peas and a pea pod

Eating plants and animals—humans are omnivores

Some animals eat plants, some eat other animals, some eat both. Humans are one of these animals—humans are omnivores.

Humans are omnivores, our diet has always been flexible and adapted to whatever food we could get our hands on. This is true omnivory—we are not obligated when it comes to food.

The traditional Inuit diet includes some berries, seaweed and plants. Still, mostly it is raw meat from sea mammals (walrus, ringed seal, bearded seal, narwhal, beluga whale and the bowhead whale), land mammals (caribou, polar bear, and muskox), birds and their eggs, saltwater and freshwater fish including sculpin, Arctic cod, Arctic char, capelin and lake trout.

In the Arctic, where the food chain is almost exclusively from the ocean, vegetarianism wasn’t available to humans. The only way to gain plant nutrients was to leverage the roaming capacity and digestive efficiency of the caribou and musk ox by eating the aggregator.

Consequently, 50% of the calories in this Inuit diet come from fat, 30–35% from protein and 15–20% from carbohydrates, mainly the glycogen from raw meat. 

Humans can use protein as an energy source as it is broken down in the liver through gluconeogenesis. Inuit studied in the 1970s had abnormally large livers and high urine volumes to deal with urea, a byproduct of gluconeogenesis. 

Image by Mandy Fontana from Pixabay 

Carbohydrates get plenty of press, but all humans can live without them—carbohydrates are a non-essential nutrient.

Grains and many other plants are relatively low-nutrient foods. The human digestive system is inefficient at extracting nutrients from low-quality food sources. 

Our physiological blueprint is to eat infrequent, nutrient-dense meals—a critical part of freeing up time needed to locate, capture and prepare each meal. Only these foods are few and far between. So it takes time in gathering, hunting and stealing from the hyaenas and time to cement the bonds of trust between the gatherers for what can be complex and risky tasks that is easier with mates. 

Humans eat irregularly but pretty well when we do. Think about this legacy from our ancestors the next time you go to a restaurant, the social place where you eat nutrient rich foods.  

Meat is a nutrient-dense food. The animal that made the protein did it by aggregating nutrients from the plants or other animals that it ate. Essentially it does the foraging for any predator that eats it.

A plant’s most nutrient-dense parts are typically the fruits, seeds and tubers. These are the reproductive parts that evolution determines the plant should invest in to ensure its genetic future. That is where it concentrates its photosynthetic effort.

The laws of thermodynamics require processes of aggregation and allocation to concentrate energy and nutrients.  Left to nature, energy would dissipate. It is the unique feature of biology that defies this entropy. Plants do it by  focusing the sun’s energy. Animals do it by using the energy plants or other animals.

You know most of this Ecology 101. But it is worth the reminder of where humans sit in this ecology. Humans are animals and humans are omnivores—we get our energy from plants and animals.

And our evolutionary preference is for nutrient-dense food.

elephant herd startled by the camera in mopane woodland, Okavango Delta, Botswana

Elephants have the opposite diet physiology to humans, using a large body to consume and rapidly throughput a vast volume of low-quality food, primarily as cellulose from grasses, leaves and tree bark. Photo of an elephant herd in the Okavango Delta, Botswana by Alloporus.  

Humans are omnivores… and adaptive opportunists.

As primates, humans are not obligate herbivores or carnivores. Circumstances and choices can make us either. Nutrient-dense meals can come from plants or animals or a mixture of both in various proportions. In our evolutionary past this flexibility was a huge advantage.

Our ancestors could survive and prosper in almost any habitat because they could gain access to whatever nutrient-dense food was available—everything from a walrus to a walnut. All that mattered was that it was edible and provided enough nutrition to free up time to find the next morsel. 

Plant or animal or fungi, it did not matter.

Modern humans are omnivores—we eat a bit of everything—just as our ancestors did in the forest and savannas of Africa. Back in the day, there was little choice than to forage widely for high-value foods: the trees in fruit, the tubers beneath a particular type of foliage, some flowering grasses, animals we could catch, and the occasional carcass. And everyone had an eye for protein.

Humans are opportunists and always have been. We eat what we can with a preference for sugary, salty and fatty foods wherever possible.

The technical term is adaptive. 

Humans are genius-level at adapting to what food is on offer whilst bending nature to produce more sugar, salt and fat that we like.

So will we change our ways?

Can we alter the eating habits locked into our DNA and honed by our ancestors?

Should we even try?

Well, there is a lot of noise telling us that we should from meatless Monday to full on veganism, typically argued as the only way to save the planet. 

And the message is getting through.

plate of stir-fried noodles with vegetables for humans are omnivores

Photo by Toa Heftiba on Unsplash

Please eat less meat 

We are told to eat less meat because it is healthier. And the message is getting through in the UK.

Health behaviour researchers at the University of Oxford analysed data from the annual  National Diet and Nutrition Survey. They found that between 2008-9 and 2018-19, average meat consumption decreased from 103 to 86 g per person per day, a 17% reduction in a decade. 

There was an absolute daily reduction of 13.7g of red meat, 7g of processed meat, and a 3.2g increase in white meat consumption.

A substantive change. 

This could be a shift towards cheaper options, an explanation English Franciscan friar William of Ockham would have offered after a bit of thought.

But there are other substantial trends.

man's hand holding a large chunk of beef on a chopping board

Photo by Armando Ascorve Morales on Unsplash


Cadbury, the biggest confectionery company in the UK owned by US giant Mondelez, recently announced a vegan alternative to the Dairy Milk chocolate bar. 

The Cadbury Plant Bar substitutes almond paste for the “glass and a half of milk” said to go into every Dairy Milk bar.


All the feel-good of chocolate without animal products and a reflection of a growing market of people who only eat plants.

Journalist and author Anthony Andrew pulled a few numbers on veganism for an article on the unstoppable rise of the plant-based diet

  • 79 million vegans in the world 
  • 500,000 participants in Veganuary in the UK in 2021, up 100% on 2019 
  • 66% of UK vegans are female 
  • 163% increase in Deliveroo’s vegan orders in the UK in 2020 over 2019 
  • 18,000 food and drink products with the Vegan Society’s vegan trademark
  • $24.3 billion global vegan food market by 2026

One in one hundred doesn’t sound like many. A busload of people randomly selected from the global population would have one vegan onboard, but the proportional jumps suggest a stirring of the dahl.

It seems that more and more people are thinking about herbivory and ignoring the fact that humans are omnivores and perhaps even innately carnivores. 

vegetables on a chopping board

Photo by engin akyurt on Unsplash

What sustainably FED suggests

Humans eat animals and animal products. We always have because while our physiology is flexible enough to cope with multiple energy sources, the concentrated nutrient in animal products was an efficient way to gather food before it appeared on supermarket shelves.

Our diet has always been flexible and adapted to whatever food we could get our hands on before the hyenas. This is true omnivory—we are not obligated when it comes to food.

Humans can happily be vegetarians or vegans, for our physiology is flexible enough to allow it. And there are plenty of reasons for herbivory, including the hope of that vegetarianism might save the planet. But it is not compulsory; just ask the Inuit.

Sustainably FED believes that a sustainable diet must be sustainable for a person’s health, wallet, the soil, and the producers that supply the food. It also has to match not just the idea of our physiology but its evolutionary past.

Animals and plants play a massive role in this definition, not least because humans have always eaten animals from seals to termites for the nutrient-dense, energy rich hits of high quality foods.

Humans are omnivores for a reason.

Science source

Stewart, C., Piernas, C., Cook, B., & Jebb, S. A. (2021). Trends in UK meat consumption: analysis of data from years 1–11 (2008–09 to 2018–19) of the National Diet and Nutrition Survey rolling programme. The Lancet Planetary Health, 5(10), e699-e708.

Hero image from photo by engin akyurt 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.

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