Food-related visual stimuli increase ghrelin levels

The neuropeptide ghrelin is a major signal for food intake in various species including humans. After exogenous ghrelin administration feeding and body weight increase in rodents. In normal human subjects ghrelin administration increases self rated appetite and calorie intake and prompts the imagination of favourite meals. Ghrelin levels increase in humans before meals and decrease after meals regardless whether meal times were fixed5 or meals were initiated voluntarily. It is unclear so far whether ghrelin levels are affected by external cues like sight of food. We investigated the influence of pictures showing food compared to neutral pictures on ghrelin levels in young normal male subjects (n=8). The study consisted of two consecutive sessions with a one week interval. During each session blood for later analysis of plasma concentrations of ghrelin was collected between 08.15and 13.00 hours every 15min (between 10.30 and 11.30 every 10min). Breakfast and lunch was provided at 08.30, and 12.00 respectively. Pictures were presented on a computer screen from 10.30 for 15min (each 6s) showing neutral images during the first and food contents during the second session. As expected ghrelin levels increased before each meal and declined after meals. In addition, ghrelin levels during the 30 minutes interval following the presentation of pictures with food increased significantly compared to the 30 minutes interval before this presentation (+18%, p<.01). In contrast, after presentation of the neutral pictures ghrelin levels remained unchanged (+3%, p>.24, t-test for matched samples). The difference in the increases between the two conditions was significant (p<.01, t-test for matched samples). Our findings suggest that sight of food elevates ghrelin levels in satiated healthy volunteers.