Doughnuts or Broccoli?: Why Dieters Fail and How to Succeed

Brain research explains why we choose tasty unhealthy snacks over healthy foods.

Posted Jul 17, 2019

The prevalence of obesity among U.S. adults and children is alarming, particularly because obesity increases the risk for debilitating diseases. According to the CDC, the prevalence among adults was 39.8%, 20.6% in adolescents, and 18.4% in school-aged children. Paradoxically, the U.S. weight loss market is worth $66 billion. Something does not add up. Why is it so hard to eat healthy? Why is relapse to our old unhealthy diets the norm and not the exception? Just like other choices in life, choosing a doughnut over broccoli has to do with how the brain generally makes decisions. Certainly, self-control is imperative for healthy eating and for general optimal decision making.

Two brain areas are relevant to goal-directed decisions and cognitive control, the ventromedial prefrontal cortex (vmPFC) and the dorsolateral prefrontal cortex (DLPFC), respectively. These regions seem to be involved when we choose between an alternative with higher value and a more tempting but inferior option, such as between fruit and your favorite ice cream. Dr. Hare and colleagues at the California Institute of Technology in Pasadena studied a group of dieters to examine the neuroscience of such choices. Participants had to make real decisions about what foods to eat while in a functional neuroimaging scanner (fMRI).

There were three phases: In the first two phases, dieters rated 50 different foods for taste and health separately. In the third phase, the subjects were asked to choose between foods and items that they had rated as neutral in both health and taste. They also rated how confident they were in their decision (strong no, no, neutral, yes, or strong yes). Of course, dieters should be concerned with the healthiness of the food and not just taste. Then, the participants were classified as self-controllers (SC) or non-self-controllers (NSC) on the basis of their food choices. As expected, SCs made food choices based on both healthiness and taste and rejecting most liked but unhealthy foods. NSCs made decisions on the basis of taste alone.

The results suggest that vmPFC computes the value of the food choice regardless of whether it is a doughnut or a vegetable. But this region does not have the final say. So, you might know that the doughnut will taste better than broccoli, but you still select broccoli. Another nearby region supervises the vmPFC. The DLPFC plays a crucial role in the self-control necessary for selecting the less tasty but healthier food option. In this study, activity in DLPFC increased when participants selected healthy as opposed to unhealthy and tasty. There were differences in the brains of SC and NSC groups in trials in which liked-but-unhealthy foods were avoided. The more the vmPFC placed a high value on the tasty food, the less activation in the DLPFC, leading to successfully rejecting the unhealthy tempting food.

The question we are all thinking is how can we have brains like the self-control group? How can we foster healthy connections between vmPFC (this will taste so yummy) and DLPFC (this is unhealthy)? We need more research on individuals who exercise high control in societies where unhealthy tasty food is available in abundance and cheap. What can you do now? DLPFC is implicated in general intelligence, cognitive control, and emotional regulation. Thus, it is not surprising that activity in this region would also be associated with better food choices. So anything you do to increase your general intelligence and emotional regulation should also impact better food choices. These skills would also endow you with more self-control in situations where you have to make a choice between a tempting unhealthy and a less tasty healthy option. This is applicable beyond food choices: drug addiction, saving vs. spending, bullying vs. siding with the victim . . . the applications are endless.