Tuesday May 7 2013
Being hungry is known to affect people's judgement about food
"Hungry shoppers 'buy more calories'," BBC News reports in a story based on a very small short-term study. The somewhat artificial study examined the effects of people skipping meals due to everything from busy lifestyles to intermittent diets such as the 5:2 diet.
These intentional or unintentional fasts may lead to unhealthy food choices being made at the shops. This research looked at whether being deprived of food for just a few hours has an effect on the types of food people opt for.
During a simulated shopping experience, the researchers found that people who were hungry selected more high-calorie foods than people who had just eaten a snack.
Similarly, people who went food shopping during times of the day when the researchers expected them to be hungry (late afternoon) purchased more high-calorie foods than people who shopped when the researchers thought they were less likely to be hungry (early afternoon).
However, no definitive conclusions can be drawn from these findings. The research had many limitations, including the fact that the first study was laboratory-based and laboratory findings may not reflect the real world.
But it is common sense to grab a bite to eat before heading to the shops, and might be worth a try if you do find that shopping when hungry means you make less healthy food choices.
Where did the story come from?
The study was carried out by researchers from Cornell University in the US and was funded by the university. It was published in the peer-reviewed Journal of the American Medical Association (JAMA) Internal Medicine.
The BBC covered the study well, if slightly uncritically, as the study's limitations were not discussed.
What kind of research was this?
This research included two components (a laboratory study and a field study) designed to determine whether short-term food deprivation changes affect food shopping habits.
The researchers say that food deprivation has been shown to change how much food people buy, and fasting is known to alter how the brain reacts to certain foods. They were interested to know whether shopping while hungry also effects the types of food people purchase.
Laboratory and field studies can provide interesting information about how people may react in given situations, but they are prone to bias and confounding. These potential limitations should be kept in mind when considering the results of the study.
What did the research involve?
In the first part of the study, the researchers recruited 68 paid participants with ages ranging from 18 to 62 years. They were asked to avoid eating for five hours prior to the start of the experiment.
The participants were grouped together in sessions of six to 12 people. In half of these sessions, a plate of crackers was offered at the beginning of the experiment and participants were asked to eat enough of the crackers so that they were not hungry. The participants were not offered any food in the remaining sessions.
The groups then completed an experiment meant to simulate buying groceries online. The online store offered a mix of lower calorie foods (including fruits, vegetables and chicken breasts) and higher calorie foods (including sweets, salty snacks and red meat). The products were displayed without prices. The researchers recorded and compared the food choices of individuals who did not eat prior to the study with those who had been offered a snack.
The second study involved the observation of individuals in a more natural setting. The researchers tracked the food purchases of 82 people.
The first group were tracked during the early afternoon, or "low hunger hours" (between 13:00 and 16:00), when the researchers expected them to have had lunch and therefore not be hungry.
The second group was tracked during the early evening, or "high hunger hours" (16:00 to 19:00), when researchers thought they would have gone several hours without a meal.
The researchers characterised the food purchases as either high-calorie or low-calorie, and compared the number of foods that fell into each category between the two participant groups.
They statistically compared the number of low-calorie items, the number of high-calorie items, and the ratio of low- to high-calorie purchases between the groups.
What were the basic results?
The researchers found that participants in the hungry and not-hungry groups of the laboratory study chose a similar number of total items (approximately 14 in the hungry group versus 12 in the not-hungry group).
The two groups also chose similar numbers of low-calorie foods (approximately eight in both groups), but the hungry group selected significantly more high-calorie items (an average of nearly six, compared with four in the not-hungry group).
During the field study, the researchers found that participants in the evening group purchased fewer low-calorie items (approximately eight items) than the afternoon group (approximate average of 11 items). There was no statistical difference in the number of high-calorie foods purchased (approximately four in both groups).
The ratio of low- to high-calorie items (with a higher ratio indicating better food choices overall) was significantly higher in the early afternoon group (approximately four low-calorie items per each high calorie item) compared with the evening group (approximately 2.5 low-calorie items per each high-calorie choice).
How did the researchers interpret the results?
The researchers concluded that, "even short-term fasts can lead people to make more unhealthy food choices" by picking fewer low-calorie foods.
This study suggests that how hungry you are when you shop for food can have an impact on the food you choose.
This may not be too surprising for anyone who has made a quick trip to the shops while hungry and found themselves at the till with a basket full of crisps and biscuits, but no fruit or vegetables.
While interesting, the study has some limitations that should be noted:
- Both experiments were fairly small, with less than 100 people in each.
- A laboratory-based study such as the first experiment tends to be stronger the more it mimics the real world. A simulated online grocery shopping experience that removes item price as a contributing factor is less likely to mirror real-life decision making.
- The field study makes assumptions about hunger levels based on the time of day. This may not be a reliable manner in which to assess hunger – for instance, individuals shopping during the "low hunger hours" of 13:00 to 16:00 may have skipped lunch, while individuals in the "high hunger hours" may have had a late lunch, a snack, or an early dinner.
- Field studies are prone to confounding due to difficulties measuring and controlling for different factors that may also have an influence. It is not reported how the afternoon and evening shoppers differed, and it is possible that the relationship between the time of day and shopping choices was influenced by different participant characteristics, such as age, employment, education, or socioeconomic status, and not by hunger.
The researchers say that short-term fasting is fairly common and can arise from skipping a meal, either intentionally as part of a religious fast or in an effort to lose weight, or unintentionally due to chaotic work schedules.
However, given that it is pretty easy and low-risk to grab a snack before heading out to the supermarket, this may seem like a sensible thing to do – it may have the benefit of subtly changing the foods you buy and consume throughout the week.
If you are trying to lose weight or eat a healthier diet, it may be a good idea to plan your shopping in advance. Options include using an online grocery site or, for a more low-tech equivalent, a good old-fashioned shopping list.
The NHS Choices 5 A DAY meal planner can also help you plan your weekly shop.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.