How Cortisol Impacts Gut Health and the Microbiome

In a busy world, expectations to be high functioning and consistently keep up the pace leave many of us feeling overwhelmed and starved of time to rest. As a consequence, chronic stress is almost unavoidable and affects many of us more than we realise.

• 1 in 9 (11%) UK adults feel stress every day¹
• 74% of people feel so stressed they are overwhelmed or unable to cope²
• Stress-related inpatient hospital admissions in the UK are around 5.5 million, costing the NHS nearly £11 billion each year³

Stress symptoms are not always obvious, and they are not always permanent. But if chronic stress goes unaddressed, it can seriously affect physical and mental health through mechanisms linked to metabolism, gut health, digestion and even food choices.

What is stress?

Stress is an umbrella term for the body’s response to physical and psychological threats. It exists to protect us^4,5,6.

What happens in the body during times of stress

• Stress processes initiate in the nervous system
• The brain releases hormones that shape our response
• This triggers fight or flight, driving physiological changes to restore homeostasis (the body’s internal balance)^4,5,6.

Symptoms of acute stress include:

• Raised blood pressure and heart rate
• Hyperventilation and sweating
• Reduced digestion as blood flow is diverted away to more essential functions^7,8

These changes are largely driven by the hormones adrenaline and cortisol. When this response is sustained for long periods, it can impact long-term health.

Hormonal response to stress: adrenaline, cortisol and the HPA axis

During fight or flight, hormones adrenaline and cortisol are released to manipulate internal mechanisms and prioritise survival⁹.

Adrenaline (and noradrenaline)

• Drives physical symptoms such as raised blood pressure and heart rate
• Reduces digestion by redirecting blood away from digestive organs¹⁰

Cortisol (the stress hormone)

• Influences inflammation and metabolism
• Alters the breakdown of proteins and fats
• Raises blood sugar levels
• Reduces insulin sensitivity to increase the brain’s access to energy stores^{11,12,13,14,15}

Cortisol is released in the brain and regulated by the hypothalamic–pituitary–adrenal (HPA) axis¹¹. This can impact memory and focus^12,13 as well as emotional regulation¹⁴. This overlap helps explain why brain function, mental health and digestion often shift together during stress and why it can affect behaviour around eating.

These responses are useful short term, but if cortisol stays elevated for longer periods it can:

• Impact metabolism
• Promote weight gain
• Affect food choices
• Increase risk of diseases such as diabetes^16,17

What causes stress?

Stress is not only emotional. Anything that threatens homeostasis can trigger a stress response. Examples include:

• Loss of blood
• Traumatic pain
• Ill health

Everyday factors can contribute too, including:

• Eating foods that do not meet your needs
• Not drinking enough water
• Not getting enough sleep

All these factors can contribute to oxidative stress, which can damage cells within the body and increase signs of ageing and risk of disease^18,19,20,21.

With modern lifestyles, ongoing stress can accumulate and keep us in survival mode for longer periods. Over time this may:

• Increase irritability
• Promote emotional stress and burnout
• Reduce tolerance for further stress²²
• Predispose us to a higher risk of disease

Because stress can become normal, it is often harder to notice the symptoms until they have been present for a while.

Signs and symptoms of chronic stress

Chronic stress can affect people differently, but common patterns include the following.

Physical impacts

• Flare-ups of skin-related conditions such as acne and eczema
• Increased inflammation
• Muscle tension and nerve constriction, potentially leading to:
  • Reduced mobility
  • Pain
  • Delayed recovery
  • Further psychological distress^23,24

More serious consequences

• Chronically raised blood pressure and heart rate, increasing risk of cardiovascular disease
• Reduced sleep quality, contributing to sleep disorders and fatigue
• Reduced immune function and energy
• Increased risk of psychiatric disorders such as depression and anxiety²⁵

Stress can also affect metabolic health and nutritional status, increasing the risk of diabetes or malnutrition²⁶.

Recent studies suggest the gut may have more involvement in stress activation than previously realised. Gastroenterologists have observed that people with gut-related conditions such as inflammatory bowel disease (Crohn’s disease or ulcerative colitis) often experience flare-ups during periods of high emotional stress^27,28.

Gut-related impacts of stress

• Weight loss or weight gain
• Increased risk of gastrointestinal ill health
• Increased risk of diabetes or malnutrition²⁶

Stress and the gut–brain axis

The gut–brain axis is the bi-directional signalling between the brain and the gut that regulates gastrointestinal and cognitive processes and helps maintain proper function²⁹. We recognise this intuitively (for example, butterflies in the stomach), but the full picture, especially around nutritional intake and absorption, is complex and still developing.

Common appetite patterns during stress

• Some people lose appetite, likely linked to adrenaline’s effects on digestion
• Others gravitate towards energy-dense, dopamine-activating foods (high in sugar and saturated fats), possibly to support mood and emotional stability^30,31

Cortisol and the gut microbiome: what research suggests

The gut contains a complex community of microorganisms including bacteria, fungi and viruses, collectively known as the gut microbiome. These microbes are a key part of gut–brain communication and may even influence brain function and mood^32,33.

Gut–brain–microbiome interactions rely on nutritional input for optimal function. However, stress, particularly cortisol release, can disturb internal balance, including digestion^34,35.

Research suggests cortisol exposure may:

• Trigger inflammatory responses
• Alter the balance of beneficial and harmful gut bacteria^36,37
• Disrupt intestinal and microbiome homeostasis linked to:
  • Nutritional uptake
  • Hormonal transmission
  • Emotional processing^38,39

There is also evidence linking altered gut microbiota with increased emotional distress and lower thresholds for stress-related hormonal activation^40,41,42,43.

That said, research linking diet, psychological health and microbiome changes is still relatively limited. Practical advice usually comes from weighing current evidence alongside individual context.

Nutritional cortisol management: cravings and comfort foods

Ever wanted chocolate after a stressful day, or a takeaway because you feel you have earned it? That is not unusual to hear.

Under stress, we may be drawn to foods that feel comforting^44,45. While they may support mood in the short term, they are often low in nutritional value. Over time, this pattern can:

• Contribute to weight gain
• Cause fast but short-lived boosts in energy and mood
• Reduce physical and mental performance
• Add more stress to digestion^46,47

Cortisol can impact metabolism and may also reduce our ability to digest fat^16,17. Comfort eating can also come with guilt and negative self-image, further fuel for emotional stress⁴⁸.

This can create a loop: stress shifts food choices, and food choices can aggravate stress-related metabolic changes, raising long-term health risks^49,50. That is why it is important to understand how nutrition can affect stress (and vice versa) and how supportive routines can help manage risk.

Foods to support stress and gut health

We all know a healthier diet is beneficial, but what does that mean in the context of stress and cortisol?

Compared with a diet high in processed foods, a diet rich in whole foods such as fruit, vegetables, nuts and seeds may:

• Reduce oxidative stress
• Help manage stress-related changes in the gut microbiome
• Support psychological stress regulation^51,52,53

These foods provide:

• Vitamin C, vitamin E, flavonoids and polyphenols (antioxidants)
• Potential support for inflammation and emotional wellbeing^54,55,56,57
• Fibre to support digestion and gut health⁵⁸

In addition, people who eat more fruit and vegetables (versus higher meat intake) tend to have improved blood pressure and may be at lower cardiovascular risk, which is relevant because stress can worsen these risk factors⁵⁹.

Some studies also suggest prebiotics and probiotics may support a dysregulated microbiome and reduce stress, anxiety and/or depression^60,61,62.

Key takeaways for professionals

Stress impacts the body in multiple ways, but one of the biggest consequences is how it affects brain–gut communication, digestion and nutritional behaviour.

In practice

• Adrenaline and cortisol during stress can restrict digestion and shift metabolism
• Chronic stress can raise blood pressure and heart rate and increase risk of heart disease and diabetes, risk that can be influenced by dietary patterns
• Everyone is different; what supports one person may not be as effective for another
• Diets high in saturated fats, sugar and salt (common in processed foods) can aggravate stress and internal stressors
• Diets higher in fruit and vegetables and lower in processed foods and red meat may support stress recovery and emotional wellbeing
• Polyphenol- and vitamin-rich foods can help reduce oxidative stress
• Supplements can help fill gaps when diet alone is not meeting needs, but advice should be individualised

A commonly cited gold standard dietary pattern is the Mediterranean diet – high in fruit and vegetables, legumes and beans, nuts, seeds and wholegrains, with olive or other vegetable oils, moderate fish, white meat and dairy, and much lower red meat and processed foods. It is strongly linked with benefits for brain function, physical health and emotional wellbeing^63,64,65.

Nutritional advice for stress management should be given with caution. Consider existing health conditions and lifestyle factors, and encourage food diaries where helpful so cravings and symptoms can be tracked for a clearer, personalised picture.

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