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Researchers at the University of Adelaide, expanding upon previous work, have found that there are two critical time periods in a person’s life where exposure to junk food creates the disposition to overeat foods high in fat and sugar. These most harmful periods occur during the later stages of pregnancy, as well as adolescence, and have particularly damaging repercussions for females, Medical Daily reports.

In April of 2013, researchers conducted their first tests of how a junk food diet affects children still in the womb under Dr. Bev Muhlhausler, senior research fellow in the University’s FOODplus Research Centre. Published in FASEB Journal, the study concluded that junk food consumed by the mother during pregnancy and lactation desensitized offspring to the normal reward system resulting from these types of foods.

Typically, the body produces opioids, a chemical that triggers a reward response, when we consume fat and sugar. These opioids initiate the production of dopamine, the “feel good” hormone that results in the often euphoric enjoyment we derive from these types of foods. However, with increased exposure to sugar and fat, the body needs a higher intake of unhealthy foods in order to produce the same good feeling.

“We found that the opioid signaling pathway (the reward pathway) in these offspring was less sensitive than those whose mothers were eating a standard diet,” Muhlhausler said. As a result, children of mothers who have consumed a high-fat, high-sugar diet while pregnant crave more sugar and fat than those who chose healthier options, predisposing them to overeating.

Muhlhausler equates this response to a type of addiction. “In the same way that someone addicted to opioid drugs has to consume more of the drug over time to achieve the same ‘high,’ continually producing excess opioids by eating too much junk food results in the need to consume more foods full of fat and sugar to get the same pleasurable sensation,” she said.

Now, researchers have discovered that particular times within pregnancy, as well as early stages of adult development have more of an effect on this desensitization. “Our research suggests that too much junk food consumed late in pregnancy for humans has the potential to be more harmful to the child than excess junk food early in the pregnancy,” said Dr. Jessica Gugusheff, post-doctoral researcher in the School of Agriculture, Food and Wine. Similarly, Gugusheff also found that if a mother consumes large amounts of junk food during early stages of pregnancy, there is potential to reduce negative effects if a healthier diet is adopted later on during pregnancy.

“The second critical window is in adolescence and we’ve found differences between males and females,” Gugusheff said. “Our experiments showed that eating a healthy diet during adolescence could reverse the junk-food preferences in males, but not females.” Males have more of a chance to combat cravings created within the womb, while females do not have as great of a chance if their mother had a sweet tooth while pregnant.

“The brain area grows at its fastest during these critical windows and is therefore most susceptible to alteration at these times,” Muhlhausler said. She and her team hope that their research will allow pregnant women to make more informed decisions about their diets, knowing the effects it will produce on their children later on in life. Muhlhausler also concluded, “It will also enable us to target dietary interventions to times in development when they will be most beneficial.”