Are you aware of the silent obstacle hindering nutritional research? “Under-reporting of food intake is one of the fundamental obstacles preventing the collection of accurate habitual dietary intake data,” a pervasive issue affecting large nutritional surveys, with prevalence ranging from 18% to 54% and sometimes as high as 70% in specific subgroups. This phenomenon, once described as the “nutritionists’ guilty secret,” is now being openly addressed as a priority research area.
This insightful review, “Assessing dietary intake: Who, what and why of under-reporting,” delves deep into the complexities of this critical problem, highlighting its significant impact on our understanding of diet-disease relationships, particularly in the context of obesity. For years, self-reported data misleadingly suggested obese individuals ate less, implying a metabolic defect rather than excessive intake. Advanced techniques like doubly labelled water (DLW) have since revealed the opposite, casting doubt on self-reported dietary accuracy, especially among the obese.
Key insights from this vital research include:
- Who is Under-Reporting?
- Women are consistently more likely to under-report than men. This may be linked to societal pressures on women to conform to images of “femininity” and concern about body weight.
- Overweight and obese individuals are frequently identified as under-reporters. For instance, one study found under-reporting to be as high as 71% in overweight women. Social stigmatization and the pervasive “dieting obsession” in Western societies may drive this behavior, with individuals potentially using study participation as an opportunity to diet.
- Other characteristics with less consistent evidence include age (older individuals), lower levels of education, smoking habits, social class, physical activity, dietary restraint, and emotional states.
- What is Being Under-Reported?
- It is challenging to determine if under-reporting is specific to macronutrients or certain foods, as most methods primarily identify low energy intakes.
- Studies suggest that carbohydrate (especially sugar) tends to be under-reported, while protein is often accurately reported or even over-reported. The accuracy of fat intake reporting remains unclear.
- A logical conclusion, supported by evidence, is that food items with a negative health image (e.g., cakes, sweets, confectionery, high-fat foods) are more likely to be under-reported, whereas those with a positive health image (e.g., fruits and vegetables) may be over-reported.
- Snack foods are particularly susceptible to under-reporting, possibly due to their negative association with weight gain or simply being forgotten or deemed inconvenient to record.
- Why Do People Under-Report?
- Under-reporting is complex, stemming from both intentional and unintentional factors.
- Intentional reasons include:
- Social Pressure/Desirability: Individuals may alter their records to convey a socially desirable image, driven by embarrassment or a desire to conform to perceived norms.
- Inconvenience: Completing food records can be time-consuming and burdensome. Subjects may omit foods or alter eating patterns because it’s “too much hassle”.
- Unintentional reasons include poor memory, poor attention, and literacy problems. Genuine under-eating due to illness or dieting can also be mistaken for under-reporting.
The authors emphasize that resolving this issue requires a multidisciplinary approach, incorporating insights from psychology, sociology, and physiology, in addition to nutrition and epidemiology. While there are no simple solutions, acknowledging the problem and integrating physiological parameters with psychological understanding will significantly enhance the validity and confidence in dietary data.
Reference for the article:
Macdiarmid, J., & Blundell, J. (1998). Assessing dietary intake: Who, what and why of under-reporting. Nutrition Research Reviews, 11, 231-253.
