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Think Healthy, Eat Healthy?
7/28/2011
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You’re trying to decide what to eat … salmon and spinach, or a burger and fries.
 
As it turns out, making that choice is a complex process involving different parts of the brain, with distinct functions.
 
And, according to research from the California Institute of Technology (Caltech), food decisions can be influenced by focusing your attention on health.
 
This discovery may help us all make healthier choices not just in terms of food, but in other areas, like whether or not we drive or bike to the store.
 
Practically speaking, it suggests that food packages and restaurant menus that label a choice “healthy” may have more impact than supposed.
 
In turn, this seems to make it even more important than presumed for government to define “healthy” carefully and bar misuse of the term.
 
The devil and angel in your brain
Findings reported from Caltech suggest that when you decide what to eat, your brain considers several factors almost instantaneously.
 
These factors include each food’s perceived taste appeal, health benefits, size, and appearance … and your perceived value of each of those attributes relative to the others.
 
Two years ago, Professors Antonio Rangel of Caltech and Todd Hare of the University of Zurich published a paper describing differences in the brains of people who are good at exercising self-control.
 
They found that everyone uses the same area of the brain – the ventral medial prefrontal cortex, or vmPFC – to make value-laden decisions like what to munch on.
 
But they discovered that a second brain area – the dorsolateral prefrontal cortex or dlPFC – “lights up” when a person is exercising self-control during the decision-making process.
 
When the dlPFC is active during a food-choosing decision, it forces the vmPFC to weigh a food’s perceived health benefits as well its taste and other attributes.
 
And the new study reveals that “external cues” can help kick-start the dlPFC and thereby encourage more self-control.
 
A little forethought can affect food choices
The researchers conducted a brain-imaging experiment with 33 adult volunteers, none of whom were following a specific diet or trying to lose weight for any reason.
 
Each of the volunteers was shown 180 different food items—from chips and candy bars to apples and broccoli—through a set of video goggles while in a functional magnetic resonance imaging (fMRI) machine.
 
The subjects were hungry, having been asked to fast for at least three hours prior to the experiment, and were given up to three seconds to respond to each picture with a decision about whether or not they'd want to eat the food shown after the experiment was over.
 
They could either give the food a “strong no”, a “no”, a “yes”, or a “strong yes” to the idea of eating the food.
 
Once all of the images had been flipped through, a single food image was chosen at random; if the volunteer had said “yes”, or a “strong yes” to that food, he or she was served that item.
 
However, before every 10 food choices, an instruction would come on the screen for five seconds telling the subjects either to “consider the healthiness”, “consider the tastiness”, or “make decisions naturally”.
 
This meant that of the 180 decisions, the subjects made 60 in each of the three “instruction conditions.”
 
The point of the instructions was to shift the subject’s attention during the experiment and potentially influence their decisions.
 
Afterward – outside the fMRI scanner – the subjects were asked to rate the same foods on both a tastiness scale (very un-tasty, un-tasty, tasty, very tasty) and a healthiness scale (very unhealthy, unhealthy, healthy, very healthy).
 
Accordingly, the researchers were able to associate the choices the subjects made during the brain scan with their stated perceptions of those foods’ taste and health attributes.
 
This post-scan rating might show, for example, that a subject who chose broccoli during the “consider the healthiness” portion of the test might rate it as un-tasty after leaving the scanner.
 
The researchers then classified the foods for each subject based on that subject's ratings: unhealthy/un-tasty, healthy/un-tasty, unhealthy/tasty, and healthy/tasty.
 
Unsurprisingly, people chose healthy/tasty foods no matter where their attention had been directed.
 
But things got interesting when the researchers looked at the other three categories:
  • When thinking about healthiness, subjects were less likely to eat unhealthy foods, whether or not they considered them tasty.
  • When thinking about healthiness, subjects were more likely to eat healthy/un-tasty foods.
  • Being asked to think about healthiness led subjects to say “no” to foods more often than they did when asked to make decisions naturally.
Unsurprisingly, there were no significant differences between the choices made during the “consider the tastiness” and “make decisions naturally” portions of the experiment.
 
When the researchers turned to the fMRI results, they found that the vmPFC was, as predicted, “more responsive to the healthiness of food in the presence of health cues,” says Dr. Rangel.
 
And, as they’d seen previously, the robustness of that response was due to the influence of the dlPFC … the brain’s bastion of self-control.
 
Compared with when they were asked to consider healthiness, the volunteers’ dlPFC self-control centers were much quieter when the subjects were thinking about taste or their “natural” choice.
 
As Dr. Hare said, “This increased influence of the health signals on the vmPFC results in an overall value for the food that is based more on its health properties than is the case when the subject's attention is not focused on healthiness.”
 
And as Hare noted, “Our findings are also relevant to the current changes to cigarette warnings many governments have started to make. These changes include adding graphic images of the health risks of smoking. It remains to be seen whether these images will be more effective in drawing attention to the unhealthiness of smoking than the text warnings. If the graphical warnings do increase attention to health, then our results suggest that they could decrease the desire to smoke.”
 
Based on the Caltech team’s findings, it seems that focusing attention on the health aspects of foods changes value signals in the vmPFC and improves eating choices.
 
The study was funded by a grant from the National Science Foundation.
 
 
Sources
  • Hare TA, Malmaud J, Rangel A. Focusing Attention on the Health Aspects of Foods Changes Value Signals in vmPFC and Improves Dietary Choice. J Neurosci, 27 July 2011, 31(30):11077-11087; doi:10.1523/JNEUROSCI.6383-10.2011
  • Krajbich I, Armel C, Rangel A. Visual fixations and the computation and comparison of value in simple choice. Nat Neurosci. 2010 Oct;13(10):1292-8. Epub 2010 Sep 12.
  • Plassmann H, O'Doherty JP, Rangel A. Appetitive and aversive goal values are encoded in the medial orbitofrontal cortex at the time of decision making. J Neurosci. 2010 Aug 11;30(32):10799-808.
  • Williams-Hedges D. Think healthy, eat healthy: Scientists show link between attention, self-control. California Institute of Technology (Caltech), July 27, 2011. Accessed at http://media.caltech.edu/press_releases/13439
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