Harper, H. & M. HallsworthCounting Calories: How under-reporting can explain the apparent fall in calorie intake

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Hugo Harper & Michael Hallsworth

Release date:
August 2016

Behavioural Insights Team (BIT)

Recently, several reports and media articles have noted that official statistics show a large decline in calorie consumption in the UK over the last 40 years. At the same time, we have seen the population gain weight over this period. How has weight gone up, if we are eating less? One response is that physical activity levels must have declined, leading us to expend much less energy. But this conclusion is at odds with the consensus of expert opinion, which points to rising calorie intake as the main cause of obesity. This question has major policy implications: the two schools of thought imply different approaches. One says that reducing calorie intake should be central to any obesity strategy; the other that calorie intake is falling without government activity, and therefore the rationale for policies aimed at reducing consumption is weak. This report concludes that it is not plausible that large falls in calorie consumption, offset by even greater falls in physical activity, have caused the rise in obesity. Instead, the authors propose that the apparent fall in consumption can be explained by an increase in underreporting of calorie intake in official statistics. In other words, calorie intake may not actually have declined.

Specifically, the authors conclude that:

  1. National surveys are under-estimating our true calorie intake.
  2. Reductions in physical activity do not provide a realistic explanation for the change in weight.
  3. Calorie intake appears to have fallen because under-reporting in surveys has increased over time. 

The authors propose five main reasons why under-reporting may have increased:

  • increasing levels of obesity (since obese people are more likely to under-report their intake)
  • increased desire to lose weight (since this is associated with increased underreporting)
  • increased snacking and eating outside of the home
  • falling survey response rates
  • a growing discrepancy between reference data (used to calculate calories) and true portion sizes or food energy density.

Together, these factors point towards a serious increase in under-reporting. Finally, a trend to reduced food wastage suggests that people are consuming a larger proportion of the food they report purchasing. The first conclusion is that policies to reduce calorie consumption have an important part to play in an obesity strategy. Although attempts to increase physical activity should be part of the policy mix for obesity, they should not act as a distraction from the central importance of reducing calorie consumption.

The second conclusion is that we need to revisit our methods for creating official statistics on calories. It may be possible, for example, to recalibrate current measures using estimates of under-reporting, as set out in this paper. We should also make wider use of DLW measures, in order to get more sophisticated estimates of under-reporting. In the context of the government’s childhood obesity strategy, ensuring we have accurate measures of calorie intake is especially important: we need reliable measures for assessing the success of measures to reduce consumption.

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