Britons are under-reporting their daily calorie consumption - potentially misleading policymakers attempting to curb obesity, research suggests.
The Behavioural Insights Team points to scientific and economic data showing people eat 3,000 calories, compared to the 2,000 cited in official surveys.
It says this could explain rising obesity levels, despite decades of surveys saying people are eating less.
Government statisticians say the way calorie data is collated will change.
'Tracking snacks'
Several official surveys, including the National Diet and Nutrition Survey and the Living Costs and Food Survey, suggest the amount of food people eat and buy has gone down in recent decades - while obesity rates continue to rise.
But the researchers from the Behavioural Insights Team (BIT) say if the calorie counts in these surveys were correct, the UK population would be losing weight overall.
The BIT is an independent company but started its life in 2010 as a government policy group known as the "nudge unit" because it was tasked with encouraging people into making better life choices.
Its study points to scientific studies including chemical analysis of how much energy people burn, that show people are eating about 1,000 more calories a day per person than surveys would suggest.
National spending figures also suggest we are buying more food than we report in surveys, the authors say.
They suggest there could be many reasons people are not accurately reporting what they eat, including snacks being difficult to track, a desire to lose weight making them less likely to be honest about their eating habits, and fewer people taking part in the surveys overall.