Greater adherence with a diet rich in vegetables, low fat dairy and whole grains is not only good for health but also good for the planet, according to a study by researchers at Cambridge and Oxford Universities.

The Dietary Approaches to Stop Hypertension (DASH) diet is a proven way to prevent and control hypertension and other chronic disease such as type 2 diabetes and certain cancers. New analysis, published in the American Journal of Clinical Nutrition shows that this diet is also associated with lower emissions of climate-changing greenhouse gases. However, the researchers found that keeping to the DASH diet was associated with higher food costs, and suggest that systemic changes may be needed to make healthier, low-carbon diets more affordable.

The researchers at the Centre for Diet and Activity Research (CEDAR), Cambridge University and Nuffield Department of Population Health, Oxford University analysed data on the diets of over 24,000 adults aged 39-79 in the EPIC-Norfolk UK cohort. Their dietary intake was measured against how close it accorded to the DASH diet, which emphasises vegetables, fruits, and fat-free or low-fat dairy products; includes whole grains, fish, poultry, beans, seeds, nuts, and vegetable oils; and limits salt, sugar and red meats. Researchers also uses UK data on carbon dioxide equivalents (CO2eq) associated with the production of different foods to estimate what the carbon footprint of this diet was. Finally, they looked at what these different diets cost using date from a UK-based supermarket comparison website. The association between accordance with DASH principles, greenhouse gas emissions and cost were then compared.

The researchers found that greater accordance with the DASH dietary targets was associated with lower greenhouse gas emissions. Most of the climate impact of food production is from methane emitted by ruminant animals during digestion, and nitrous oxide released from the land during tilling. In this study, diets with the highest level of accordance with DASH had a greenhouse gas impact of 5.60kg CO2eq/day compared to 6.71 kg CO2eq/day for least-accordant diets. Among the DASH food groups, higher greenhouse gases were most strongly associated with meat consumption, and lower emissions associated with whole grain consumption.

Dr Pablo Monsivais lead author of the study from the Centre for Diet and Activity Research (CEDAR), University of Cambridge said. “We already know that eating less meat reduces the carbon footprint from our diet: the challenge is to identify a healthy and ‘green’ diet that is also likely to be taken up by a large proportion of the population. DASH is less well known in the UK than it is in the United States, but because it was designed to be broadly in line with existing western eating habits, it might make it more acceptable for the UK population than other evidence-based diets that are less similar to current UK eating habits.”

One of the drawbacks of the DASH diet is its relative cost. This study found that higher accordance with the DASH diet was associated with higher dietary costs, with the average cost of diets in the highest adherence to DASH costing 18% higher than of those least adherence. This is particularly pertinent in the UK where food prices rose over 30 percent from 2007 to 2013. This trend has coincided with deterioration of diet quality, particularly among lowest-income groups.

Dr Peter Scarborough, Nuffield Department of Population Health, Oxford University added: “To help support the uptake of the DASH diet – and other healthy diets – we need to address the rising price of foods and the difference in price between healthy and unhealthy diets. This means action on various fronts including agricultural subsidies, retail pricing strategies, and potentially health-related food taxes and subsidies.”