255 grams per week. That’s the short answer to how much meat you can eat without harming the planet. And that only applies to poultry and pork.

Beef cannot be eaten in meaningful quantities without exceeding planetary boundaries, according to a scientific article published by a group of DTU researchers in the journal Nature Food. So says Caroline H. Gebara, postdoc at DTU Sustain and lead author of the study.

“Our calculations show that even moderate amounts of red meat in one’s diet are incompatible with what the planet can regenerate of resources based on the environmental factors we looked at in the study. However, there are many other diets – including ones with meat – that are both healthy and sustainable,” she says.

How much is ‘less’?

The researchers’ first goal was to investigate whether it is even possible to fulfil the nutritional needs of the entire global population without exceeding planetary boundaries. According to the calculations, it is possible. But it will require a change in our food consumption on both a global and individual level, says Caroline H. Gebara.

“The global shift requires political action at the top level, while the individual shift will be much easier if we have better guidance and frameworks that support sustainable choices,” she says.

The next goal of the research was therefore to come up with concrete figures for how much of different foods you can eat without consuming more of the earth’s resources than it can regenerate, says Caroline H. Gebara.

“Most people now realise that we should eat less meat for both environmental and health reasons. But it’s hard to relate to how much ‘less’ is and whether it really makes a difference in the big picture. Therefore, based on the planetary boundaries, we have calculated a concrete figure – 255 grams of poultry or pork per week – which you can actually visualise and consider when you are standing in the supermarket,” she says.

In Danish supermarkets, a pack of two chicken breast fillets typically weighs 280 grams which is slightly over the limit of what one person can eat in a week without exceeding the planetary boundaries.

Not either-or

The research team’s calculations take into account a number of environmental factors such as CO₂ emissions, the consumption of water and land use, as well as the health impact of a particular diet. In total, they have examined more than 100,000 variations of 11 types of diets and calculated their respective environmental and health effects.

And the calculations clearly show that a diet with even moderate amounts of red meat – beef or lamb, for example – exceeds planetary limits.

A pescetarian, vegetarian or vegan diet, on the other hand, is likely to stay within the limits of what the planet can support. But this also depends largely on the specific products included in the diets.

In addition, different combinations of diets, such as vegetarian but with dairy or eggs, can also be sustainable.

And that’s exactly what Caroline H. Gebara hopes that the study will help more people realise: That a sustainable diet can take many different forms.

“For example, our calculations show that it’s possible to eat cheese if that is important to you, while at the same time having a healthy and climate-friendly diet. The same is true for eggs, fish and white meat, but the premise is of course that the rest of your diet is then relatively healthy and sustainable. But it doesn’t have to be either-or.”

You can read the full study in Nature Food.

According to a new study co-authored by a Tulane University researcher and published in the journal Nature Food, making simple substitutions like switching from beef to chicken or drinking plant-based milk instead of cow’s milk could reduce the average American’s carbon footprint from food by 35%, while also boosting diet quality by between 4-10%, according to the study.

These findings highlight the potential of a “small changes” approach that researchers believe could encourage more consumers to adopt climate-friendly eating habits. Food production accounts for 25-33% of the nation’s greenhouse gas emissions with beef production being a primary contributor.

“This study shows that cutting dietary carbon emissions is accessible and doesn’t have to be a whole lifestyle change,” said Diego Rose, senior author and nutrition program director at Tulane University School of Public Health and Tropical Medicine. “It can be as simple as ordering a chicken burrito instead of a beef burrito when you go out to eat. When you’re at the grocery store, move your hand one foot over to grab soy or almond milk instead of cow’s milk. That one small change can have a significant impact.”

The study, which analyzed diet data from over 7,700 Americans, identified commonly eaten foods with the highest climate impact and simulated replacing them with nutritionally similar, lower-emission options.

“For us, substitutes included swapping a beef burger for a turkey burger, not replacing your steak with a tofu hotdog,” said Anna Grummon, lead author and assistant professor of pediatrics and health policy at Stanford University. “We looked for substitutes that were as similar as possible.”

The largest projected reductions in emissions were seen in mixed dishes: burritos, pastas and similar popular dishes where it’s easy to substitute a lower-impact protein instead of beef.

The study expanded on past research by including dietary data for children. Whereas it may be more effective for an adult to focus on protein swaps, Grummon said switching children to plant-based milk can have a “meaningful impact on the carbon footprint” and help start positive habits earlier.

Identifying healthy alternatives to high-carbon foods was not the intent of the study. And yet, swapping to lower carbon foods showed “sizable improvements in how healthy the diets were.”

While these substitutes are not intended as a cure-all for climate objectives or personal health goals, they are evidence that small changes can have a large impact.

“There is overlap between sustainable diets and healthy diets,” Grummon said. “Our study shows that changing just one ingredient, making one swap, can be a win-win, resulting in meaningful changes in both climate outcomes and how healthy our diets are.”

Other co-authors of the study included Cristina Lee and Thomas Robinson of Stanford University and Eric Rimm of Harvard University.