The Effects of Palatable Sweet Ingesta on Human Responsivity to Heat Pain

Abstract

It is well known that the taste of sweet solutions produces a morphine-like analgesia in both rats and human infants, and under certain conditions, possibly in human adults. To further explore whether ingestion analgesia persists into human adulthood, the present study was the first to utilize contact heat, a method of pain induction used commonly in both behavioural and pharmacological studies with laboratory animals. Left arms of 120 university undergraduates were exposed to a hot-plate, with pain responsivity assessed both before and after consuming either nothing (control group), or foods that they rated previously as unpalatable (e.g., black olives), neutral (e.g., rice cakes), or palatable (e.g., chocolate-chip cookies). Pain responsivity was assessed with four pain measures: pain threshold, pain tolerance, and visual analogue scale (VAS) ratings of pain intensity and unpleasantness. Between-groups comparisons in 2 separate experiments revealed that women (but not men) who consumed a palatable food showed increased pain tolerance, relative to the nothing, unpalatable, or neutral groups. Collectively, these data support our previous findings that “palatability-induced analgesia” exists in human adults, at least in females. Moreover, the findings support contact heat as a suitable method for assessing ingestion analgesia to experimental pain with human adults.