A sustainable diet leaves room for two chicken breasts a week

We should eat less meat and more legumes, campaigns and dietary advice tell us. But how much is "less"? Researchers from DTU have an answer.

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.

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Facts

What are the planetary boundaries?

The nine planetary boundaries are scientifically based estimates of how much human impact the planet itself can compensate for.

For example, when humanity collectively consumes more freshwater than the planet is able to produce, we have breached the planetary boundary for freshwater consumption.

The nine planetary boundaries are:

1. Climate change

2. Loss of biodiversity

3. Freshwater use

4. Land area use

5. Emissions of ozone-depleting chemicals

6. Pollution with man-made substances

7. Release of aerosols into the atmosphere

8. Emissions of nitrogen and phosphorus

9. Loss of calcium carbonate in the ocean

Of the nine planetary boundaries, six have already been breached, according to a 2023 study by the Stockholm Resilience Centre, which first defined the boundaries in 2009. Only numbers five, seven and nine are still at a level that the planet itself is believed to be able to compensate for.