8 billion people on earth, takes 6 months to raise a cow for food. If each person wants ~50 lbs of beef each year that's about 400 million cows assuming a perfect system. That'll require 800 million acres just so people can eat cows. Not to mention the byproducts.

Sustainable livestock sounds great. But it won't scale far enough to meet even the current US demand, at least not if grown domestically. So maybe just subjugate a bunch of other countries, and ensure they do it sustainably! Can't be clear cutting rainforests we might need to breath or anything.

For some perspective, 800 million acres is about 1.25 million square miles, or approximately 1/3 of the land area of the forty eight contiguous states. 900 million acres is approximately the amount of agricultural land in the US. If this estimate were true and would provide meat for the entire world, I think we'd be okay spacewise.

That doesn't account for the byproducts, assumes ideal efficiency, and puts a huge squeeze on other agriculture. Then there are resources consumed by transportation, refrigeration, spoilage, etc.

As we search out the threshold of unsustainable living maybe we could tap the breaks a bit first? Earth is a nearly closed system we must all share, and cows are a terribly inefficient way to produce protein and calories.

Read about blue region people who eats much less meat, in most Blue Zones diets people ate small amounts of pork, chicken, or lamb. https://extension.psu.edu/longevity-tips-from-the-blue-zones

avg american men eats more than 100gm protein perday, CDC recommends 46-56. As you asked, now are you going to follow that? https://www.bluezones.com/2020/07/blue-zones-diet-food-secre...

No the CDC recommendations are based on junk science and fail to account for the latest medical research. Sure you can survive on that much protein, but it's not sufficient for optimal performance. Look at what winning athletes usually eat.

https://peterattiamd.com/category/nutritional-biochemistry/p...

Not everyone can be an athlete and few people exercise enough to justify the same calorie and protein budgets as athletes.

Everyone who isn't severely physically disabled can (and should) be an athlete if they want to have a long healthspan. High protein intake is essential to prevent sarcopenia as we age and our digestive systems become less effective at extracting those nutrients. Please read though the reference I provided above instead of spreading misinformation.

Can you link to an original source? I couldn't find one following that spammy blog.

From what I could find sarcopenia's exact causes aren't fully understood yet.

Regardless of the correct quantities protein does not need to come from animal sources. And if we want to live with less suffering and environmental destruction we'll need to reduce reliance on animal protein.