The study – published in Appetite – examined the motivational, neurochemical, and metabolic effects of a high fat diet in young male rats, after previous research had found that moderately high fat diets increase motivation for sucrose intake in adult rats.
Led by Dianne Figlewicz from the University of Washington, the team found that a high fat diet increased motivation for sucrose in the young rats. They said the increased sucrose intake was independent of metabolic changes or alterations in certain neurotransmitter metabolites.
However, they said that levels of a signalling molecule known as Agouti-related peptide (AGRP) were raised in the hypothalamus – a brain region that controls metabolism and influences hunger, thirst, fatigue and sleep patterns.
“A moderately high fat diet consumed during the peri-pubertal period (just before, during, and just after the age of transition into puberty) significantly increased motivation for sucrose solutions,” explained Figlewicz and her colleagues.
“We [also] demonstrated that increased activation of AGRP neurons is associated with motivated behaviour, and that exogenous … AGRP administration resulted in significantly increased motivation for sucrose,” they added.
The team suggest this increased expression and activity of AGRP in the hypothalamus could underlie the increased responding for sucrose caused by a high fat diet, and also suggest that changes in eating behaviours can drive metabolic alterations that lead to obesity.
“The enhancement of motivation for sucrose by a moderately high fat diet precedes metabolic derangements and overt obesity and suggests that behaviour may initially drive metabolic changes, rather than vice versa.”
They added that in this way, ingestion of high fat, and subsequent intake of sweet tasting high sugar foods could “jointly contribute to a metabolic profile that is high risk for both type2 diabetes and cardiovascular disease.”
“Our studies demonstrate increased motivation for sucrose in pubertal rats compared with adults, and this is enhanced by access to a moderately high fat diet,” concluded the researchers. “The effect of high fat diet upon sucrose motivation may be mediated by increased AGRP activity in the medial hypothalamus,” they added.
Published online ahead of print, doi: 10.1016/j.appet.2012.09.021
“Moderate high fat diet increases sucrose self-administration in young rats”
Authors: Dianne P. Figlewicz, Jennifer L. Jay, Molly A. Acheson, Irwin J. Magrisso, et al