A new diet is being hailed as "life-saving" by experts, but there's a catch...you can only eat red meat once a week.

That's as much red meat people should eat to do what's best for their health and the planet, according to a report seeking to overhaul the world's diet.

The report from a panel of nutrition, agriculture and environmental experts recommends a plant-based diet, based on previously published studies that have linked red meat to increased risk of health problems. It also comes amid recent studies of how eating habits affect the environment. Producing red meat takes up land and feed to raise cattle, which also emit the greenhouse gas methane.

Associate professor at Massey Universty, Carol Wham, told Tim Dower this will be a real reality check for people.

"What it is doing is saying globally this is what we might need to reach by the year 2050."

"For us in New Zealand, it's about moderating our meat, it's about primarily reducing excessive consumption and what it says instead, is that we need to double our consumption of fruit, vegetables [and] things like legumes and nuts which we really eat insufficient amounts of."

"Our dietary fibre intakes are woefully low so eating a more plant-based diet has huge benefits for us."

She said it's all about "moderation over time" and getting creative with how you cook.

"There's nothing like slicing up the BBQ meat to put on Thai beef salads and things like that."

Wham said while New Zealand isn't the focus of the study, it's still important we do our bit.

"This is just looking globally at what it has to look like if we are going to have a sustainable system in the future and health of people and the planet."

"We can't keep going the way we are, we have got such an epidemic of obesity. In the US for example, they produced twice the amount of food than they need to eat."

John Ioannidis, chair of disease prevention at Stanford University, said he welcomed the growing attention to how diets affect the environment, but that the report's recommendations do not reflect the level of scientific uncertainties around nutrition and health.

"The evidence is not as strong as it seems to be," Ioannidis said.

The report was organized by EAT, a Stockholm-based nonprofit seeking to improve the food system, and published Wednesday by the medical journal Lancet. The panel of experts who wrote it says a "Great Food Transformation" is urgently needed by 2050, and that the optimal diet they outline is flexible enough to accommodate food cultures around the world.

Overall, the diet encourages whole grains, beans, fruits and most vegetables, and says to limit added sugars, refined grains such as white rice and starches like potatoes and cassava. It says red meat consumption on average needs to be slashed by half globally, though the necessary changes vary by region and reductions would need to be more dramatic in richer countries like the United States.

Convincing people to limit meat, cheese and eggs won't be easy, however, particularly in places where those foods are a notable part of culture.