London Cyclists by Alexander Baxevanis CC2.0

Photo: London Cyclists by Alexander Baxevanis/Flickr, CC2.0

Being more physically active and having a healthier diet can reduce our chance of becoming ill and dying prematurely. New research undertaken undertaken by the Centre for Diet and Activity Research (CEDAR) in collaboration with Dr Christian Brand at TSU has been published in BMJ Open and helps us to quantify these benefits following small changes in behaviour.

Both replacing short car trips with cycling and eating more fruits and vegetables thousands of premature deaths per year could be prevented. However, these changes would not just have effects on health - but also the environment and consumers’ wallets. Understanding these costs and benefits will help to quantify the health, consumer and climate impacts of various active travel and diet scenarios - and can help to create better public health policies.

Physical activity and diet - beyond health

Previous research has shown that regular physical activity reduces the risk of diseases such as diabetes, heart disease, and several cancers. One way for people to increase their levels of physical activity is through active travel - for example cycling. Replacing short car trips with cycling also reduces fuel costs and greenhouse gas emissions. Similarly, having a diet rich in fruits and vegetables has been shown to reduce the risk of diseases such as heart disease, stroke, diabetes and some types of cancer. Therefore national campaigns like "5 a day" (or now "10 a day") encourage people to consume at least five portions of fruit and veg per day to reduce their risks for these diseases. However, producing fruits and vegetables will create greenhouse gas emissions and buying them might increase consumer costs, unless fruits and vegetables replace other food items.

When comparing different travel scenarios, the researcher found out that:

  • Replacing all trips of 1 mile or less currently taken by car would prevent an estimated 75 premature deaths per year in England.
  • Benefits would increase rapidly to 800 death prevented per year if all car trips less than 2 miles long were done by bicycle. This would rise to 2300 deaths prevented for trips less than 3 miles. Replacing all trips less than 8 miles long would prevent 7500 deaths per year.
  • Changes to travel would benefit high- and middle-SES groups the most because these people tend to use the car more for shorter trips. Similarly, fuel costs savings accrued more to people in the highest SES group. This means that such a shift would be unlikely to decrease health inequalities, although it would generate sizable health benefits overall, by reducing mortality.
  • Replacing all trips of 1 mile or less currently taken by car would decrease transport related greenhouse gas emissions 0.3%, and replacing all trips of 8 miles or less would decrease transport related emissions 19%. As transport was the only sector that increased greenhouse gas emissions between 2013 and 2015, more actions are needed to reduce emissions from that sector.

When comparing different diet scenarios, the researchers find out that:

  • Increasing fruit and veg by one portion per day, such as an apple a day, would prevent 3300 deaths per year.
  • Benefits would increase to 6200 deaths prevented each year if everyone ate at least five portions of fruit and veg per day, or if everyone ate five portions of fruit and veg more per day (in addition to what they already eat).
  • These changes would mainly benefit people in lowest SES group as they tend to eat less fruit and veg, decreasing health inequalities in the population. However, this would also substantially increase consumer costs (34% for five portions of fruit and veg per day scenario) for the lowest SES group when compared to average food purchase cost of this group. Thus, in proportion the cost of fruits and vegetables is higher for lowest SES group, although they would benefit from this change most.
  • The greenhouse gas emissions would also increase substantially (4% to 39% increase in agriculture related greenhouse gas emissions). However, we assumed that eating more fruit and veg would not replace other food items. If eating vegetables would replace for example meat, then greenhouse gas emissions would decrease because producing meat generated more emissions than producing vegetables.

Methods - health modelling

To compare potential health consequences of physical activity and diet scenarios, researchers used computer modelling to quantify changes in mortality, consumer costs and emissions of replacing short car trips with cycling and increasing consumption of fruit and veg for working age adults (20-69 years). Mortality and consumer costs changes were estimated separately for groups of different socioeconomic status (SES) using a national, occupation-based classification system (National Statistics Socio-economic Classification). By doing so, the researchers could quantify changes in health benefits and consumer cost overall and for three SES groups (high, medium and low) to see if these changes would also decrease health inequalities by improving the health of people in lowest SES. This study is the first that modelled the health, cost and greenhouse gas emission impacts of both physical activity and improved diet for different SES groups in England.

The main sources for this research were the National Travel Survey (NTS), the Health Survey for England (HSE) and the National Diet and Nutrition Survey (NDNS).