This should be of particular concern, given recent evidence that the path between memory and obesity may go both ways, as attention and memory control our appetite and eating behaviour. In other words, a deficit in your memory could cause you to gain weight.
Early evidence that memory plays an important role in eating behaviour came from a 1998 study showing that patients with severe amnesia will readily eat multiple meals one after the other, because they could not remember that they had just eaten.
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“This shows that when we’re deciding how much to eat we’re not just basing those decisions on physiological signals about how much food there is in our stomach, but also on cognitive processes like memory,” says experimental psychologist Eric Robinson of the University of Liverpool.
“If your memory’s impaired or just not very good then you might overeat,” he adds. “I wanted to know if this could be reversed. If you improve a person’s memory, could that be a useful way of getting them to eat less?”
Robinson and his colleagues recruited 48 overweight or obese people and invited them to eat lunch in the lab. The participants were randomly divided into two groups, and given audio recordings to listen to while they ate.
Those in one group listened to audio instructing them to pay attention to their food, while those in the other listened to an audio book with non-food related content.
The researchers then invited them back the following day, presented with some high-energy snacks, and measured how much they ate. They found that those who had been instructed to focus on their lunchtime meal the previous day ate nearly one third less of the snacks than those who had been distracted by the audio book.
A larger follow-up study confirmed these findings. This time, Robinson and his colleagues randomly assigned a total of 114 women to one of two groups, and tried to manipulate the extent to which they were aware of their eating behaviour.
Again, they gave all participants the same lunchtime meal, consisting of a ham sandwich, mini sausage rolls, a packet of crisps, rice cakes, chocolate chip cookies and seedless grapes.
Before sitting down to eat, the participants in one group were told that they were taking part in a study of eating behaviour, and that the amount of food they ate would be measured. The rest were told that they were taking part in a study of how their thought processes and moods change during the course of the day.
The researchers found no overall difference between how much participants in both groups ate. Those who had been told that they were taking part in a study of eating behaviour tended to eat fewer cookies than those in the other group, however, apparently because their awareness of their own food consumption was heightened.
Attention and memory are independent of each other, but they are closely linked – we cannot remember something that we did not pay attention to and, by the same token, our memories of something tend to be more vivid the more we attend to it.
It’s therefore possible that a vivid memory of lunch could reactivate the body’s physiological state, so that we do not feel so hungry, and consequently eat less at dinner. On the other hand, someone who was distracted during lunch would form weak memories of the meal, and so thinking about it at dinner might make them feel hungrier and eat more.
In one 2011 study, for instance, half the participants played Solitaire on a computer while eating their lunch. Sure enough, they had hazier memories of their lunch and went on to eat significantly more biscuits later on than those who did not.
This is particularly interesting, given the evidence that over-eating can impair your memory, with both the over-eating and the memory problems reinforcing each other, pushing you down a slippery slope. “Our research suggests that you might eat more if you have an impaired memory,” says Robinson, “so you end up in a vicious cycle where memory’s impaired by an unhealthy lifestyle, and then that impairment promotes over-consumption.”
He points out that we still have to be careful not to draw firm conclusions, though, until we have stronger proof that this vicious cycle exists and has a real effect on people’s health. “This idea makes sense intuitively, but there’s still no direct evidence for it.”
STAGING AN INTERVENTION
In the meantime, the finding that food memories and awareness can influence eating behaviour does at least suggest a novel way of helping people lose weight and maintain a healthy BMI, and Robinson and his colleagues have developed a smartphone app that encourages people to eat more attentively.
“There’s now convincing evidence that attention and memory affect how much people eat, but this comes from laboratory studies,” says Robinson.“We’re trying to see if the lab findings translate to the real world. Our app encourages people to take photos of what they’re eating and answer questions about their meals, the idea being that creating vivid memories will make them less likely to overeat during the day.”
Cheke and her colleagues are now following up their initial findings by trying to pick apart the various factors that contribute to obesity, in order to try to determine which are likely to influence brain structure and function.
They are also using a smartphone app to collect information about people’s lifestyles and behaviour, and are recruiting volunteers in and around Cambridge to help them gather the data they need.
“One person may be obese because they don’t do any exercise and eat a lot of junk food,” says Cheke. “Another might be obese for genetic reasons but actually eat really well and do lots of exercise, and yet another may be obese because they have insulin problems.”
“We’re trying to get all these different variables to see the relative contribution, so we’ve got people out wearing activity monitors and filling food diaries for us. Doing studies like this is the only way we’ll be able to tease these things apart.”