food—vegetables, fibre, healthy fats, fermented foods—allows the microbiome to do its job.

Where Fermented Foods Fit In

This is where traditional fermented foods play a valuable supporting role.

Tibico Fermentary’ s all-natural, lacto-fermented whole fruits and vegetables contain naturally occurring probiotics and postbiotics that can help:

• Support microbial diversity

• Improve digestion and gut barrier function

• Assist immune regulation

• Rebalance the acid gradient from mouth to large intestine

• Support energy levels through better nutrient absorption

  
  

Fermented foods have been consumed for thousands of years for good reason—they enhance food, they don’t replace it.

Importantly, they are not a magic solution. They must complement a balanced diet rich in vegetables, fibre, healthy fats, and adequate protein. You are the solution. Fermentation simply helps your body do what it is designed to do—more efficiently.

Take Responsibility for Your Health

Festive indulgence doesn’t have to mean festive illness. Small daily choices—adding fibre, reducing sugar, eating real food, supporting your gut—can make a measurable difference to how you feel, how often you get sick, and how quickly you recover.

The message is simple: We are what we eat—and our immune system reflects it.

References (Harvard style)

Belkaid, Y. and Hand, T.W. (2014) ‘Role of the microbiota in immunity and inflammation’, Cell, 157(1), pp. 121–141.

Carabotti, M., Scirocco, A., Maselli, M.A. and Severi, C. (2015) ‘The gut–brain axis: interactions between enteric microbiota, central and enteric nervous systems’, Annals of Gastroenterology, 28(2), pp. 203–209.

Cryan, J.F. and Dinan, T.G. (2012) ‘Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour’, Nature Reviews Neuroscience, 13(10), pp. 701–712.

Hall, K.D. et al. (2019) ‘Ultra-processed diets cause excess calorie intake and weight gain’, Cell Metabolism, 30(1), pp. 67–77.

Longo, V.D. and Mattson, M.P. (2014) ‘Fasting: molecular mechanisms and clinical applications’, Cell Metabolism, 19(2), pp. 181–192.

Makki, K., Deehan, E.C., Walter, J. and Bäckhed, F. (2018) ‘The impact of dietary fiber on gut microbiota in host health and disease’, Cell Host & Microbe, 23(6), pp. 705–715.

Volkow, N.D. and Wise, R.A. (2005) ‘How can drug addiction help us understand obesity?’, Nature Neuroscience, 8(5), pp. 555–560.

Yano, J.M. et al. (2015) ‘Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis’, Cell, 161(2), pp. 264–276.