Cortisol
Cortisol is a vital steroid hormone produced by the adrenal glands, which sit just above your kidneys. Widely known as the body's primary "stress hormone," it acts as a chemical messenger communicating with almost every cell in your body [1]. While it gets a bad reputation for its link to chronic stress, cortisol is actually essential for life. It manages your sleep-wake cycle, reduces inflammation, and controls how your body uses macronutrients for energy.
What Does Cortisol Do in the Body?
Cortisol prepares your body to handle perceived threats by altering your metabolism and shutting down functions that are non-essential in a crisis. When your brain perceives danger, the Hypothalamic-Pituitary-Adrenal (HPA) axis triggers the release of cortisol. This instantly floods your bloodstream with glucose (sugar) to provide your muscles and brain with immediate energy.
| Bodily Function | Normal Cortisol Effect (Healthy) | Chronic Cortisol Effect (Unhealthy) |
|---|---|---|
| Metabolism | Efficiently converts fats and carbohydrates into usable energy. | Increases blood sugar levels and promotes the storage of visceral (belly) fat. |
| Immune System | Acts as a powerful anti-inflammatory to help heal injuries. | Suppresses the immune system, making you more susceptible to infections. |
| Digestion | Temporarily pauses digestion during acute physical activity or danger. | Leads to long-term digestive issues, including bloating and altered bowel habits. |
The Cortisol Awakening Response (CAR)
Cortisol levels naturally rise and fall in a 24-hour cycle dictated by your circadian rhythm. In a healthy individual, cortisol reaches its lowest point around midnight [2]. It then begins to build, peaking sharply about 30 to 45 minutes after you wake up [3]. This morning peak is known as the Cortisol Awakening Response (CAR) and is designed to give you the energy and mental alertness needed to start the day. If this rhythm becomes disrupted, you may experience extreme difficulty getting out of bed or feel wired and awake late at night [4].
Signs of High Cortisol Levels
Chronically elevated cortisol occurs when your nervous system remains stuck in a "fight or flight" state due to modern lifestyle pressures. According to recent surveys by the Mental Health Foundation, nearly three-quarters of UK adults report feeling so stressed they are overwhelmed or unable to cope [5]. This chronic psychological stress keeps the adrenal glands overproducing cortisol.
Common signs that your cortisol levels may be too high include:
- Unexplained weight gain: Particularly a stubborn accumulation of fat around the midsection and upper back.
- Sleep disruption: Difficulty falling asleep or waking up frequently between 2:00 AM and 4:00 AM.
- Severe fatigue: Feeling constantly exhausted despite getting a full night of sleep.
- Brain fog: Trouble concentrating, poor memory, and a general lack of mental clarity.
- Cravings: An intense desire for salty, sweet, or high-fat foods.
How Cortisol Affects Nutrition and Weight
Cortisol and nutrition share a two-way relationship. High cortisol drives physiological cravings for high-calorie foods because the brain believes it needs to replenish the energy "burned" during a stressful event. Furthermore, because cortisol increases blood glucose levels, it consequently triggers a release of insulin. High insulin levels signal the body to store excess glucose as visceral fat.
Dietary Strategies to Balance Cortisol
You can actively help your body regulate cortisol production through targeted dietary choices. Focusing on foods that stabilise blood sugar and support the nervous system is the most effective approach.
Additional Lifestyle Strategies That Can Help
In the video below Dr O'Donovan explains some simple lifestyle habits that can be used to manage cortisol.
Remember to always consult a medical professional before making significant changes to your diet or lifestyle to ensure it's being done in the most sustainable way.
Nutritionist's Corner: Final Thoughts
'Cortisol is not the enemy; it is the messenger. When we experience chronic stress, our bodies pump out cortisol to protect us, but this constant output disrupts our blood sugar and drives intense cravings for sugar and refined carbohydrates. From a nutritional perspective, the most powerful thing you can do to lower cortisol is to stop skipping meals. Eating balanced plates of protein, healthy fats, and fibre every few hours sends a signal of safety to your brain, turning off the alarm bells and allowing your nervous system to finally rest and digest.'
Yusra Serdaroglu Aydin, MSc RD
Sources
[1] Kaur J, Gandhi J, Sharma S. Physiology, Cortisol. [Updated 2025 Dec 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538239/
[5] 74% of UK overwhelmed or unable to cope at some point - Mental Health Foundation
Author
Yusra Serdaroglu Aydin, MSc RD
Head of Nutrition and Registered Dietitian
Yusra is a registered dietitian with a multidisciplinary background in nutrition, food engineering, and culinary arts. During her education, her curio...