Indeed, if we are to have any hope of feeding 9bn people by 2050, they will have to be on a predominantly vegetarian diet, said successive speakers at day three of the event, which was held at Loma Linda University in California.

While a lot of studies have made assumptions about the environmental benefits of plant-based diets based on theoretical models, researchers at Loma Linda have been able to provide clear evidence of these benefits by analyzing real-world data on dietary patterns from the AHS-2 cohort of 96,000 seventh day Adventists living in the US and Canada, said Dr Samuel Soret, Assistant Professor and Chair - Department of Environmental Health and Geoinformatics Sciences, at the University’s school of Public Health.

Vegans’ GHG emissions were 41.7% lower than non-vegetarians’, while lacto-ovo vegetarians’ emissions were 27.8% lower ​

According to recent estimates, 80% of greenhouse gas emissions of all food production arises from livestock, claimed Samuel Soret, PhD, Professor of Environmental Health and Geoinformatics Sciences at Loma Linda University School of Public Health

Analysis of the cohort - which was divided into hardcore vegans, lacto-ovo vegetarians (who eat dairy), pesco vegetarians (who eat fish), semi-vegetarians (who eat some meat), and non-vegetarians - showed conclusively that those consuming a vegan diet were responsible for the lowest greenhouse gas (GHG) emissions, followed by the lacto-ovo vegetarians, then pesco-vegetarians and so on, with those on the non-vegetarian diet generating the largest environmental footprint, he said.

And for the first time*, he said, researchers also looked at the relative health outcomes of the five groups and saw a corresponding pattern, with the vegans having the lowest risk of chronic disease and the non-vegetarians the highest, providing compelling evidence that healthier diets are also more sustainable.

“It’s one of the first studies I am aware of that assesses the impact of reduced meat scenarios on GHG emissions and health outcomes in real world conditions.​

“Vegans’ GHG emissions ​[calculated using SimaPro7 life cycle assessment software​] were 41.7% lower than the non-vegetarians, lacto-ovo vegetarians’ emissions were 27.8% lower, pesco-vegetarians’ were 23.8% lower and semi-vegetarians were just under 20% lower.”​

Combined, the vegans and vegetarians generated 30% fewer GHG emissions than meat eaters, he told FoodNavigator-USA:

"The differences we have estimated are based on the AHS-2 non-vegetarian population as the reference or benchmark group. The consumption of animal products by this non-vegetarian population is less than that of the general population. This means that if we compared our vegetarian population against the average American diet, the reduction in greenhouse gas emissions would be even more dramatic."​

Meanwhile, the data also showed that the vegans and vegetarians had a lower risk of cardiovascular disease, cancer and diabetes, he said. (Click here​ to read more from the Congress on the benefits of plant-based diets on overall health... and click here​ to find out more about findings of a 'landmark' new study on plant-based diets and cardiovascular health.)

Dr Joan Sabaté: Producing 1kg of beef could take 13kg of grain​​

Dr Joan Sabaté: Sustainability is about health as well as environmental impact

In a passionate presentation in which he warned delegates that we are on a "collision course​" unless we change our eating patterns, Congress chair and professor in the Department of Nutrition at Loma Linda University, Dr Joan Sabaté said the energy input versus energy output of meat protein production compared with plant protein production was vast, adding: "Plant foods are eleven times more efficient than animal foods."​

He added: "The conversion of plant-based to animal foods is intrinsically inefficient... Meat production is generating low outputs of dietary energy and nutrients ​[compared with plant production]."

We have to drastically cut consumption of meat and dairy products​

With some caveats - eating some locally produced organic meat might be less energy intensive than, say, eating vast quantities of exotic fruit supplied via long-distance air transport - the take home message from the growing body of literature on this topic is that we “have to drastically cut consumption of meat and dairy products” ​to improve human health and reduce the environmental impact of food production, he said.

Now we know that plant-based diets are healthier and more sustainable​

Whether you look at water use, land use, GHG emissions or other measures such as energy efficiency ratios, no one disputes that it is more efficient to produce a kilo of pea or soy protein than a kilo of beef protein, he added.

And given that the supply of available farmland, water, fish and fossil fuels is finite, current eating patterns are clearly not sustainable.

“Just increasing agricultural productivity and tackling food waste are not enough. We have to radically change our eating patterns as well…. ​

"The nutritional paradigm has changed. Meat and dairy used to be considered essential in the diet in large proportions, but now we know that plant-based diets are healthier and more sustainable.”​

As for how to persuade consumers to change their diets, approaches that focus on how cutting down on meat and eating more plant-based foods could improve their health are much more likely to win people over than lecturing them about greenhouse gases or talking about the global food supply chain, which are not top of mind when you go grocery shopping, said Dr Harry Aiking, who is based in the Institute of Environmental Studies at VU University, Amsterdam.

“Stressing the health benefits of a vegetarian diet is likely to be more effective than talking about the planet.”​

Click here​ to read more from the Congress.

*The data presented by Dr Soret has not been published yet, but will form part of conference proceedings that will be published in the American Journal of Clinical Nutrition,​ he told FoodNavigator-USA. "We will be submitting the manuscript by the end of March. After that, the paper will go through scientific review. It will be several months before it appears published in ​AJCN."​

The GHG emission calculations were based on dietary intakes and did not include home energy use, car use etc etc.

Click here​ to read about a new study from France which suggests that diets of the highest nutritional quality are not however always​ the lowest in GHG emissions. Due to ease of transportation and storage, and relative lack of waste, the least healthy foods, like sweets and salted snacks, can be associated with some of the lowest emissions on an energy basis, said the study​.