Martin O’Connell: Why lower calorie counts have led to bulging waistlines

By 2011 over a quarter of UK adults were classified as obese and 70 per cent as overweight. When faced with these facts, people often are led to conclude that we, at least on average, must be eating more.

The surprising conclusion of a recent study by researchers at the Institute for Fiscal Studies (IFS) is that, in fact, the total number of calories that households in England purchase has fallen starkly since 1980.

Exploiting a Government survey which records in detail what households purchase over a two week period, the research shows that falls in calorie purchases range from around 15 per cent for single over 50s to 27 per cent for couples with children.

The simultaneous increase in waistlines and fall in calories raises a puzzle. How can people be eating less but getting heavier?

Part of the explanation is likely to be a shift to more sedentary lifestyles.

Our working life, for instance, is now much more likely to involve sitting in front of a computer than the more active occupations of the past.

So while calories ingested are falling, the number of calories many of us burn through physical activity has also declined.

It is also noteworthy that these substantial declines in total calorie purchases have happened at a time when people have increased how much food they buy from restaurants and takeaways, and in the form of confectionery and soft drinks. This shift in the source of calories may also be important in explaining changes in diet related disease.

A second, complementary IFS study takes a more detailed look at changes in the food purchases a sample of British households have made over the recent recession. Since 2008 prices have increased faster than wages and unemployment has increased, squeezing households’ disposable incomes. The recession followed large increases in world food prices. From 2007 to 2012 the price of food rose by 10.2 per cent more than the price of all goods (according to the consumer price index – the leading measure of household inflation).

Over this period food spending in cash terms has failed to keep pace with rising food prices. Households have responded by continuing their long run switch to buying fewer calories. But they have also chosen to switch to cheaper calories. This is a significant break with past behaviour and bucks a long run switch towards higher spend per calorie dating back to 1980.

Switches to cheaper calories may not necessarily adversely affect nutrition. People may be able to reduce their per calorie spend by making more use of sales, by spending more time shopping in search of better value, or by buying larger pack sizes – which tend to be cheaper per kilogram – of the same produce. But a second way to reduce spend per calorie is to switch to cheaper and less nutritious calories – by switching from lean mince to standard mince, for example.

The IFS research also documents a switch to calories that are less nutritious. Households have moved away from fresh fruit and vegetables and towards processed foods, and as a result, the average saturated fat and sugar content of food purchases has increased.

Pensioner households, couples with children aged less than 10 and lone parent households show larger average falls in the nutritional quality of their calorie purchases than other household types. This does not prove conclusively that cut backs in spend per calorie are causing poorer diet, but it certainly suggests that further research into whether this is the cause could prove valuable.

Whether recent cutbacks in spend per calorie and in nutritional quality represent the beginning of new long run trends, or whether people will revert back to more expensive and nutritious calories in the future, is an open question.

Overall this research highlights that links between food purchases and diet-related health problems such as obesity are complex. Understanding these links involves considering other aspects of people’s lifestyles and, in particular, the inter-action between diet and physical activity.

And the economic environment in which people make their consumption decisions cannot be ignored. Changes in household incomes, rises in world food prices, and movements in the relative price of processed and fresh food will all feed into influencing diets. The more we can understand about how these factors interact, the better able we are to assess policies that aim to combat diet-related disease.

* Martin O’Connell is a senior research economist at the Institute for Fiscal Studies.