You’ve probably heard of the ketogenic diet and you may have heard of the paleo diet – but have you heard of the carnivore diet? This emerging trend takes low carbohydrate diets to a new extreme.

The carnivore diet excludes all plant foods; only foods derived from animals are consumed, including meat, fish, animal fats (for example, lard and ghee) and (low lactose) dairy foods. So, breakfast might be eggs and bacon with cream, lunch could be cheese-topped meatballs – no herbs added – with chicken breast, and finally, roast beef and salmon for dinner.

Advocates of the carnivore diet contend that plant toxins and residual pesticides used in plant food production are harming our health. They claim that starchy foods only became a major part of the human diet with the agricultural revolution.

It’s also been proposed that eliminating all plant foods is the best way to go sugar-free for weight control and metabolic health.

Authors of carnivore diet books tend to frame their subject as the answer to the global problem of obesity and non-communicable chronic diseases and often claim that decades of nutritional science research have culminated in flawed dietary recommendations.

Most of these authors draw on the argument that Homo sapiens evolved to hunt for meat and fish, and that plant-eating was only a backup plan for times of animal food scarcity.

What could you expect if you consumed only animal-sourced foods for a significant period of time? Unfortunately, there’s no scientific evidence available on the health impact of excluding all plant foods from the diet.

The only available sources of information are anecdotal reports and testimonials, reporting better weight management, improved heart and metabolic health, superior cognitive function, lower inflammation, better digestive function, and resolution of auto-immune diseases.

Side effects are similar to those reported for the ketogenic diet – bad breath, constipation, diarrhoea, headaches, dehydration and other symptoms associated with being in a state of ketosis. This is when the body has used up all its glycogen stores and breaks down fat into ketone bodies that can be used as a source of energy, instead of glucose.

These side effects may eventually subside as the body adapts to the diet after about a month.

As for the nutritional benefits of the carnivore diet, meat is an excellent source of high-quality protein, iron, zinc, selenium, vitamin D and vitamins B6 and B12 – the latter can only be obtained from animal-source foods.

Fish contributes high-quality protein, omega-3 fatty acids, vitamin D, selenium and iodine. Dairy foods are also rich in high-quality protein, as well as calcium, iodine and B vitamins.

The UK dietary guidelines, embodied in the NHS’s Eatwell Guide, recommend eating dairy foods, lean meats (no more than 70g per day of red or processed meat) and two portions of fish per week – one of which should be oily fish.

However, the Eatwell Guide also recommends consuming at least five 80g portions of fruits and vegetables per day, and that a third of what we eat should be wholegrain and higher-fibre starchy foods.

Cutting out fruits, vegetables, nuts and seeds, and wholegrains on the carnivore diet would mean zero fibre intake. Fibre is essentially the intact cell walls of plants that are poorly digested, with unknown long-term consequences for gut and heart health if cut out entirely.

In fact, there is strong global consensus that increased dietary fibre consumption is associated with lower risks of cardiovascular disease, type 2 diabetes and colorectal cancer, whereas high red and processed meat consumption increases risk.

Evidence from randomised controlled trials shows that plant foods rich in soluble fibre lower blood low-density lipoprotein (LDL) cholesterol – the so-called ’bad‘ kind – and triglyceride concentrations. This decreases the rate of progression of atherosclerosis, the fatty lesions that can damage and block arteries and cause coronary heart attacks and stroke.

Conversely, fatty meats and butter can raise LDL cholesterol.

Plant foods are also rich in potassium and vitamins C, folate and other micronutrients, all essential for health – and derived mainly from fruit and veg.

Additionally, we know that healthy plant-based diets are associated with more diverse and beneficial gut microbiome profiles, resulting in microbial fermentation products from fibre and non-nutrient bioactive compounds that may reduce inflammation.

Supporters of the carnivore diet commonly make the argument that subsisting entirely or nearly entirely on animal-sourced foods is close to the natural human diet, aligned with what was eaten in early human history.

Biological anthropologists, however, would point out that the anatomy of our brains, teeth and intestines show that we evolved as highly resourceful and flexible omnivores who can adapt to many varied environments to meet our nutritional needs from both animals and plants.

Collectively we must accept that global food production needs a major shake-up if population nutritional needs are going to be met while also attempting to hold back the looming climate change disaster. Reducing meat consumption is an essential component of the move towards sustainable, healthy food systems.

The carnivore diet flies in the face of this global mission for planetary health, for the sake of perceived personal gains. Regardless of the potential long-term harm to healthy life expectancy, this seems to be the ultimate selfish act.

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