Citerank: (12) 352521Not building exercise into daily life A primary cause of the rise in obesity in the UK in recent decades has been a decline in energy expended rather than rise in energy intake; with the changing pattern towards more sedentary lifestyles appearing to be a key factor in this.555CD992, 371563Per capita sugar consumption has fallen by 16% since 1992Evidence suggests that per capita consumption of sugar, salt, fat and calories has been falling in Britain for decades. Per capita sugar consumption has fallen by 16 per cent since 1992 and per capita calorie consumption has fallen by 21 per cent since 1974.13EF597B, 371611Changing patterns of physical activityTechnological development and urbanisation bring significant shifts in the patterns of daily activity that can reduce the amount of energy people expend in their normal daily routines.555CD992, 371615Self-reported physical activity is increasingThe number of people who are self-reporting as meeting the government's recommendation of taking 30 minutes vigorous exercise five times a week rose from 26.5 per cent to 37.5 per cent between 1997 and 2012. [3]13EF597B, 371616A minority of people are meeting the recommendationsAlthough the number of people self-reporting as meeting the government's recommendations is rising, the total number remains a minority of the population.13EF597B, 371617The recommendations relate only to leisure activitiesThe government recommendations, on which people are self-reporting, relate only to leisure activities – and other lifestyle factors (especially the increasingly sedentary patterns of behaviour) may be more significant in this context.13EF597B, 399908Not building exercise into daily life The primary cause of the rise in obesity in the UK in recent decades has not been a decline in energy expended rather than rise in energy intake; with the changing pattern towards more sedentary lifestyles appearing to be a key factor in this.555CD992, 399933Self-reported physical activity is increasingThe number of people who are self-reporting as meeting the government's recommendation of taking 30 minutes vigorous exercise five times a week rose rose from 26.5 per cent to 37.5 per cent between 1997 and 2012. [3]13EF597B, 399957A minority of people are meeting the recommendationsAlthough the number of people self-reporting as meeting the government's recommendations is rising, the total number remains a minority of the population.13EF597B, 399958The recommendations relate only to leisure activitiesThe government recommendations, on which people are self-reporting, relate only to leisure activities – and other lifestyle factors (especially the increasingly sedentary patterns of behaviour) may be more significant in this context.13EF597B, 399961Per capita sugar consumption has fallen by 16% since 1992Evidence suggests that per capita consumption of sugar, salt, fat and calories has been falling in Britain for decades. Per capita sugar consumption has fallen by 16 per cent since 1992 and per capita calorie consumption has fallen by 21 per cent since 1974.13EF597B, 399963Measuring diet at a societal level is an inexact scienceMeasuring diet at a societal level is an inexact science – as researchers generally have to rely on people keeping track of what they eat over a period of several days – and people may be inclined to under report their consumption patterns. Evidence suggests that people may throw away about 10-20% of the food they buy and underreport how much they eat by around 20–40%.8FFB597

Measuring the diet of the nation is not an exact science. Researchers rely on individuals keeping track of what they eat over a period of several days and it is well known that people tend to under-report the amount of food they consume due to a desire to deceive or - more commonly - a tendency to forget (over-reporting is also possible, though less common). The alternative method of keeping till receipts to check what food has been purchased is also problematic because some food is thrown away.

Researchers are well aware of these issues and have ways of testing the degree of under-reporting, notably with urine tests using ‘doubly labelled water’ which show how much energy a person has expended (and, therefore, how much energy a person of steady weight has consumed). Nevertheless, it is believed that Britons throw away about 10-20 per cent of the food they buy and underreport how much they eat by around 20 to 40 per cent.

Under-reporting of food intake is one of the fundamental obstacles preventing the collection of accurate habitual dietary intake data. The prevalence of under-reporting in large nutritional surveys ranges from 18 to 54% of the whole sample, but can be as high as 70% in particular subgroups. This wide variation between studies is partly due to different criteria used to identify under-reporters and also to non-uniformity of under-reporting across populations. The most consistent differences found are between men and women and between groups differing in body mass index. Women are more likely to under-report than men, and under-reporting is more common among overweight and obese individuals. Other associated characteristics, for which there is less consistent evidence, include age, smoking habits, level of education, social class, physical activity and dietary restraint. Determining whether under-reporting is specific to macronutrients or food is problematic, as most methods identify only low energy intakes. Studies that have attempted to measure under-reporting specific to macronutrients express nutrients as percentage of energy and have tended to find carbohydrate under-reported and protein over-reported. However, care must be taken when interpreting these results, especially when data are expressed as percentages. A logical conclusion is that food items with a negative health image (e.g. cakes, sweets, confectionery) are more likely to be under-reported, whereas those with a positive health image are more likely to be over-reported (e.g. fruits and vegetables). This also suggests that dietary fat is likely to be under-reported. However, it is necessary to distinguish between under-reporting and genuine under-eating for the duration of data collection. The key to understanding this problem, but one that has been widely neglected, concerns the processes that cause people to under-report their food intakes. The little work that has been done has simply confirmed the complexity of this issue. The importance of obtaining accurate estimates of habitual dietary intakes so as to assess health correlates of food consumption can be contrasted with the poor quality of data collected. This phenomenon should be considered a priority research area. Moreover, misreporting is not simply a nutritionist's problem, but requires a multidisciplinary approach (including psychology, sociology and physiology) to advance the understanding of under-reporting in dietary intake studies.

The 7.0 million tonnes of food and drink waste thrown away from our homes in 2012 is enough to fill Wembley Stadium nine times over7 . It represents 19%, by weight, of food and drink brought into the home, compared to 22% in 2007.