According to results presented at the Annual Meeting of the Society for the Study of Ingestive Behavior (SSIB), test subjects were more satisfied for longer periods of time after consuming food of varying quantities for which they were led to believe that portion sizes were larger than they actually were.
Jeff Brunstrom from the University of Bristol also told attendees that memories about how satisfying previous meals were also played a causal role in determining how long those meals staved off hunger. Taken together, the results indicated that expectations before eating and memory after eating play an important role in governing appetite and satiety, he said.
Such data may have implications for food manufacturers, particularly from a labelling aspect, added the Bristol-based researcher.
“Labels on ‘light’ and ‘diet’ foods might lead us to think we will not be satisfied by such foods, possibly leading us to eat more afterwards,” said Dr Brunstrom. “One way to militate against this, and indeed accentuate potential satiety effects, might be to emphasize the satiating properties of a food using labels such as ‘satisfying’ or ‘hunger relieving’.”
The research was funded by the Biotechnology & Biological Sciences Research Council (BBSRC) and a consortium of food companies under a joint initiative with the Diet and Health Research Industry Club (DRINC).
Fat and brain changes
Also presenting at the SSIB, Mitchell Roitman from the University of Illinois at Chicago reported findings on how prolonged exposure to a high fat diet may be correlated with changes in the brain chemical dopamine within the a part of the brain linked to the reward system.
According to findings from studies with laboratory rats, ‘real-time’ changes in dopamine levels were observed in the striatum after animals consumed a high fat diet for either two or six weeks. Consuming a high-fat diet was associated with a reduction in the release of dopamine in lab rats, and a reduction in the reuptake by “dopamine transporters” within the striatum, compared with animals consuming a low fat diet.
“Previous research has demonstrated reduced dopamine transporter numbers in association with obesity and exposure to a high fat diet,” explained Roitman. “Our research shows that these changes lead to major differences in the way dopamine functions in the brain.”
The results from this study highlight the impact of diet on brain neurochemistry – and in particular on brain systems that regulate motivation and willingness to work for food reward in rats as well as humans.
The study was supported by the National Institute on Drug Abuse (NIDA).
Brain rewiring
This is not the first time that a high fat diet has been linked to changes in brain chemistry. Earlier this year, scientists from The Scripps Research Institute in Florida reported that the development of obesity was accompanied by a break-down in brain chemistry linked to pleasure responses. According to findings published in Nature Neuroscience, the very same changes occur when rats over-consume heroin or cocaine.
"These findings confirm what we and many others have suspected that overconsumption of highly pleasurable food triggers addiction-like neuroadaptive responses in brain reward circuitries, driving the development of compulsive eating," said lead researcher Dr Paul Kenny.