The research team – led by associate professor Jennifer Nasser from Drexel University’s department of nutrition sciences in Philadelphia – used electroretinography (ERG) to measure dopamine in the retina in response to food stimulus. Retinal dopamine is normally released when the optical nerve responds to light, while release of dopamine in the brain is associated with expectation of reward.
Nasser said that experts usually thought of the two responses as quite separate, but when her team gave study participants 5 g of chocolate brownie in conjunction with light stimulus, the retinal dopamine release was significantly greater than when participants were given a sip of water with the same light stimulus.
“What makes this so exciting is that the eye’s dopamine system was considered separate from the rest of the brain’s dopamine system,” she said. “So most people – and indeed many retinography experts told me this – would say that tasting a food that stimulates the brain’s dopamine system wouldn’t have an effect on the eye’s dopamine system.”
The researchers also found the response was equivalent to the release of dopamine from stimulant drug methylphenidate (Ritalin).
Implications for food R&D
The study was small in scale, with just nine participants, but the researchers said that if the results could be replicated, they could prove a useful tool in the development of healthier foods.
“Food is both a nutrient delivery system and a pleasure delivery system, and a ‘side effect’ is excess calories,” Nasser said. “I want to maximize the pleasure and nutritional value of food but minimize the side effects. We need more user-friendly tools to do that.”
ERG is a widely used ophthalmological tool, which is non-invasive, quick, and relatively inexpensive, meaning it could have broad potential food and drink development if the study’s findings are validated. The researchers also said that the technique could help in the development of anti-obesity drugs.
(2013)Vol. 21, pp. 976-980 doi:10.1002/oby.20101
“Electroretinographic Detection of Human Brain Dopamine Response to Oral Food Stimulation”
Authors: J.A. Nasser, A. Del Parigi, K. Merhige, C. Wolper, A. Geliebter and S.A. Hashim