A huge sundae with cookies turning up on the big screen, the smell of fries or the sight of a greasy-juicy burger: cues for food, smells and images in particular, often tempt us to spontaneously buy these foods – even if we do not feel hungry or know that doing so does our health no good.
Yet with respect to high-calorie foods even mere words lead effectively enough to the same outcome. This is especially problematic for the growing number of overweight and obese people – and for patients with eating disorders such as binge-eating disorder. It is especially important with these people to develop counter-strategies to withstand the “temptations” delivered by advertising, and to be able to resist these ubiquitous fat-harbouring offers.
“Chicken wings” – barely read, already down the hatchet?
The influence of such words has now been studied by a research team led by Susan Carnell from the Global Obesity Prevention Center at Johns Hopkins University in Baltimore (USA). The researchers presented their findings in November at the “Obesity Week” event in Los Angeles.
In their first study Carnell and her team showed words denoting high and low kilojoule foods to 12 lean and 17 obese subjects and examined the brain activity using functional magnetic resonance imaging (fMRI). At the same time, the participants were asked to indicate how much they wanted to eat the respective foods. Following this various foods were offered to them, which they were permitted to eat freely.
Obese participants showed a stronger brain response to words representing high-kilojoule foods –such as “chicken wings” or “chocolate spread” – than did lean subjects. Regions more strongly activated were among others the dorsolateral prefrontal cortex (DLPFC) and the gyrus cinguli regions – regions which have to do with the processing of emotions and control of impulses. If the participants had under experimental conditions experienced social stress, both groups responded to the “sweet and greasy” words with stronger activations in the brain. Nonetheless, only obese subjects took in more kilojoules following this than if they had experienced no stress.
“The brain’s enhanced response to food stimuli – both under stress as well as in a stress-free state – could explain how increased food intake and weight gain occur”, write the researchers. Knowledge of such activation pattern could help in developing new medications or in evaluating the success of therapies.
All a question of genes?
As part of a second study done by the same authors, 35 teenagers aged 14 to 19 took part. A relationship between the reaction to the food words and the genetically defined risk for obesity was able to be observed here – one defined by the number of risk alleles for all four gene variants being investigated. Subjects with an increased obesity risk felt a stronger sense of desire after viewing the food words. In addition, a specific gene variant (FTO) was associated with a lower sense of self-control when eating. Moreover subjects with a risk allele for another gene variant (MC4R) tended to eat more kilojoule-rich food after seeing the word.
“The results suggest that genetic risk factors for obesity affect body weight through varied mechanisms”, the researchers write. One of these factors was an increased desire for food, which can be triggered by words, images or smells of food. Overall, the studies suggest that stress and environmental influences – such as advertising of certain foods – alter brain activity and so may affect eating behaviour. “That makes it difficult for some people to regulate their food intake appropriately – especially for people with obesity or a genetically increased risk for it”, explains Carnell.
Torn by internal conflicts
With eating disorders as well, the brain seems to respond differently to food stimuli. Here patients with a binge eating-disorder suffer from binge eating, whereby large volumes of food are gobbled down in an uncontrolled manner. In a study [Paywall] at the Mount Sinai School of Medicine in New York and the Johns Hopkins University, 10 women with and 10 women without binge eating-disorders observed photos of high and low-kilojoule foods or heard the terms describing them. At the same time their brain activity and the connection strength between different brain regions (functional connectivity) were measured. Women with binge-eating disorder showed increased activity in the anterior cingulate cortex in association with high-calorie foods – and stronger links between this region and other regions of the brain such as the insular lobe and the cerebellum. This suggests that those affected experience internal conflicts at the sight of food – for example conflict between the desire to eat and the desire to control their eating. Naturally, further studies are needed to verify the results.
Paths towards stronger self-control
These and similar studies could however also highlight ways in which the individuals concerned can better resist the temptations of their environment. Thus a study [Paywall] by researchers at the University of Cape Town (South Africa) revealed that the overweight can learn to better control their impulses. The scientists led by David John Hume studied 51 overweight or obese women who had either taken off their weight successfully, were still overweight or had after such dieting returned to their original weight. The subjects viewed pictures of food, while their brain activity was measured using EEG.
Women who had successfully reduced their weight showed more signs of control in their brain activity at the sight of food images. At the same time they were less likely to eat from desire alone. Such results could help in understanding how someone could achieve more control over the ever-present food stimuli, the authors write. “This could help in developing new therapeutic approaches that can contribute to long-term weight loss”, says Hume.
Learning how to resist those sweet temptations
Susan Carnell is convinced that both the reactions of the brain and eating behaviour are definitely changeable. “Therefore, people with obesity or elevated risk of it ought not give up hope – they are not doomed to remain fat or to become so,” says the psychologist.
One possibility is, for example, to modify the immediate environment, to reduce the risk of unduly taking in many kilojoules. “Instead of looking at a menu in a restaurant, the persons concerned could ask the waiter to indicate to them only the healthiest meals”, says Carnell, “And those places where many high-kilojoule dishes are offered should rather be avoided – such as fast-food restaurants or canteens”.
Whoever tends to overeat, especially under psychological tension, can learn strategies to reduce stress or to cope better with it. At the same time the person concerned can practice timely recognition of a “stress eating” event, and put in action targeted countermeasures – for example, by talking to a friend instead, meditating or taking a walk.