By being more physically active and having a healthier diet, we can reduce our chance of becoming ill and dying prematurely. However, the impact of individuals’ behaviour can be difficult to measure in populations. New research published in BMJ Open by researchers from CEDAR, MRC Epidemiology Unit and the University of Oxford is helping us find out how much these small changes in behaviour could improve our overall health.

The research shows that, by replacing short car trips with cycling and eating more fruits and vegetables, thousands of premature deaths per year could be prevented. However, as well as the effects on health, these changes also have an impact on the environment and on consumers’ wallets. Understanding these costs and benefits will allow us to better quantify the total impacts of various active travel and diet scenarios – and help support better public health policies.

Physical activity and diet – beyond just health

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. However, unless we cut down on meat at the same time, growing more vegetables will create greenhouse gas emissions. Also, buying more fruit and veg could increase costs for consumers.

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).

Changes for mortality and consumer costs were estimated separately for groups of different socioeconomic status (SES) using a national, occupation-based classification system (the National Statistics Socio-economic Classification). This allowed the researchers to quantify health benefits and consumer costs for the whole population, and also see if changes might affect lower SES groups more or less than higher ones. This study is the first that has modelled the health, cost and greenhouse gas emission impacts of both physical activity and improved diet for different SES groups in England.

Many benefits, but some downsides too

When comparing different travel scenarios, the researchers found that:

• Replacing all trips of one 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 two miles long were done by bicycle. This would rise to 2300 deaths prevented for trips less than three miles. Replacing all trips less than eight 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 would be greatest for those 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 one mile or less currently taken by car would decrease transport related greenhouse gas emissions 0.3 percent. Replacing all trips of eight miles or less would decrease transport related emissions by 19 percent. For comparison, in the Climate Change Committee’s Reducing emissions and preparing for climate change: 2015 Progress Report to Parliament, transport was the only sector that increased greenhouse gas emissions between 2013-14, indicating that more actions are needed to reduce emissions from that sector.
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When comparing different diet scenarios, the researchers found that:

• Increasing fruit and veg by one portion daily – just an apple a day – would prevent 3300 deaths per year.
• Benefits would increase to 6200 deaths prevented each year if everyone ate five portions of fruit and veg more per day.
• These changes would mostly benefit people in the lowest SES group as they tend to eat less fruit and veg. This could help reduce health inequalities in the population. However, this would also substantially increase consumer costs for the lowest SES group when compared to average food purchase cost of this group. For this group, there would be a 39 percent increase in daily, average food and non-alcoholic drinks costs if they would buy five portions of fruits and vegs more per day.
• Greenhouse gas emissions would also increase substantially if everyone ate five portions of fruit or veg more per day (a 22 percent increase in agriculture related greenhouse gas emissions from England). However, this would only be the case if eating more fruit and veg did not replace other foods. If vegetables replaced meat in diets, then greenhouse gas emissions would decrease because of the high carbon impact of rearing meat compared to growing vegetables.
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A recipe for a healthier and more equal society?

This modelling study suggests that while policies that encourage people to switch from their car to active transport for short journeys or to eat more fruit and vegetables have clear positive impacts on the overall health of the population, the picture is more mixed when it comes to environmental benefits and reducing social inequality. To minimise the risk that such public health measures increase social and economic inequality, policies to encourage active transport or fruit and vegetable consumption need to take into account the financial burden and the potential burden on the planet.

Notes

• Read the full paper: Tainio et al. Mortality, greenhouse gas emissions, and consumer cost impacts of combined diet and physical activity scenarios: A Health Impact Assessment study. BMJ Open, DOI: 10.1136/bmjopen-2016-014199
• The principal data sources for this research were the National Travel Survey (NTS), Health Survey for England (HSE), and the National Diet and Nutrition Survey (NDNS).