Cutting back on a high-meat diet could be good for the planet and good for ourselves, a major international scientific review suggests.
Published in the journal Science, the review noted that meat offered an important source of nutrients, but consuming large amounts increased the risk of some types of disease.
Although teasing out other factors such as smoking and obesity could be tricky, large-scale studies of Western countries had linked high-red and processed meat intake with greater death rates and some diseases.
The review indicated a shift from high meat to more plant-based diets might even reduce global mortality rates by 6-10 per cent.
When it came to the environment, meat production resulted in more greenhouse gas emissions per unit of energy, compared with plant-based foods.
The University of Oxford researchers behind the review also pointed to global impacts on water allocation and rainforest conversion for agricultural purposes.
While changing peoples' meat consumption would be a challenge, they suggested solutions could lie in environmental certification programmes, or "fiscal interventions" such as higher taxes on meat.
The review comes fresh after Air New Zealand's offering of the plant-based Impossible Burger sparked debate around the future of meat - and just days before scientists meet in Auckland for a conference exploring the impact of meats grown from proteins and self-producing cells.
Dr Cristina Cleghorn, a senior research fellow at the University of Otago who co-authored a recent paper on the health benefits of eating less red and processed meat, argued that a diet change could ease pressure on the New Zealand health system.
"It is possible for people to meet their nutritional needs without consuming meat and substantial reductions in meat intake would have a net positive impact on health."
Cleghorn noted the World Cancer Research Fund recommended that people who eat red meat should consume less than 500g each week, while the Global Burden of Disease project suggested people eat no more than 100g a week.
Professor Robert McLachlan, of Massey University's Centre for Sustainable Futures, highlighted the new review's conclusion that eating processed meat brought a higher risk of bowel cancer - something widely publicised here last year.
"It's highly relevant as bowel cancer causes about 4 per cent of all deaths in New Zealand, high by world standards."
As global demand for meat was expected to double by mid-century, pressure on meat production to become sustainable was also likely to increase, McLachlan said.
"In order to generate health and climate co-benefits, New Zealand could consider introducing an agricultural greenhouse gas tax, health and sustainability warning labels on meats and promotional campaigns to decrease meat consumption."
While the review cited "major vested interests" and "centres of power" as being barriers to such shifts, McLachlan was encouraged that red meat consumption in New Zealand had fallen by two thirds in just a decade, to the point where it was now close to both the average for rich nations and recommended health limits on a population basis.
Beef and Lamb New Zealand head of nutrition Fiona Greig noted the review acknowledged red meat provided a good source of nutrients, and diets low in meat may have negative health impacts when meat substitutes weren't available.
"In New Zealand, this reinforces beef and lamb provide an efficient and sustainable source of essential nutrients to the diet, which can address nutrient intake needs and nutrient deficiencies including zinc, iron and vitamin B12."
Greig also pointed out the review's finding that assessing the environmental impact of diets was complex, given the wide range of agricultural systems around the world, and the foods we eat.
"The review highlights that in general, recommended diets ... have a lower environmental impact than what is typically eaten, largely due to an over-consumption of food energy."