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Answering seems simple enough. For many people however, the need to avoid criticism and seek praise causes them to respond in a manner consistent with expected norms. Self-reports of dietary intake can be biased by these tendencies, tainting consumption data collected by the health community. Everyone knows they should eat five or more servings of fruits and vegetables a day, so that’s what they say when they’re asked — many even really believe it to be true.
The findings, published in the Nutrition Journal, demonstrate that self-reports of fruit and vegetable consumption are susceptible to substantial social approval bias . Such biases are the presence of social desirability (the tendency to respond in such a way as to avoid criticism) and social approval (the tendency to seek praise) [2-3].
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Researchers from the University of Colorado Denver randomly selected 163 women to complete what they were told would be a future telephone survey about health. Randomly half the women were sent a letter prior to the interview describing it as a study of fruit and vegetable intake. Included with the letter was a brief statement on the benefits of fruit and vegetable consumption, a 5-A-Day sticker and a 5-A-Day refrigerator magnet. The other half of the women in the study recieved the same letter but it described the study purpose only as a more general nutrition survey and contained neither the fruit and vegetable message nor the 5-A-Day materials.
Within 10 days of receiving the letters, each of the women answered a food frequency questionnaire and were asked how many fruits and vegetables they had eaten in the last 24 hours.
Since the two groups were randomly selected, fruit and vegetable consumption should have been the same in each group. However, those women that recieved the fruit and vegetable message and the 5-A-Day materials reported a significantly higher intake of total fruits and vegetables, and 40% of individuals were categorized as eating 5 or more servings of fruits and vegetables a day compared to just 18% in the other group.
In response to the 24-hour recall questions, 61% of women who received the fruit and vegetable message and the 5-A-Day materials reported eating fruits and/or vegetables on three or more occasions throughout the previous day compared to 32% in the other group. These percentages were independent of age, race, educational level, self-perceived health status and time since last medical check-up.
According to the authors of the study :
This study therefore suggest that social approval bias might well be a substantial problem in the interpretation of nutritional intervention effects that are dependent on education and awareness to affect behavior change. The magnitude of this bias is similar to the intervention effects reported in many studies evaluating changes in fruit and vegetable intake (ranging from 0.93 to 1.25 servings per day). Thus, a major challenge facing nutritional intervention researchers is assessing true behavioral change based on self-reports from reporting bias.
This doesn’t mean that health questionnaires are useless. Rather, it means that many people simply aren’t being entirely truthful when it comes to how many fruits and vegetables they eat. The authors suggest that, in large dietary intervention trials, subgroups can be evaluated with biomarkers or other independent assessments to estimate the reporting bias size. Additionally, bias can also be controlled to some degree by assessing different intensities of an intervention, whereby everyone receives at least a minimal prompt for change instead of one group not receiving any prompt at all.
A growing body of evidence shows that fruits and vegetables are critical to promoting good health. Here’s 5 tips to help you eat more:
- Keep fruits and vegetables on the counter or at eye level in the refridgerator. Make them easy to find and you’ll be more likely to eat them.
- If you’re worried about fruits and vegetables spoiling, try canned and frozen fruits and vegetables.
- Eat fruits and vegetables at every meal. For snacks, try carrot sticks, raisins or apple slices.
- Buy precut fruits and vegetables. They may cost a bit more than unprepared fruits and vegetables, but there’s less work and they’re ready to eat.
- Skip the potatoes. They have a high glycemic index compared to other vegetables such as broccoli, cauliflower, asparagus, string beans or peas.
Fruits and vegetables contain essential vitamins, minerals and fiber. In addition to the numerous health benefits of eating more fruits and vegetables, increased consumption lowers your risk of developing several cancers.
How about you? Do you lie to yourself about the fruits and vegetables you eat?
Miller et al. Effects of social approval bias on self-reported fruit and vegetable consumption: A randomized controlled trial. Nutr J. 2008 Jun 27;7(1):18. [Epub ahead of print] DOI: 10.1186/1475-2891-7-18
Hebert et al. Social desirability bias in dietary self-report may compromise the validity of dietary intake measures. Int J Epidemiol. 1995 Apr;24(2):389-98.
Hebert et al. Gender differences in social desirability and social approval bias in dietary self-report. Am J Epidemiol. 1997 Dec 15;146(12):1046-55.