Can you 'think yourself thin'?

Today the Daily Mail reports that you can “think yourself thinner”. It says that researchers have found that “actively remembering your last meal suppresses appetite and reduces the desire to snack on junk food”. It also says the study found that concentrating on food while eating makes you less likely to get hungry later on.

These results are based on three experiments in healthy young people with a normal body mass index (BMI). It’s therefore not clear whether these results would apply to people who were underweight, overweight or obese. It’s also not clear whether this technique would be able to reduce snacking in the longer term, or to reduce a person’s overall calorie intake or weight.

Although thinking of a recent meal might help someone reduce their snacking, unless this is part of a programme that includes a healthy diet and increased physical activity, this technique seems unlikely to have much effect on weight loss.

Where did the story come from?

Dr Suzanne Higgs and colleagues from the School of Psychiatry at the University of Birmingham carried out the research. The study was funded by the Biotechnology and Biological Sciences Research Council. It was published in Physiology & Behavior, a peer-reviewed scientific journal.

What kind of scientific study was this?

In this experimental study, the researchers tested whether remembering a recent meal had an effect on snacking. They also wanted to see whether this effect varied depending on how appealing the snack was, how long ago the meal was eaten, and the person’s normal eating behaviour (specifically whether or not the person was usually restrained in what they ate).

The researchers carried out three experiments. All the participants answered a questionnaire about their lifestyles, including eating behaviour. This included 10 questions about dietary restraint (attempt to restrict food intake to control body weight) and 13 questions about disinhibition (tendency to overeat in certain situations).

The first experiment involved 14 healthy male students (average age of 21) with a normal BMI (19 to 25kg/m2). Afternoon test sessions were conducted on two different days and the participants were asked to eat their lunch at least two hours before the session. At the start of the first test session, they rated their appetites and mood at that time using a visual analogue scale (VAS). The VAS scale is a 10cm-long line; its opposite ends represent the extremes of the feeling being tested.

After this, the group was split into two. One group was asked to record in as much detail as possible what they ate for lunch that day, while the other was asked to write down what they had for lunch the day before. After this, the participants again gave their appetite and mood ratings.

All the participants were presented with three bowls of popcorn with differing levels of salt (high, low, and no salt). They were then asked to rate how tasty, sweet, salty, and sour each bowl of popcorn was using a VAS scale ranging from ‘not at all’ to ‘extremely’. They were also asked the likelihood that they would choose to eat from each bowl again. The participants were told to eat as much of the popcorn as they needed to rate its taste, and that after rating the popcorn they could eat as much of it as they liked. After the experiment was finished, the bowls of popcorn were weighed to see how much had been eaten.

On the second test day the groups switched tasks. The researchers analysed how much popcorn was eaten, taking into account what the volunteer was told to recall, how salty the popcorn was, and the order in which they were tested (i.e. whether they had to recall that day’s or the previous day’s lunch).

The second experiment involved 73 healthy female students (average age of 20). Using the questionnaire, the participants were given scores of their eating restraint and disinhibition and people with different combinations of these characteristics were randomly assigned to recall that day’s lunch or that of the day before. They also all had an introductory day where there was no recall, and they tasted and rated the popcorn. After this, the procedure remained similar to the first experiment, but the groups were not switched. The researchers then compared the effects of different eating restraint and disinhibition scores to the results.

In the third experiment, 47 healthy female students (average age of 22) were given a standardised lunch containing 400 calories. They then completed the snack experiment, this time with three types of cookies rather than popcorn. The experiment was carried out on two days, the first occasion one hour after lunch, and the second three hours after lunch. Half of these participants were asked to recall their lunch, while the other half were asked to recall their journey to the test centre.

What were the results of the study?

In the first experiment the researchers found there was no difference in appetite ratings either before or after recall, between people recalling either that day’s or the previous day’s lunch. Despite this, when people recalled that day’s lunch they ate less popcorn than when they recalled the previous day’s lunch.

Overall, people ate more salted popcorn than non-salted popcorn, and this was not affected by what meal a person had recalled. The more salt the popcorn had, the more pleasant people thought it tasted, and again this was not significantly affected by what meal a person had recalled.

In the second experiment they found that a person’s normal eating restraint did not affect how much they ate, but that only people who had low disinhibition scores (i.e. did not have a tendency to overeat) reduced their intake after recalling today’s lunch.

What interpretations did the researchers draw from these results?

The researchers concluded that recalling that day’s lunch reduced consumption of both low and high calorie snacks (popcorn or cookies). This was not related to how pleasant the snack tasted, and seemed to be greatest in people who did not have a tendency to overeat, and appeared to depend on memory, as there was a delay before recall had an effect.

What does the NHS Knowledge Service make of this study?

This was a small study that looked at the effect of recent meal recall on snacking. There are a number of limitations to consider:

• All of the participants were healthy young people, with BMIs in the normal range. It’s not clear whether the same effect would be seen in older people or children, people who were less healthy, or people outside of the normal BMI range.
• This study only looked at the effects of meal recall on snacking in the short term. It’s not clear whether this technique could reduce snacking if used on a regular basis, or whether the reductions in snacking seen would have any effect on a person’s overall calorie intake or weight.

Reducing weight is difficult for some people, and thinking of a recent meal might help them reduce their snacking. However, unless this is part of a programme that includes a healthy diet and increased physical activity, this technique seems unlikely to have much effect.

Sir Muir Gray adds…

Though not conclusive, this study recommends an intervention that can do no harm and costs nothing. So even though it’s just a single study, it’s worth giving it a go – good remembering.