Niha Zubair, Arivale Clinical Research Scientist, PhD
There’s a biological reason that double-bacon cheeseburger with large fries and, why not, a milkshake to wash it down sounds so good.
Our desire for foods is regulated by processes within our bodies. The foods we desire most are those typically of higher caloric value, which are usually foods high in fats or carbohydrates. We desire fats and carbs because eating them activates our brain’s reward system by increasing the neurotransmitter dopamine, or the “happy hormone.”
But how do our brains react to foods that are high in both fats and carbs – which happen to be many of the processed foods available today?
A group of scientists sought to answer that question in a study published this month in Cell Metabolism and covered by Scientific American. The scientists hypothesized that the simultaneous activation of both the fat and carbohydrate gut-brain pathways – fats and carbs have different gut-brain pathways, but both lead to a rewarding dopamine release – would produce a physiologic response that would render foods high in both these nutrients more rewarding, calorie for calorie, than foods high in only fats or only carbs.
Understanding what high-fat, high-carb foods do to our brains is particularly important given the ongoing obesity epidemic. Foods high in both fats and carbs are prolific in the modern food environment but were quite rare in our ancestors’ diet, which was mostly composed of plants and animal meat. Furthermore, these ancestors were hunter-gatherers, so they rarely ate multiple types of foods at a time. Even if high-fat, high-carb foods were eaten together, they were full of fiber, which slowed the rate of carbohydrate metabolism.
In this new study, 206 adults underwent brain scans while being shown photos of familiar snacks containing either mostly fat, mostly carbs, or a combination of both fat and carbs. In addition, participants were given a limited amount of money to bid on their first-choice food. Lastly, participants were asked to estimate the calories in the various foods.
Both the brain scans and bidding experiment found that foods high in both fat and carbs were seen as more rewarding, calorie for calorie, than foods high in only fat or only carbs. In fact, scientists found this reward was higher than if you added the reward from the fat and the reward from the carb individually (what they called a “supra-additive” effect). For example, given the choice between cheese (fat), gummy bears (carbs), or ice cream (fat and carbs), all of equal calorie amounts, the ice cream was viewed as more rewarding than the cheese and gummy bears combined.
In addition, the scientists found that participants were better able to estimate the calorie content of foods high in fat, while they were unable to do so for foods high in carbs or foods containing both fat and carbs.
Overall, the scientists concluded that combining fat and carbs increases the reward value of foods, independent of calorie content, and disrupts our ability to accurately estimate the calorie content of sweet-fatty foods.
In addition, they suggest these results may represent one way by which our current food environment rich in processed foods leads to overeating and thus obesity.
It’s not earth-shattering news that foods high in both fat and carbohydrates, like most processed foods, are desirable, but this study reinforces that sticking to foods in their whole, unprocessed form may prevent overeating. And, eating an unprocessed diet rich in plants, fiber-rich carbs, and healthy fats also has other health benefits, such as improved heart-health and cancer prevention.
If avoiding processed foods is difficult because of cravings, cognitive-behavioral strategies like removing these foods from your environment – or at least putting them out of sight – or focusing your thoughts on your health goals and core values may help you resist the temptation.
One limitation of this study is that the scientists didn’t measure the frequency of consumption of each of the foods surveyed. For example, it’s possible that those who frequently consume ice cream could have a blunted reward response to that food compared to someone who rarely consumes it.
Another limitation is that the food items used were only those common to western Europe (the study took place in Germany). Future studies should expand the food items to represent the diet of other regions of the world.
Neither of these limitations was mentioned in the Scientific American coverage of the study.