A diet of more fruit and vegetables and less meat could reduce greenhouse gas emissions by nearly a fifth and extend average life expectancy by eight months, according to research.
Scientists at the London School of Hygiene & Tropical Medicine said eating better would benefit people's health and the environment.
The diets of the average man and woman in Ireland and the UK do not currently conform to World Health Organisation (WHO) recommendations, but its study suggested that if they did, greenhouse gas emissions would be reduced by 17pc.
Researchers analysed food diaries from more than 1,500 adults in Britain and looked at how diet related to health problems such as coronary heart disease, stroke, type 2 diabetes and a number of cancers.
They said diet-related ill-health costs Britain's health service £6bn (€8bn) a year, but calculated that eating more healthily could save almost seven million years of life lost prematurely over the next 30 years.
They estimated that it would also extend average life expectancy by around eight months (12 months for men and four months for women).
"Eating fewer animal products and processed foods and more fruit and vegetables would produce benefits to both health and the environment," the researchers said.
They added that "radical" dietary changes such as veganism were not necessary in order for there to be large reductions in emissions and benefits to health.