Most of us wish we ate better. I know I certainly do. But when hunger strikes, and you’re standing in line at the grab-and-go food joint, that salad seems really lackluster sitting next to that tasty-looking cookie. I can’t help but think that my diet — and my waistline — would look a lot better if I just craved lettuce a little more.
Now a new study shows that although we may never cease to love cookies, we might be able to make that carrot a little more appealing. In overweight people, a behavioral intervention was associated with changes in how their brains responded to high- and low-calorie foods. The small pilot study is intriguing, but with just 13 participants, a larger study is needed before scientists will know if training the brain can make us abstain.
“Everyone responds more strongly to high-calorie foods than low-calorie foods. It’s just normal,” says study coauthor Susan Roberts, a behavioral nutrition scientist from Tufts University in Medford, Mass. While most people prefer brownies over beets, people who are overweight or obese have a harder time avoiding high-calorie foods, she says. “When someone becomes overweight, there’s a dampening effect on a number of brain structures, including the reward system,” she says. “It’s harder to enjoy food generally, and so when someone becomes overweight, they really want to eat those high-calorie foods, because those are the foods that activate reward systems to the biggest extent.”
Craving is a particular issue. Craving is distinct from hunger and focuses on a particular food, often foods that are high calorie. Other studies show that people who are obese have more cravings than those who are not. For the past few years, Roberts has been focused on developing a diet that targets cravings, rather than simply attacking weight. “Current programs are hard to stick with,” she says. “It’s all negative, it’s about weighing people or having enough willpower to put up with feeling unsatisfied. That is a major reason why people give up on them. Reducing cravings is one way to make it easier.”
Roberts and her colleagues came up with a behavioral intervention that combines recipes and menu plans, portion control and nutrition tips with group support sessions. A previous study from the group showed that over six months of group sessions and dieting, people did lose weight. As they did so, they also reported reduced food cravings.
The scientists wanted to know what effect this behavioral intervention might be having on the brain. They were particularly interested in reward related systems. In a study published September 1 in Nutrition and Diabetes, eight participants received the behavioral intervention (now marketed as the iDiet) for six months and had lost an average of 6.3 kilograms (13 pounds). A control group of five people was simply put on a wait list, received no behavioral training and gained an average of 2.1 kilograms (4.6 pounds) over six months.
At the beginning and end of the six-month intervention, Roberts and colleagues at Massachusetts General Hospital put each participant in an MRI scanner and showed them images of non-food items (a wallet or book), low-calorie food items (chicken or a healthy sandwich) and high-calorie food items (fries or mozzarella sticks). The participants were asked to rate how good they thought the food looked.
Meanwhile, the functional MRI scans detected blood oxygen levels in various parts of the brain. An increase in oxygenated blood flow to a region of the brain is thought to indicate more activity in that area. Compared with control participants, people who had been on the six-month diet showed more blood flow in the right ventral putamen when shown low-calorie food. With high-calorie food, the dieters showed a decrease in oxygenated blood flow in the left dorsal putamen compared to their wait-listed counterparts. The dieting group also rated high-calorie food as less palatable.
The putamen is a part of the brain’s striatum, an area associated with learning and reinforcement, wanting to perform a behavior again, or predicting that something is going to feel good. Roberts concluded that “it is possible to retrain your brain to like different food.” She says that the changes in blood flow indicate the six-month intervention changes the way people view the food they are faced with.
While the study holds promise for behavioral interventions targeting craving, it’s still not quite teaching your brain to love lettuce. The putamen did show more activity in response to low-calorie food, and a decrease in response to high-calorie food. But the low-calorie food was not seen as more palatable. We may grow to realize the perils of the steak, but that doesn’t make the salad taste any better.
Susan Carnell, an obesity researcher at Johns Hopkins University School of Medicine, says that while the brain changes are evident, it’s not clear what they mean for those on the diet. “What we don’t know is how important these striatal changes are,” she says. “They might just be one component in a much larger network of changes within the brain. They could also be the result of intervention-related changes in eating behavior and weight, rather than their cause.”
The study also raises many additional questions. No one knows if similar effects might exist in people of normal weight, or people who are severely obese. The study also could not address why the brain changes were there. Perhaps people who have been on an effective diet resist high-calorie foods more successfully. Maybe knowledge of what is a “bad” or a “good” food influences responses. Or maybe guilt over high-calorie foods plays into the results.
Carnell also notes that a study with only 13 participants has its limits. It could be that the eight participants in the intervention just happened to be different from the five controls. But she is impressed with the paper and hopes the study will be replicated with a larger group. “It’s a scientifically important study for our field,” she says. “It suggests that brain function is not ‘set’ and therefore overweight and obesity are not necessarily an individual’s ‘destiny’.”
Roberts agrees that “all nutrition science needs repeating, and that is definitely true here due to the small sample size.” She is also interested in other questions, including performing larger studies that compare her dietary intervention with others, and what other brain structures and food-related behaviors might be changed. “This is the first demonstration that these types of changes are possible,” she says. “Now we need a ton of studies to show all the brain areas that are affected.”