Coffee on an empty stomach and cortisol: A dietitian’s take
"Should I stop having coffee on an empty stomach because it spikes my cortisol?" This is one of the most common questions I hear in clinic, thanks to a wave of social media content. Here is my take as a dietitian.
For regular coffee drinkers, the cortisol effect is much smaller than social media suggests. What matters more is whether your coffee is replacing breakfast.
Cortisol is a normal hormone that helps you wake up and feel alert. It naturally rises in the morning, whether you drink coffee or not.
Caffeine can raise cortisol, especially in people who do not usually drink it. But your body adapts. In one study, people who had caffeine daily showed no cortisol rise after their morning dose, while those who had gone without caffeine showed a clear rise.1 In other words, if you have coffee most days, your morning cup is unlikely to cause the "spike" you see online.
A short rise in cortisol is also not harmful in itself. It is part of how your body responds to everyday things, like exercise or a busy morning.
Cortisol and feeling jittery are not the same thing
The jittery or anxious feeling some people get from coffee comes mainly from caffeine's effect on the brain, rather than cortisol. It is more likely when you have a lot of caffeine,2 and people who live with anxiety tend to be more sensitive.3 If you notice this, cutting back may help.
Ever noticed coffee pushes your hunger back? Research suggests caffeine may slightly reduce how much you eat at your next meal, although the effect is small and short lived.4
The real issue is when coffee leads to skipping breakfast. This can mean:
- Missing a morning meal that helps keep your blood sugar and energy steady, which can be especially important for people with PMOS (previously PCOS)
- An energy dip mid morning, often leading to more coffee
- Stronger hunger later in the day
- Falling short on nutrients like protein, fibre, iron and calcium
For women, regularly not eating enough can also affect hormones and menstrual cycles.
Coffee and your gut
Coffee gets your gut moving and increases stomach acid, so it can affect people with reflux or IBS differently.
Reflux: Research suggests coffee does not cause reflux disease in most people.5 However, many people who already have reflux find coffee makes their symptoms worse, especially on an empty stomach.
IBS: Coffee can speed up how quickly things move through the bowel, sometimes within minutes.6 For some people with IBS, particularly those prone to diarrhoea, this can trigger symptoms. Others tolerate it well, so it is not something everyone with IBS needs to avoid.
If coffee on its own does not sit well with you, that is worth listening to.
Coffee and iron
Coffee can reduce how much iron you absorb from a meal. In one study, a cup of coffee with a meal reduced iron absorption by 39%, while coffee an hour before the meal had no effect.7 If your iron is low, leaving about an hour between coffee and iron rich meals or supplements can help.
How much caffeine is okay?
Health Canada suggests up to 400 mg of caffeine a day for most adults, and up to 300 mg if you are pregnant, breastfeeding or planning a pregnancy.8 A regular brewed coffee has around 100 to 180 mg, but café sizes vary a lot.
- Have your coffee with or after breakfast, rather than instead of it.
- If coffee irritates your gut, it is often better tolerated alongside food.
- If your iron is low, space coffee about an hour from iron rich meals.
For most regular coffee drinkers, the cortisol "spike" is not something to worry about. The bigger question is what your coffee is replacing. Pairing it with breakfast is a simple way to support steadier energy and better nutrition through the day.
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References
1. Lovallo WR, Whitsett TL, al'Absi M, Sung BH, Vincent AS, Wilson MF. Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosom Med. 2005;67(5):734-739. PMID: 16204431.
2. Liu C, Wang L, Zhang C, Hu Z, Tang J, Xue J, Lu W. Caffeine intake and anxiety: a meta-analysis. Front Psychol. 2024;15:1270246. doi:10.3389/fpsyg.2024.1270246.
3. Klevebrant L, Frick A. Effects of caffeine on anxiety and panic attacks in patients with panic disorder: a systematic review and meta-analysis. Gen Hosp Psychiatry. 2022;74:22-31.
4. Schubert MM, Irwin C, Seay RF, Clarke HE, Allegro D, Desbrow B. Caffeine, coffee, and appetite control: a review. Int J Food Sci Nutr. 2017;68(8):901-912. PMID: 28446037.
5. Kim J, Oh SW, Myung SK, Kwon H, Lee C, Yun JM, Lee HK. Association between coffee intake and gastroesophageal reflux disease: a meta-analysis. Dis Esophagus. 2014;27(4):311-317. doi:10.1111/dote.12099.
6. Saygili S, Hegde S, Shi XZ. Effects of coffee on gut microbiota and bowel functions in health and diseases: a literature review. Nutrients. 2024;16(18):3155.
7. Morck TA, Lynch SR, Cook JD. Inhibition of food iron absorption by coffee. Am J Clin Nutr. 1983;37(3):416-420. PMID: 6402915.
8. Health Canada. Caffeine in foods. Government of Canada.
