Danish research from March 2025:

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.

• https://www.dtu.dk/english/newsarchive/2025/04/a-sustainable-diet-leaves-room-for-two-chicken-breasts-a-week

American study from 2016:

Abstract
[...]
Transitioning toward more plant-based diets that are in line with standard dietary guidelines could reduce global mortality by 6–10% and food-related greenhouse gas emissions by 29–70% compared with a reference scenario in 2050.

• https://www.pnas.org/doi/abs/10.1073/pnas.1523119113
• https://www.researchgate.net/publication/299342863_Analysis_and_valuation_of_the_health_and_climate_change_cobenefits_of_dietary_change

American study from 2022:

Based on the model, published in the open-access journal PLoS Climate, phasing out animal agriculture over the next 15 years would have the same effect as a 68 percent reduction of carbon dioxide emissions through the year 2100.
This would provide 52 percent of the net emission reductions necessary to limit global warming to 2 degrees Celsius above preindustrial levels, which scientists say is the minimum threshold required to avert disastrous climate change.

• https://sustainability.stanford.edu/news/could-going-vegan-help-reduce-greenhouse-gas-emissions
  The study: https://journals.plos.org/climate/article?id=10.1371%2Fjournal.pclm.0000010

For the most part, not only does vegansim have the biggest positive impact on the environment that can be made with a personal choice, the animal products industries are like the third biggest contributor to climate change after energy (coal, oil, gas, etc) and manufacturing. Plus, as most farm land in the world is used for animal feed, it would free up land for reforestation.

P.s When talking about GHG emissions, it's a really bad idea to use % of total emissions as an indicator of impact. Livestock produce plenty of methane, which is roughly 84 times more impactful than carbon dioxide on the short term (20ish years) but carbon dioxide is more impactful over the long term (centuries) as it does not break down as quickly.

Just upvoting because it's a good question. I often find myself wondering just how much "X" can I consume before I should reign it in for the betterment of the planet. I'd like to be able to say I left earth better than I found it. Mainly thinking about things like gasoline, but food should certainly be on that list as well. Consuming zero of everything isn't a solution, but figuring out how much is okay - yeah, that's tough.

Don't lose sleep over individual contributions. It's the corporations that need to change behaviour. Put your energy into fighting them.

Not an answer, and I won’t get a lot of upvotes for saying this, but if your plan for saving the world is for people to change their behavior en masse, you’ve already lost. And we need population-level change in order to have a meaningful impact.

The way we get people off meat is by making the alternatives more (or equally) tasty, convenient, familiar, and affordable. The day we do that, the war is won. There will be some stragglers (of the “beef! murica!” variety) but not many.

We’ve made inroads. Indian food is delicious, way more popular in the West than when I was growing up, and vegetarian-inclined. Vegetarian burgers are more popular and varied than ever. New meat substitutes are being invented all the time. People are interested, but there’s not a well-lit path to vegetarianism for working-class folks just yet.

If you want to eat less meat, do it. But also, find some good meatless recipes and cook them for/with your friends. If they add those to their rotation and pass them along, that’s the kind of thing that can build toward change.

Animal agriculture only produces 5.8% of greenhouse gasses[0], so even if everyone stopped eating meat tomorrow the effect would be less than 5.8% (not all animal agriculture is for meat).

[0] https://ourworldindata.org/ghg-emissions-by-sector

There are also strong movements to healthier eating and a good strategy might be to build on that.

While it’s always dangerous to generalize from personal experience, I know far more people who have reduced their consumption of red meat, or even overall meat, For health reasons over climate reasons

Google says livestock production creates 11-20% of global human co2 emissions. Even If we could make that disappear, it’s not enough

Meanwhile energy production is 73% so it’s critical to focus there

Realistically there is to switch to zero for any category of emissions so the only right answer is to cut as many as possible as much as possible

On an industrial scale you basically have to ban meat to protect the environment. There simply can't be 8+ billion meat eaters.

Maybe bug meat could be environmentally friendly, but at that point why not just eat plants?