When a person skips breakfast or drinks only caffeine, their blood sugar may drop, leading to an increase in cortisol levels as a physiological response.
Evidence from Studies
Supporting (3)
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Caffeine Stimulation of Cortisol Secretion Across the Waking Hours in Relation to Caffeine Intake Levels
This study found that drinking caffeine makes your body release more cortisol, a stress hormone—even if you haven't had caffeine for a few days. It doesn't test skipping breakfast, but it does show caffeine alone can trigger this response.
Cortisol responses to mental stress, exercise, and meals following caffeine intake in men and women.
This study found that drinking caffeine makes your body release more cortisol, a stress hormone — even without skipping meals. So yes, caffeine alone can trigger this response, which matches part of the claim.
When you eat breakfast, your body lowers a stress hormone called cortisol. If you skip breakfast, that hormone doesn’t drop like it normally would, which means your body stays in a more stressed state — this matches the claim.
Contradicting (1)
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This study found that skipping breakfast actually led to lower morning cortisol levels in pregnant women, not higher—as the claim suggests. It also didn’t check if blood sugar dropped, so we can’t say hypoglycemia caused any change.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.