A 'flexitarian' diet which includes one portion of meat a day has a lower carbon footprint than a vegetarian diet that includes dairy, according to a major new study.

The research by Johns Hopkins University (JHU) in Baltimore, America, could turn recent advice about diet and climate change on its head.

It modeled the environmental impact of all major diets across some 140 countries and concludes that those who switch to a vegetarian diet may be doing more harm than good.

By giving up meat and supplementing their intake with dairy products such as Halloumi cheese, yogurt and crème fraîche, vegetarians are only fractionally improving their carbon footprint.

The research shows they would be better cutting down on diary products, increasing their fruit and vegetable intake and eating meat once a day for protein and energy. They call this a "two thirds vegan" diet.

Here in the UK, the average healthy two-thirds vegan diet contributes the equivalent of 762.7 kg of Carbon Dioxide emissions (CO2e) per-person, compared with 1,265.2 kg for a vegetarian diet that includes dairy.

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Dr Keeve Nachman, one of the paper’s authors, told The Telegraph: "Dietary shifts don’t have to be as draconian as many people think to have a meaningful impact on the environment.

"Our study found that in the UK, switching to a vegetarian diet that includes eggs and dairy is actually less helpful for reducing greenhouse gas emissions than a diet that includes meat, dairy and eggs for one of three meals, and is exclusively plant-based for the other two meals."

Academics have been warning for some time of the climate impact of diets high in meat.

The new JHU research confirms this and finds that cattle, sheep and goat meat are the most greenhouse gas intensive foods, but says that dairy is not far behind.

For the UK, average food consumption contributes 1,968.1 kg of CO2e per-person, the study finds. Dairy makes up almost a quarter these emissions, jumping to two-thirds (845.6 kg) for vegetarians.

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According to Dr Nachman, switching to a healthy vegetarian diet would include dairy and eggs at rate slightly above the norm to offset the loss of meat. Conversely, the two-thirds vegan diet in a country like the UK is a considerable reduction in some of the most climate intensive foods.

In comparison to switching over to dairy and eggs, it is a sizeable reduction in footprint.

The study indicates that meat production and consumption cannot be sustained at current levels. It agrees with other research that it must be brought down globally if climate change is to be brought under control.

“Certain forms of beef production can significantly reduce our capacity for carbon sequestration. In particular, production that involves deforestation for feed production and grazing land has serious implications for our climate,” said Dr Nachman.

“Including beef in our diets at current rates would have grave consequences for the environment.”

Many low and middle income countries have been shifting towards a more western meat-based diet, with experts warning that this will have serious environmental consequences.

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In a scenario where all 140 countries adopted the consumption patterns of high-income countries, per-person greenhouse gas emissions would increase by 135 per cent on average, according to the JHU research.

On the other hand, a global shift to a strictly vegan diet would reduce diet-related greenhouse gas emissions by an average of 70 per cent.

A vegan diet supplemented with "low-food chain animals" such as insects would have similar benefits, while also providing a better source of protein and vitamins.

Insect-based diets have struggled to find consumer acceptance, especially here in the UK, but Dr Nachman is hopeful that attitudes may change.

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“There are many parts of the world where eating insects isn’t an outlandish idea. Based on our data, there may be great value in exploring ways to normalize this in other parts of the world.”

For the moment, however, the study's authors suggest that adopting a flexitarian or two thirds vegan diet, where protein is provided not by insects but meat, is a good place to start.

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