It's been hard to find time for Food Reward Friday lately, but this week I'm bringing it back with a vengeance. Oreos have been one of America's favorite cookies since their introduction in 1912 by Nabisco. They boast a tempting combination of crunchy chocolate cookie and soft, sweet filling. From a food reward perspective, the combination of concentrated sugar, starch and fat make them a winner. From a nutritional perspective, these same factors make them a loser.
Although most adults can think of other desserts we'd rather eat, I think many of us can remember a time when Oreos were just about the pinnacle of deliciousness. More than tasty enough to throw a tantrum for. It also helps that Oreos lend themselves to playing with your food.
Interestingly, Oreos were the subject of a recent study on food reward in rats (1) that WHS reader Chris Cappuccio passed on to me. This study, presented at the 2013 Neuroscience conference, got a lot of media attention, both positive and negative. What did it find?
Food reward is the process by which behaviors are reinforced by food, and a "rewarding" food is one that makes you more motivated to obtain it once you've eaten it a few times. In the current study, researchers used a measure of reward called conditioned place preference. Basically, they repeatedly gave rats Oreos in a particular location, and then measured how much time the rats subsequently spent hanging around in that location hoping for Oreos*, even when the Oreos were omitted. Crucially, the Oreos were pitted against healthy bland rodent chow, not against an absence of food.
They found exactly what has been shown many times before: rats LOVE human junk food. The rats trained with Oreos preferred to hang around the Oreo-associated location even when no Oreos were there, demonstrating that the Oreos are highly rewarding (i.e. Oreo consumption increased the likelihood of Oreo-seeking behavior). Oreos are also highly rewarding in humans, otherwise they would not have sustained human Oreo-purchasing behaviors over the last century.
What comes next is the experiment that made this study so controversial: they compared the reward value of Oreos to the reward value of cocaine and heroin in their experimental model. Intravenous cocaine or heroin was paired with a specific location, pitted against intravenous saline at another location, and the researchers subsequently measured how much time the rats spent hanging around the side paired with drug even when no drug was administered.
As expected, rats like cocaine and heroin, and they spent more time hanging around the drug-associated location hoping for a hit. Here's the critical finding: in this experiment, the reward value of heroin and cocaine was not significantly different from the reward value of Oreos. Also, all three conditions caused similar effects on neuron activity in the key reward-related brain region the nucleus accumbens. The authors end the abstract with this:
These findings suggest that high fat/sugar foods and drugs of abuse trigger brain addictive processes to the same degree and lend support to the hypothesis that maladaptive eating behaviors contributing to obesity can be compared to drug addictionThis is what triggered the avalanche of positive and negative media coverage. The negative coverage was mostly from people who are tired of hearing the argument that reward and addiction are the same thing, or that activation of brain regions involved in reward means something is addictive. These people have a point, but there's a baby in the bathwater that we shouldn't discard.
Drug addiction is basically a very strong motivation to obtain the drug, as a result of the drug's high reward value (due to direct actions on brain reward circuits). A person is so motivated to obtain a drug that she has a hard time controlling drug-seeking and drug use behaviors, and these behaviors supersede constructive behaviors like maintaining relationships and being financially responsible.
Similarly, people can be highly motivated to obtain certain foods (ice cream, pizza, potato chips, Oreos) due to the high reward value of those foods. Although calling this 'addiction' is controversial, it does lead to the consumption of unhealthy calories in excess, superseding constructive behaviors like eating an appropriate quantity of healthy food.
The word 'addiction' triggers strong emotional reactions and quickly leads to unproductive debate in the popular media. I think the best way to think about this study is to discard the word 'addiction' and simply think about reward. Oreos, cocaine, and heroin all had a powerful ability to motivate behavior in rats. Even though we can't do this study in humans, and I doubt humans would find Oreos as rewarding as heroin, it is nevertheless clear that Oreos and other similar foods are highly rewarding in humans and can lead to behaviors that undermine health and other positive life outcomes. This study is a good reminder of that.
* In a manner of speaking. We can't read their minds to see if it truly contains hope. See comments below by Aaron Blaisdell.