dairy cow chewing the cud

Should you become a vegan to save the planet?

We could all just eat plants because health and vitality are a kale salad away. But there is no simple switch for such a drastic change in global land use…

Does becoming a vegan help save the planet?

Well, there is scientific logic in veganism for saving the planet. Not that the planet needs saving but that is for another post. The reason is all to do with nature’s struggle against the second law of thermodynamics.

All organisms pay an energetic cost of living.

To defy entropy—the gradual decline into disorder—and beat the second law of thermodynamics that entropy always increases with time, all organisms need to use energy.

Plants generate energy through photosynthesis, whereas animals, including humans, respire the energy plants capture. Just to maintain bodily function, a human male needs to consume 1600 to 1800 kcal/day of energy in food.

The conversion of energy from food is not that efficient. Aerobic respiration converts about 40% of the available energy of glucose with the rest lost as heat so animals get to use around 40% of the energy that the plants have stored.

Cows in a feedlot
Photo by Eric Herni on Unsplash

In January 2018, there were an estimated 32 million beef cows in the US.

Animals eat a lot. 

At peak lactation, a dairy cow needs to eat around 16 kg dry mass of grass per day, whilst in feedlots, beef cattle consume 6 kg of feed for every kilogram in weight gain.  

Here we have the ‘save the planet’ logic of veganism.

It is more efficient in energy terms for humans to cut out the cow and eat the plants directly.

Giving up the energy lost in trophic transfers presents an energy-saving from going vegan.

The situation for nutrients is slightly different. 

Humans can obtain all their essential nutrients and proteins from plants, but the concentrations of the key nutrients are lower in plants than in animal protein. Nutrient load is not the same for each plant type either. So to obtain a balanced nutrient intake, humans need to eat a combination of seeds, grains, pulses, fruits and vegetables. 

We need more plants and a wider variety than if meat was in the diet.

Meat is a protein and nutrient bomb that, whilst not obligate (essential) in the human diet, has made the difference in where humans can persist and thrive over the millennia. Indeed in cold climates where the body has to work hard to stay warm, people often crave animal fats.

The argument that we should be vegetarians is only a moral one. Our biology permits meat as a nutrient and energy source, and our success is because we took the efficiency opportunity that meat provides. 

All this explains why humans eat meat and are likely to keep eating it. 

But here is the global challenge…

More than 80% of the world’s farmland is used to raise and feed cattle and other livestock, but these provide only 18% of all calories consumed.

It is easy to look at these numbers and see the solution — most of us give up meat.

Going vegan would release land to grow all the extra plant food that we need to feed everyone, plus meat only provides a fifth of the calories anyway.

However, calories are not nutrients. In other words, we eat meat because it provides us with much more than calories. But this nutrient demand isn’t even the main problem with the ‘plenty of land’ logic.

There isn’t plenty of land at all. 

Infographic of the proportion of the global land area used for agriculture

Globally, agricultural land area is approximately five billion hectares or 38% of the global land surface. About a quarter of this is used as cropland. The vast majority of agricultural land is for grazing and most of that is used for extensive grazing on rangeland, which is natural vegetation.

Only 23% of agricultural land is used to grow crops because it is hard to grow crops anywhere else. A crop needs good soil, enough rainfall (but not too much), warmth (but not too hot), and the absence of extreme weather. Where these conditions hold we grow crops. Rangeland is used for livestock because that is the most efficient use of the land.

Some suitable arable land grows feed for livestock, which could be shifted to crops for human consumption if humans stopped eating meat. 

Arable land is also used to grow biomass fuel. For example, the US produced over 13.9 billion gallons of ethanol in 2020 mostly from corn and overall biofuel consumption totalled 1.09 million barrels per day and accounted for 7.3% of total motor gasoline, distillate, and jet fuel consumption.

Aside from this competition for biomass from fuel use and fixing some issues with supply chain losses and food waste, most research estimates suggest that the one billion hectares of available cropland are enough to feed everyone grains, greens, and seeds.

If we could increase the crop production from one billion hectares to cover the deficits—18% of calorie and 37% of nutrient supply that currently come from livestock—we could all go vegan and leave the rangeland alone.

Vegan humanity would certainly make it easier to achieve the rewilding target of 30% needed to keep us within planetary limits.

So far the logic for not eating meat stacks up pretty well. 

Veganism (or vegetarianism) is within our biology, would provide us with enough energy and nutrients, and could be achieved with minor modifications to land use. Land rewilded, lower carbon emissions and less water use would reduce the pressure on planetary boundaries and improve ecosystem services with flow-on effects to other human values such as biodiversity preservation.

All good until the but…

Large bowl of steamed vegetables
Photo by Hermes Rivera on Unsplash

In 2021 roughly 79 million people were vegans, roughly 1% of the global population.

Hidden consequences of a meatless diet

1. Precarious production

Humanity has to meet the 22 trillion calories a day challenge.  These are the calories needed for everyone to defy entropy with enough energy left over to go about our everyday business.

It’s a lot of energy.

Fail to meet this demand and people go hungry, especially the poor. Fail often and we can add regional famine to pandemics and financial crises as global economic disruptors. Fail too often and everything falls over.

Soil needs help in supporting plants when the nutrient-dense parts of the plants (grains, seeds, tubers) are harvested and leave the farm with every crop. 

If we choose to meet this food energy demand only with plants then we have to grow crops with energy subsidies—fertilisers, machinery, pesticides. 

This has happened since the late 1800s with the invention of farm machinery, especially since the early 1900s when internal combustion engines replaced horses on farms in Europe and the US. Thanks to what Nate Hagens calls our energy slaves, food production has grown into more and more people. But to feed them all plants means intensive agriculture must persist for a long time.

The evidence is that soils degrade under continuous crop production and might not be able to accommodate the levels of energy and nutrient subsidy needed to maintain yields even if we find an alternative to oil to provide the subsidy.

Feeding everyone plants pushes humanity into a precarious food security position that relies on inputs that may not work and inputs we might not have.

2. Nutrient recycling

Before the industrialisation of agriculture most farms were mixed. They produced a few crops, some hay, vegetables and fruits in kitchen gardens and tied it all together with a combination of animals mixed and matched from cattle, sheep, pigs, goats, poultry, and the occasional exotic.

Most subsistence farming systems combine plants and animal production and there are 500 million of smallholder farms worldwide that feed more than 2 billion people. Around 80 per cent of the food consumed in Asia and sub-Saharan Africa comes from smallholders.

Livestock were an invaluable source of protein from meat, milk and eggs, but they also provided manure. Feeding the animals plants was a net benefit because their grazing, foraging and defecating was invaluable in returning nitrogen and organic matter back into the soil.

Plants fixing energy consumed by animals with waste recycled by microbes and soil organisms is an accurate summary of nature. A version of this energy and nutrient transfer happens everywhere on the planet.

Livestock help farmers mimic nature.

When farmers only produce plants their systems of production is decoupled from these natural processes of energy transfer and they have to replace the transfers with something else, typically tillage and fertilisers. 

Nature has persisted on earth for 3.5 billion years and in a form that has supported mammals for over 200 million years and humanity for 300,000 years. Intensive agriculture has been around for a little over 100 years. Its longevity is unknown.

3. Human nature

People have always eaten animal products. 

Meat, dairy, eggs, blood, offal are all entrenched in local traditions and diets in almost every culture and country on earth. As we have seen in the staggering growth of pork consumption in China, people consume more animal protein when wealth increases. Only in the last 75 years have cereals, sugar, and seed oils come to dominate the western diet.

 Most people like animals.

 In just about every culture humans have created, animals are ever-present. Livestock are more than just food.They can provide materials, transport, security, be a form of currency, a companion and beloved family member. 

The 2017-2018 U.S. Pet Ownership & Demographics Sourcebook shows that American households owned 76 million dogs, 58 million cats, 8 million birds and 2 million horses. Each dog cost their owners an average of $250 a year in veterinary care.

The meaning animals have combined with the land use ideas we discussed earlier brings another challenge for the logic of only eating plants.

In practice, land use is already set to accommodate animals. It will take a monumental effort of will to unpack all the ownership, traditions, and land suitability issues to remove animal production from human systems. 

Then there is the obvious human nature issue of plants only eating—the psychology of changing diets.

Joint of beef ready for the oven
Photo by Wesual Click on Unsplash

In 2011 the global John Doe consumed 173 grams of meat per day.

What sustainably FED suggests

If a vegan or vegetarian diet is attractive to you, go for it. 

Some people will gain significant dietary and psychological benefits from not eating meat or animal products—but stay clear of inflammatory grains and sugars.

The planet does not need saving, she will persist with or without humans. But what about the premise that becoming a vegan will somehow help?

Will a vegan diet save humanity? 


Planetary limits cannot support 7.8 billion people growing to 10-11 billion by 2050 on plants alone because that would mean energy and nutrient subsidies into agricultural production systems that will make them precarious, fragile and likely to collapse.

Even if we knew how to replace oil and gas—perhaps fusion power that was ubiquitous enough to fix nitrogen on the required scale and mine all the trace nutrients—the required intensification would further separate food from nature. 

Soil as a medium for plant growth would fail and whatever we found as a substitute would need to scale to 22 trillion calories a day. 

Production systems must become circular for energy and nutrients, recycling as much of both as possible. The best way to do this is through ecology, which means animals—the big animals that we husband and the small animals that enliven the soil. 

The nutrient density of animals means we cannot ignore their contribution to food security either.

Ironically veganism would mean more agricultural intensification and send us further from nature than we are already.

Hero image modified from photo by Andy Kelly on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

1 comment

  • This premise that veganism “would mean more agricultural intensification” is completely false, countless studies show otherwise. Most of starving people live in countries where food is fed to animals who are eaten by western countries. If you want to learn about, you should read “Regenesis” of George Monbiot.

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