The Short Version
The claim captures a partial biochemical truth — carbohydrates can promote tryptophan uptake and serotonin production — but the unqualified statement that evening carbs "have a calming effect" is misleading. Peer-reviewed evidence shows outcomes depend critically on carbohydrate type, quality, and quantity. High-glycemic or large carbohydrate meals before bed are associated with sleep fragmentation, melatonin suppression, and blood sugar disruption. Only high-quality, low-glycemic carbohydrates in moderate amounts show associations with improved sleep and reduced anxiety, and even then, the evidence is mixed on evening-specific timing.