tape measure of diet

What is a sustainable diet?

A sustainable diet is the D in sustainably FED. It is intimately connected to food production and the ecological engine we rely on to meet food demand. Here we explain why understanding diet is essential to feeding everyone well

If we said sustainable diet, you might imagine being on a diet you could stick to by some miracle of self-control until the desired weight loss target was met.

And sure, that is one legitimate way of thinking about it. 

However, the word ‘diet’ has many meanings. It can be a noun, adjective and even a verb. It is what we eat and choose to eat, and we can even be on a diet. 

Because of these multiple meanings, sustainably FED chose diet as the third of our three pillars for feeding everyone well. Food for everyone can only happen with a thorough understanding of diet.

Sustainable diet is the D in sustainably FED. 

We need to know what we eat, why we eat these foods and the personal and global consequences for the collective human diet.

Diet is individual, a family thing, a societal descriptor and even a national and global concept. 

Let’s take a look at each of the levels.

You are what you eat.

In 1826, a remarkably prescient French lawyer, Anthelme Brillat-Savarin, wrote, ‘Dis-moi ce que tu manges, je te dirai ce que tu es’ that translates as ‘Tell me what you eat and I will tell you what you are’. It is unlikely Monsieur Brillat-Savarin knew just how accurate he was. 

Modern nutritional and health science tells us that what we eat combined with the bacteria in our gut significantly affects our physiology, health, well-being, mental health and longevity.

Eat well and live a longer, healthier, more active life with a lower risk of non-communicable diseases from heart disease to cancers.

Eat the wrong foods out of balance or in bad combinations, and your nutritional health can fall off a cliff and bring on many unpleasant consequences.  

Most of us know this truth at some level. 

Wake up from a night on the town that took in several beers and a kebab around 2 am, and you know that what went in your mouth did horrible things to your body. Your head is pounding, your stomach is huge, and you barely have the energy to stand. Then you fart.

Many of us are familiar with these symptoms; perhaps only a few know what happened.

At first, the liver kicked in to process the alcohol that arrived in the first couple of beers that left the intestines in a hurry. The liver deals with alcohol as though it were sugar; it turns it into fat.

The kebab arrived when the digestive system was already overloaded. It contained animal protein, saturated fats, a variety of novel chemicals and wheat. Your body was familiar with the animal products, given that your African ancestors had been eating similar foods from the beginning. Wheat, on the other hand, is a new food to the human diet, and although you have eaten many kebabs, crusty loaves and meat pies in the past, your digestive system is not designed to process such volumes of processed starch.

On your big night out, you overloaded your digestive system with novel foods at levels to make them poisonous.

Nonetheless, you survived. And this is a truly remarkable feature of human physiology—it can tolerate a lot of abuse and still recover. 

So if alcohol, sugar, wheat, novel chemicals, trans-fats and several other likely suspects are wrong, what is a sustainable diet for an individual?

First, we have to review some ancient history.

Dramatic changes to human diets 

Long before agriculture, humans lived in small groups that wandered across the landscape, constantly searching for food. 

The popular image is of mighty hunters cooperating to bring down woolly mammoths when more often, everyone was grubbing around to forage for roots, tubers, insects, berries, and the occasional tree in fruit. 

But our ancestors did have advantages.

Control of fire meant we could cook meat that would otherwise be rancid, allowing our ancestors to scavenge from stronger predators. Many groups lived close to water, where foraging could include fish, shellfish, crustaceans, and even seaweed. They also had a large brain and an acid gut.

Early hominids and their Great Ape descendants had a large gut—gorillas, chimps, bonobos and orangutans still do. They primarily eat plants that need a large gut to digest through fermentation. Homo sapiens went for the large brain and gave away the large gut because energy constraints meant we couldn’t have both. 

Big brains were handy for controlling fire, especially cooking, tool use, communication, and cooperation, including hunting and scavenging. And an acid stomach is an advantage if the meat you find is a little fruity. 

Overall the big brain allowed the diet to become meat over plants, especially cooked meat, and that had a significant advantage—meat and animal fats present a much higher nutritional and energy return on effort than plants.

Homo sapiens retained the ability to eat plants, but we became true omnivores with the physiology to persist on animal protein and fats.

Saving food for the drought 

Early humans ate what they could whenever it was available. 

Although they probably figured out a range of drying and fermenting preparations, they had minimal ability to store food. Fruits and meat easily rotted, and there are only so many ostrich eggs that can be carried from place to place.

But they had one significant physiological advantage.

What is true about the modern interpretation of the paleo diet is that most of the energy from food comes from the metabolism of proteins and fats. There is a reason carbohydrates are a non-essential macro-nutrient.

But we can store them as fat in the buttocks and around the stomach when we eat them.

Before we learned to use animals as walking larders, we ate voraciously when there was abundance and stored the excess energy in our bodies. Body fat has a horrid reputation in modern times, but it is likely one of the key adaptations that allowed us to become modern. 

It meant we could carry fuel for hard times. 

Omnivorous variety

Back in the days before agriculture, no food was ever regularly abundant. 

The occasional kudu or fruiting marula tree provided a feast,  but these were infrequent events. When an animal was captured, people prized the liver, fat and organs over the lean meat. Our energy food was fat.

However, the actual paleo diet was not protein-rich raw meat with a side of intestines but a combination of food types, primarily plants and insects. Early humans did not have an abundance of carbohydrates—little or no sugar, few grains and just the occasional starchy vegetable.

The key feature of our evolutionary diet, the food our ancestors ate, was variety—humans had a diversity of diet.

Wilma Flintstone, who lived her whole life within the valley she was born and raised, might have eaten fifty different foods before she died. Meanwhile, her distant cousin in the next valley, who she had never met, ate 50 types too, and most, but not all, were the same. 

Another woman who belonged to a tribe that had moved north a hundred generations earlier was eating walrus, seal and salmon along with some berries gathered in the autumn. Wilma had no idea there was such a thing as the ocean, let alone a walrus.

Homo sapiens didn’t just eat a wide variety of foods as individuals. As a species, we ate almost everything everywhere we went. 

And we went everywhere.

A great migration

Anthropologists and evolutionary biologists estimate that this broad pattern of foraging, hunting and scavenging for a wide range of foods persisted for nearly 300,000 years, the estimated ‘lifetime’ of Homo sapiens—plenty of opportunity to learn many skills and knowledge.

Just to remind ourselves that this is a long time, recorded history at 5,000 years is just 1.6% of the time we have been recognised as a species. 

The first 230,000 years or so were spent in Africa, and then enterprising humans began a trek across the rest of the planet, reaching all but the remote islands before the invention of agriculture. 

This was a dramatic expansion in both scale and speed. Some estimates have the journey across North and South America took just 2,000 years. During this great migration, humans encountered and thrived in various habitats, from the Middle East’s hot deserts to the Artic tundra. 

map of the world showing where and when Homo sapiens moved around the planet in search of their sustainable diet

By User:Dbachmann – Own work;Map: File:World map blank shorelines.svg (the shoreline map is {{PD-USGov-USGS}}, derived from a mercator svg map posted in 2005, extracted from an original file released by pubs.usgs.gov), CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=68921860

Such an expansion could only have happened if humans found edible food in each new habitat they encountered. They must have been very good at finding food, learning what to eat and avoid, and, perhaps, copying from their Hominid cousins, the Neanderthals in Eurasia, Homo floresiensis in Indonesia and the ‘Denisovans’ in Siberia.

By the time Homo sapiens reached Patagonia around 14,000 years ago, the range of foods the species ate was vast.

Then there was a change.


About 12,000 years ago, multiple groups of humans learnt how to grow crops in an area that includes modern-day Iraq, Jordan, Syria, Israel, Palestine, southeastern Turkey and western Iran. Other humans in China began cultivating millet around 11,000 years ago, whilst independently, humans developed a range of crops in South and North America around 9,000 years ago.

These multiple origins of crops were mainly grains.

For the first time in our evolutionary history, humans had a significant new energy source—carbohydrates.

Carbohydrates were a boon for society, culture and population development but could have been better for nutrition. Human digestion and gut biota expect a variety of foods, not the predominance of a single source. We return to this shift in diet often in our sustainable diet posts.

Some anthropologists suggest that nutritional health declined with early agriculture, but the net energy gains and the benefits of organised societies saw a net increase in population. Jared Diamond describes that some cultures collapsed, but the human population increased. Not only were humans everywhere, but they were also numerous in some places.

Our physiology was flexible enough to persist and thrive on a food energy surplus despite poorer nutrition.

Then just 100 years ago, everything changed again. 

A small illustration captures the moment.  

Energy source or energy sink

Charles W. Hart and Charles H. Parr built the first successful American tractor with a gasoline engine in Charles City, Iowa. In 1903, the firm built 15 tractors designed to haul a trailer or machinery with high tractive effort (or torque) at slow speeds. 

A little over a decade later, Henry Ford introduced the Fordson, a wildly popular mass-produced tractor dispensed with a frame, using the strength of the engine block to hold the machine together. Fordsters were built in the U.S., Ireland, England and Russia, and by 1923 gasoline-powered internal combustion engines had become the norm.

It is tempting to think that the invention of agriculture was pivotal in human history. It was a big deal that changed many things but wasn’t the most significant.

The actual pivot came when humans made agriculture an energy sink.

Tractors meant clearing vegetation, ploughing fields, and spreading fertilisers made in factories was possible. Fields got larger, and whilst yields were still modest, the volume of crops increased dramatically—there was more food energy available. But it took a lot of energy from fossil fuels via machines to make the energy source for humans.

Agriculture became a sink rather than a source of energy even though the volume of food production increased dramatically.

Most of the boon in food energy came from grains, sugar and the industrial production of livestock products.

Soon the human diet had changed again. People were consuming more wheat, sugar, and animal products as bread, pies, and pastries.

And then there was a war.

A consequence of war

The Second World War was a global disaster. It brought genocide, the blanket bombing of cities, and the first use of nuclear weapons. More than 100 million personnel from 30 countries created the deadliest conflict in human history, with over 70 million fatalities, the majority civilian.  

This six-year global conflict had many consequences that rearranged geo-politics and the global economy. One of the more long-lasting was the leap in industrial capacity in North America and Europe. The construction and repurposing of factories and systems to mass produce weapons and munitions showed what could be done—US industrial production doubled in size in four years and delivered 297,000 aircraft, 193,000 artillery pieces, 86,000 tanks and two million army trucks—and it was staggering. 

Soon after the war, the same factories and their newly minted labour force were producing all sorts of goods for mass consumption.

Maddison Avenue was invented to persuade people to buy this plethora of options, and before long, people in mature economies were eating processed foods. Instead of homemade apple pie, it was a mass-produced option from the freezer aisle. Today a single ConAgra factory that produces Marie Callender’s apple pies churns out 210,000 pies per day made with vegetable shortening.

New tractors and farm machinery went out to the fields. Factories refitted for pies, pastry and colourful packaging produced goods loaded onto new trucks to take these processed foods to all corners.

Diet changed again.

What Westerners eat today is built around grains, sugar, seed oils and animal products, all heavily processed into an unfathomable number of commodities. These are the products of the factories and farms fuelled by fossil energy—collectively a massive energy sink.

The modern Western diet might be alien to human physiology, ultra-processed, overabundant and frequently toxic, but it is also highly profitable. It makes bucketloads of money.

What does a market do when there is money to be made? It makes money and extends that market as far and wide as possible. A Westernised diet of ultra-processed grains, oils and sugar is steadily overtaking traditional diets worldwide.

In 2021, 56 million tonnes of wheat were imported into Africa, 7% of global production, to help feed 1.2 billion people. Only these people don’t traditionally eat wheat—just 9 million tonnes were grown on the continent in 2021—Africans are familiar with leafy greens, root vegetables, mashed tubers and beans, and many different grain crops, especially millet, sorghum and maise.

Apologies for the lengthy digression into anthropology, ancient and modern history, but the scene is now set to answer the question in our title…

two women sharing a meal in a restaurant
Photo by Farhad Ibrahimzade on Unsplash

What is a sustainable diet for human health? 

Not what we eat today.

A sustainable diet should:

  • Promote long-term metabolic health by delivering optimal nutrition and helping prevent avoidable diseases like type-2 diabetes.
  • Fit with our digestive system and metabolism that has evolved for 93% of our 300,000 years as a species based on what our ancestors could find in nature.
  • Deliver between 2,000 and 3,000 kilocalories of energy subject to the amount of physical activity required, has a good balance of macronutrients and the full complement of micronutrients.
  • Match the owner’s gut biota and feed those microorganisms with enough fibre.
  • Contain few, if any, toxins and undesirable microorganisms
  • Contain next to no processed food, little sugar, modest amounts of grains, some animal proteins and plenty of colours as an indicator of variety
  • Be tasty, look great and be consistent with cultural norms and practices.

Suppose these features are present in the sustainable diet. In that case, a person can optimise their metabolic health and potentially reduce the incidence of diet-related diseases—heart disease, high blood pressure, type 2 diabetes, osteoporosis, tooth decay, gout, kidney disease, stroke—and certain cancers.

A sustainable diet can be mostly plant-based but will usually include animal protein. It could be delivered around protein and fat as the primary energy source. Human metabolism is okay with that.

A healthy diet is what we used to eat because we are designed to eat it. Very few people in the global north eat like this.

Most modern humans eat an unsustainable diet built around grains, sugar and seed oils delivered as processed commodities. This is slowly killing us with sweet and savory kindness. 

If what we used to eat is a healthy diet and what we used to eat was variety, often, and only occasionally in abundance, how does this translate to a human population that has increased from 2.4 to 8 billion people since the end of World War 2?

Sustainable diet for 8 billion people

We estimate that feeding everyone is a daily 22 trillion kilocalorie challenge for energy alone. 

Feeding everyone well means that the calories must arrive in food that also supplies adequate nutrition without damaging metabolic health.

Twenty-two trillion kilocalories might be doable with grains, sugar and seed oils but feed foods with these primary ingredients to everyone, and sooner or later, they get sick—excess carbohydrates in ultra-processed products might sell well. Still, they do not make a sustainable diet.

Instead, there has to be variety, including animal products, fruits and vegetables.  

8,000 an hour

Daily production and delivery of 22 trillion kilocalories worth of food to 8 billion people is mind-boggling. That it happens, more or less well, is a miracle of human ingenuity, cooperation and enterprise. 

And all the while, the challenge gets more complex.

In the time it takes you to read this post, 1,600 people will be added to the people still alive. That is enough to fill the places in three average-sized public schools in the US.

This time tomorrow, the number of people on the planet will have risen by 192,000 and next week by 1.34 million extra people.

In a year hence, barring a major global catastrophe, there will be 70 million extra people, nearly double the number of Canadians. 

For context, the WHO reported 6.9 million deaths from COVID-19 as of May 2023.

It is hard to talk about population, but when it comes to a sustainable diet, the absolute number of people to be fed and the growth in that number cannot be ignored. 

Sustainable food and food ecology 

Over-reliance on processed foods and 8,000 extra mouths an hour is not even the biggest problem for a sustainable diet for 8 billion people. 

That dubious honour goes to intensifying the food production system and how food is grown, harvested, and stored. This is the topic of our first pillar, sustainable food, and our second pillar, food ecology, is where the solutions can be found.

Food ecology tells us that soils are struggling to deliver crop yields and would fall way short without fertiliser inputs—it is likely that half the nitrogen in your body was fixed from natural gas by the Haber-Bosch process in a fertiliser factory.

According to the FAO, 40% of global agricultural soils are degraded. They are depleted in nutrients, soil carbon, structure and water-holding capacity. Many have turned into dirt. Growing nutritious food at scale in the soil gets more complicated as each cropping cycle takes a little more away than the farmer can afford to put back.

The sustainable diet for all the people alive and those to come must combine what can be grown, where and how, with what should be grown and supplied for metabolic health. This combination must also match ecological capabilities that become increasingly important as the fossil fuel pulse ends—and it will in a decade or two at best. 

Together we have sustainable FED, the food, ecology and diet of feeding everyone well.

The size of the sustainable diet challenge

A sustainable diet sounds easy enough. 

We go back to the diverse diet of our ancestors, cut out the sugar, grains and vegetable oils, and eat plenty of green things.

But we are not starting from scratch.

One in ten, 821 million people in the world are undernourished. They go to bed hungry with a diet that does not supply enough nutrition or energy.

Another 1,900 million adults in the world, one in four, are overweight, with over 650 million of them obese, including one in five children and adolescents. These people are also malnourished. They suffer from poor metabolic health.

And in case you haven’t picked it already, this is not a developing economy problem. Malnourished and increasingly undernourished people are as likely to live in Chicago or Cologne as in Cairo, Cape Town, or Chennai.

Deficiencies in diet still happen when people get their food from intensive production systems that often degrade soil and deplete other environmental values. Many intensive systems are also unlikely to be viable long-term because of this resource mining and high input requirements.

Most industrial food production is unsustainable.

As our sustainable food theme describes, farmers grow enough calories to feed everyone, but the supply chain and social and political constraints mean that only some are fed well.

Food is over-processed, lacks essential nutrition because of depleted soils, and most diets need more variety. Improvements are a challenge for the wallet, the soil, and the food producers. 

The price of food has declined with the proliferation of industrial agriculture. Feeding yourself and your family became more accessible for the majority, so long as the bulk of the food came from staples and their products. Only some people can afford to avoid grains, sugar and processed seed oils. A diet of natural foods can be expensive in dollars and in the time needed to prepare them.

Everyone loves a dollar. The global six continent, just-in-time supply chain is an economic powerhouse. Plenty of shareholders, executives and even employees rely on it for their wealth and status.

It is an individual, a national, and a global challenge to get the diet right.

What sustainably FED suggests…

Our concept of a sustainable diet is inclusive.

It is about what a person eats with all the puzzles that go with diet choices. But diet is also about where that food comes from, how it is grown, and how that comes together in the collective diet.

The D in sustainably FED is both the personal and the collective choice of food, but it is also the supply chain consequences of sustainable food (the F in FED) and food ecology (the E in FED) that tells us how nature supports food production.

This is an expanded vision of what diet means because this view will help achieve a sustainable diet—feeding everyone well for a long time.

A diet focus also helps with direction in ideas to meet the challenge.

We have to consider what food we should eat, how to get a balanced diet to all people, and how to avoid food processing and advertising from running roughshod across the fundamentals of a healthy diet—it might even start with a deep breath. It is time to move away from poor nutritional science and the power of profit in the global food water-holding

It will mean discussing some awkward concepts—redistribution, rationing, alternative food sources—and taking some radical actions.

It will mean avoiding distracting impossibilities. For example, no matter what the vegan community will tell you, it is impossible to feed everyone well, all 8 billion souls and their pets, without livestock. There isn’t enough arable land to grow the necessary protein.  

It will mean avoiding the distracting arguments about one diet or another, how critical it is to fix the climate before we tackle diet, or that veganism will save the planet.

We must become mindful sceptics about our individual and collective diets.

It’s bigger than a personal choice.

Fortunately, we are not the only ones to say any of this. However, we do offer a unique combination of understanding on food, ecology and diet with the intent of sparking in your ideas and sustainability actions.

We encourage you to explore our posts that explore the many nuances of the diet theme or cross over into our discussions of sustainable food and food ecology. We know you will find details to spark your curiosity. 

And on the back of that intrigue, you might even start a company that delivers a sustainable diet to millions of your fellow humans.

If this concept grabs you, take a moment of mindfulness and browse around the sustainable FED sustainable diet theme for more

sustainably FED

Hero image modified from photo by Diana Polekhina on Unsplash


Chris is a latecomer to ecology but has happily landed where he should have been all along as an ecological practitioner in his bush regeneration business. When not out passionately managing land, trawling the evidence on nutrition, diet and health or carefully advising NGOs and government, he grows plants in his commercial nursery

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