Rats that were exposed to a 'junk food' diet in utero and as neonates before being weaned seem to prefer diets with higher levels of fat than do rats whose mothers ate standard rat chow, researchers recently reported. Further analysis suggests that exposure to this junk food diet is associated with altered development of the pathway regulating motivation and reward.

Clinical and experimental studies have shown that individuals exposed to high-fat, high-sugar diets before birth have increased risk of obesity later in life. Some research suggests that such 'maternal overnutrition' can predispose offspring to prefer high-fat, high-sugar foods. The mechanisms underlying food preference, however, remain unclear.

In this study, Beverly Muhlhauser and Z.Y. Ong of the University of Adelaide in Australia assigned female rats to one of two groups, each group consisting of six rats. The first group had free access to standard rat chow (FASEB J. doi:10.1096/fj.10-178392; published online 22 March 2011). The other rats had unlimited access to a junk food diet consisting of peanut butter, hazelnut spread, chocolate-flavored biscuits, extruded savory snacks, sweetened multi-grain cereal, ham- and chicken-flavored processed meat and a mixture of lard and standard rat chow.

The female rats ate their respective diets for four weeks before being mated up until they weaned their offspring. After weaning, the dam and one male and one female pup from each litter were killed. The remaining pups were given free access to standard chow and to a junk-food diet. A male pup and a female pup from each litter were killed at 6 weeks of age and another male pup and female pup from each litter were killed at 3 months. The research team carried out post-mortem analyses on rats.

Credit: Dario Egidi

The rats born to dams eating junk food were significantly lighter than control offspring; this difference persisted until weaning. Additionally, rats born to mothers exposed to the junk food diets had an increased preference for fat through at least 3 months of age. The altered expression of some genes in the rats with early exposure to a junk food diet was consistent with heightened activation of opioid and dopaminergic signaling within the central reward pathway, though this altered genetic expression was reversed by the time these mice reached 3 months of age. These results suggest a possible mechanism for how early life exposure to high-fat, high-sugar diets may lead to the development of childhood and adult obesity in humans.