12 January - 20 June 2016

Are we underestimating our calorie intake?

New data from the Office of National Statistics (ONS) suggests that UK adults are underestimating their calorie intake by one third. The report, heavily cited by the media, is part of the Evaluating Calorie Intake for Population Statistical Estimates Project (ECLIPSE), research from the ONS’s Data Science Campus aimed to compare energy intake estimates using doubly labelled water (DLW) with estimates from self-reporting data.

New data from the Office of National Statistics (ONS) suggests that UK adults are underestimating their calorie intake by one third.  The report, heavily cited by the media, is part of the Evaluating Calorie Intake for Population Statistical Estimates Project (ECLIPSE), research from the ONS’s Data Science Campus aimed to compare energy intake estimates using doubly labelled water (DLW) with estimates from self-reporting data. DLW is a method of measuring energy expenditure, and estimating consumption.  The report notes it is a costly process but is the gold standard for estimating calorie intake in nutrition studies.

The report notes that estimating calorie intake is “challenging”.  This is due to a number of contributing factors such as the nutritional content of a given meal is dependent on ingredients used to make it, cooking methods and portion size amongst others.  Data for 4452 adults aged 19 years old and over was extracted from the National Diet and Nutrition Survey (NDNS).  The data, collected between 2008 and 2014, contained information on energy intake from self-reporting diet, as well as demographics and anthropometric measurements.  A sub group of 197 participants had biometric data from DLW tests. 

The mean estimated energy intake across all survey years, using self-reported data was 2065 calories for men and 1570 calories for women.  However the average energy intake using the DLW method revealed that men consumed 3119 calories and women 2393 calories across the survey period. Data suggested that calories were declining over the survey years, however the report suggest that this could be explained by an increase in under-reporting.  Average reporting error across all adults in the sample was found to be 32%.  The report notes that self-reported intake, weight, age and gender were all significantly associated with reporting errors, with data showing that the more a person weighs the more likely it is that they understate their calorie intake. It notes that “weight was found to be associated with a level of under-reporting, this could be explained by a requirement for more calories to maintain energy balance and therefore error in the population increases as the weight of the population increases.”  However, as DLW is carried every two years it is difficult to know whether under-reporting has increased or not.

The report has a number of limitations including “DLW does not measure the same physiological processes captured in food consumption diaries”. It assumes a number of things including that individual weight is in homeostasis and subjects were not dieting; dietary behaviour is consistent throughout as DLW tests were carried out at a different time to the food diaries; and individuals in the DLW represent the total population, and the subset doesn’t differ from the remaining sample. 

The media has reported that Public Health England has responded to the report stating that underestimating is always an issue for diet studies.  It reports that PHE will be looking at overall calorie consumption when it updates its obesity strategy in March.  It is thought that the new One You Campaign will encourage adults to consumer a ratio of 400-600-600 for their main meals.

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