Life
    Health

    Don’t dismiss the data: a fatter Britain really is consuming fewer calories

    9 August 2016

    Three years ago, a study found that people in Britain drink considerably more than they say they do. It became an international news story even though it is common knowledge among researchers that drinkers greatly under-report their intake.

    This week a report found that people in Britain eat considerably more than they say they do. This, too, has received an enormous amount of news coverage despite the fact that anybody who has spent more than five minutes with the data knows that under-reporting is endemic in this area too.

    In the case of alcohol, we don’t need surveys to tell us how much we’re drinking because we’ve got the tax receipts. All we have to do is estimate how much has been spilled or abandoned and we can work out average intake with relative ease.

    Food is more difficult. We have surveys showing what people say they eat and we have surveys showing what people say they bought, but people cannot be trusted to recall what they have eaten and a lot of food is thrown away. If we took the Living Costs and Food Survey at face value, the average Briton eats only 2,192 calories a day. This is implausible when 25 per cent of us are obese. (The government recommends men and women eat 2,500 and 2,000 calories a day respectively).

    All sources are agreed on one point, however: we are eating fewer calories as a fat nation than we did as a slim nation. World War Two rations were designed to give civilians 3,000 calories a day. In the late 1940s, scientists found that people lost weight if they got less than 2,900 calories a day. A survival diet 70 years ago would be an obesogenic diet today.

    It is safe to assume that calorie consumption rose when rationing ended, although statistics are thin on the ground until the Living Costs and Food Survey started up in 1974. In its first year, this survey reported that 2,534 calories per day were consumed in the home (it did not look at eating out). By 2012, with eating out now included, this had fallen to 2,192 calories.

    The exact numbers found in these surveys are misleading due to under-reporting, but the trend is clear. The Institute for Fiscal Studies has written about these data before, as have I for the Institute of Economic Affairs. Not everybody is convinced, however. The Behavioural Insights Team — commonly known as the Nudge Unit and now privatised — yesterday released a report claiming that ‘calorie consumption has not significantly decreased over time’.

    Their argument is that under-reporting is endemic and has got worse in recent decades. They suggest several reasons why people today might be more inclined to forget or lie about what they have eaten, such as the tendency of obese people to under-report more than slim people and the general awareness of obesity as a health issue. These are worthwhile considerations and I agree that they have played a part, but researchers are well aware of them (they are mentioned in both the IFS and IEA reports). In my view, it is very unlikely that they can explain all of the self-reported decline in calorie consumption, let alone that they have masked a rise in calorie consumption. The self-reported decline is just too steep.

    With the exception of the mavericks at Public Health Collaboration, nobody seriously believes people are consuming 400 fewer calories than they did in 1974. The question is whether we are eating more calories than they did back then. The Nudge report accepts that we are not. Instead it says that, after correcting for under-reporting, ‘the decline since 1974 is a lot smaller than previously stated — around 200kcal per day compared to around 400kcal’.

    This is a significant admission. Given that obesity rates were very low in the 1970s, it leads to the obvious conclusion that a decline in physical activity, not an increase in food intake, has driven the rise in obesity. But this is the opposite of the Nudge Unit’s thesis and so they spend several pages trying to debunk the notion that people are less physically active than they used to be.

    This is the weakest part of the report because they resort to a tactic used by our old friend Aseem Malhotra and use leisure time exercise as a proxy for physical activity. Surveys show an increase in the number of people who follow the Chief Medical Officer’s recommendation of exercising for 30 minutes five times a week. The data-set only goes back to 1997 and the Nudgers acknowledge that it contains the same kind of self-reported figures that they have just criticised, but that is only part of the problem. There is no contradiction between a third of the population taking part in regular leisure time exercise and a quarter of the population being obese. They are not the same people.

    Moreover, people only exercise in their spare time when they are not getting enough physical activity in their daily lives. People did not need to go to the gym 70 years ago because they had naturally active lifestyles. Sure enough, there are figures tucked away in the appendix of the Behavioural Insights Team’s report showing that men expend 100 fewer calories at work today than they did in the early 1980s. Combine that with the rise in car ownership, the decline of walking and the rise of labour-saving devices and it is easy to see why physical activity has declined by 24 per cent since the 1960s, as Public Health England says it has.

    Despite torturing the data, the Nudge Unit team fails to extract a confession. After throwing everything they can at the statistics, the best they can manage is the claim that calorie consumption has not fallen as much in the last 40 years as a naive interpretation of food surveys might suggest. But we are already knew that, just as we know that people drink a lot more than they say they do. The fact remains that calorie consumption has fallen over the long term and so has physical activity. If, as the Nudge Unit admits, we are eating fewer calories than we did in the 1970s, a decline in physical activity is the only possible culprit.

    The authors of the report seem to believe that there are competing views on how to tackle obesity with one side claiming that it is futile to reduce calorie consumption because it has failed to reduce obesity in the recent past. I’m not sure that is true. It is certainly not my position. Reducing calorie consumption is as valid an approach as increasing physical activity. Indeed, reducing calorie consumption might be a more realistic option for many people. Whether the government has the ability or mandate to reduce calorie consumption is another issue, but regardless of where you stand on that question we should not rewrite history. The notion that obesity started rising after 1980 because the nation was consuming more and more calories remains a myth.