“Planet-friendly” foods may also help reduce a person’s risk of death from cancer, heart disease and other chronic illnesses by 25%, researchers have said.

Scientists in the US found those who followed a sustainable diet of more plant-based foods – such as whole grains, fruit, vegetables and nuts – were less likely to die over the course of 30 years compared with those who ate less environmentally friendly meals.

Based on their findings, presented at Nutrition 2023 – the annual meeting of the American Society for Nutrition in Boston, Massachusetts – the researchers have developed a new diet score that shows the effects of food on human health as well as the environment.

Known as the Planetary Health Diet Index (PHDI), it looks at existing evidence to give scores for foods.

The index takes into account the risk of chronic illnesses such as heart disease, bowel cancer, diabetes and stroke, as well as environmental impacts such as water use, land use, nutrient pollution and greenhouse gas emissions.

The team said their work builds on existing research which shows plant-based foods are healthier and less harmful to the planet than red and processed meats.

The researchers are hoping this tool will help policymakers and public health bodies develop strategies to improve public health while also addressing climate change.

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Linh Bui, a PhD student in the Department of Nutrition at Harvard University’s TH Chan School of Public Health, said: “We proposed a new diet score that incorporates the best current scientific evidence of food effects on both health and the environment.

“The results confirmed our hypothesis that a higher Planetary Health Diet score was associated with a lower risk of mortality.”

After developing their tool, the researchers used it to determine and observe the outcomes of more than 100,000 people in the US, from 1986 to 2018.

More than 47,000 died during the follow-up period of more than 30 years.

The team found that higher PHDI scores were associated with a 15% lower risk of death from cancer or heart diseases, a 20% lower risk of death from neurodegenerative diseases, and a 50% lower risk of death from respiratory diseases.

Ms Bui said the PHDI may need to be adapted for different countries, depending on their culture or religion.

She also cautioned those with specific health conditions or food accessibility issues may find a planet-friendly diet more challenging.