Carnivorous diet rejected: harmful for arteries, microbiota and tumors

When we scroll through social media, the algorithm increasingly offers us videos of a muscular influencer biting into a raw liver and swearing he's never had so much energy. But the carnivorous diet trend doesn't stop at the digital world: more and more often we read articles in newspapers and magazines that tell stories of rebirth thanks to this extreme regime, and television is also increasingly hosting testimonials from people who say they've solved health problems simply by eliminating all foods that aren't of animal origin.

An unfounded health message

The message is clear: Eat only meat and you will be lean, strong, free from inflammation.

But what is the carnivore diet really? It means eating only meat (red, white, offal, fish) and fatty derivatives such as butter, lard, aged cheeses, leaving vegetables, cereals, legumes and even olive oil off the plate. A diet that eliminates entire food groups and, for this very reason, gives lightning-fast results – the scale goes down, the belly deflates – giving the impression of a metabolic miracle. Too bad science tells a different story.

Since the 1960s, we have known that regular intake of saturated fats – abundant in red and processed meats – increases LDL cholesterol and with it the risk of heart attack and stroke. A prospective study published in JAMA Internal Medicine in October 2024 followed over 400,000 US adults for 24 years and shows that replacing 5% of energy intake from animal fats with vegetable fats is associated with a reduction in cardiovascular mortality of up to 30%. On the cancer front, the International Agency for Research on Cancer has classified processed meats as “certainly carcinogenic” and red meats as “probably carcinogenic”: a daily consumption of 50?g of cured meats increases the risk of colorectal cancer by 18?%. Things are no better with type 2 diabetes: in the EPIC InterAct study, which followed 340,000 Europeans for twelve years, those who consumed the most red meat had a 22 percent higher risk than moderate consumers.

Let's consider what's missing: fiber.

Added to these dangers is a less obvious but equally crucial one: the complete absence – or almost – of fiber, and here it is worth dispelling a frequent misunderstanding. When we discuss the risks of a diet we cannot limit ourselves to pointing the finger at what it contains in excess (saturated fats, processed meats): we must also evaluate everything that disappears from the plate. A diet that celebrates steaks and ribs, by definition, leaves very little room for vegetables, fruit, legumes and whole grains, that is, the foods on which our microbiota has evolved.

Gut bacteria live on fermentable fibers and when the intake drops below 25–30 grams per day they rapidly change identity: the strains that produce short-chain fatty acids – our natural anti-inflammatories – are reduced and pro-inflammatory microorganisms proliferate. The result is a dysbiosis that increases intestinal permeability, increases circulating cytokines and worsens glycemic control. A study published in Gut in 2022 showed that just four weeks of a high-protein, low-carb diet are enough to cause bacterial biodiversity to collapse by 30% and cut fecal levels of butyrate, the metabolic “gold” of the colon, by 40%. Returning to a high-fiber diet only partially repairs the damage, a sign that the systematic elimination of vegetables leaves deep scars on our internal ecosystem.

A mirror for larks

Proponents of the carnivore diet argue that the regime lowers triglycerides and blood sugar, and causes inches to drop off your waistline in just a few days. This effect is true, but it’s a decoy: by abruptly cutting out carbohydrates and fluids, your glycogen stores are depleted and you lose water, not fat. In the medium term, the parameters worsen. A Canadian study in Nature Cardiovascular Research found that ketogenic diets—close cousins ​​of the carnivore diet—accelerate the formation of atherosclerotic plaque; a clinical follow-up of 200 American “carnivores” found LDL levels above 190?mg/dl in 90?% of participants after six months. It’s worth noting, at this point, that proponents of the carnivore diet often boast of perfect blood tests after just a few weeks or months.

But our body has an extraordinary ability to compensate in the short term, and the mechanisms that lead to the onset of a tumor or cardiovascular disease often take years or decades to manifest themselves. High cholesterol, chronic inflammation, intestinal dysbiosis: all these processes are triggered slowly, sometimes silently, without giving obvious clinical signs until the damage has already occurred. This is the case, for example, of atherosclerotic plaques, which can accumulate for decades before causing a heart attack or stroke, or of cellular mutations that, favored by a proinflammatory state and an excess of carcinogenic substances, transform into neoplasms after long latency periods.

Double the risk of cardiovascular events

Thinking that six months of "normal" tests guarantees the absence of negative effects is a dangerous illusion. The effect is true, but it's a decoy: by abruptly cutting carbohydrates and liquids, glycogen stores are emptied and water, not fat, is lost. In the medium term, the parameters worsen. A study published in JACC Advances in June 2024 observed that low-carb, high-fat (LCHF) diets - close cousins ​​of the carnivore - are associated with a marked increase in LDL cholesterol and apolipoprotein B, and almost double the risk of major cardiovascular events (MACE) compared to those who follow a standard diet.

An animal diet is bad for the environment

If the biological bill is high, the ethical and environmental one is no less so. To produce a kilo of beef, an average of 15,000 liters of water are needed and 60?kg of CO? are emitted, equivalent to ten times more than a kilo of legumes. The FAO estimates that livestock farming generates 14.5?% of all climate-altering emissions; pushing towards an entirely animal-based diet would mean multiplying deforestation and resource consumption. Even the wallet suffers: a week of quality steaks can double the expense compared to a cart full of fresh vegetables and cereals.

The Planetary Health Diet

Yet the evidence on what really extends life goes in the opposite direction. Large prospective studies – from the Adventist Health Study to the Nurses' Health Study, via EPIC?Oxford – converge in indicating that predominantly plant-based diets, rich in legumes, whole grains, nuts and vegetables, and with red meat relegated to occasional consumption, reduce all-cause mortality by up to 30?%. The EAT?Lancet Commission speaks of a “planetary health diet”: half the plate vegetables and fruit, a quarter whole grains, the rest mostly plant-based proteins, with red meat up to 14?g per day. These are the same guidelines that FAO and WHO recommend to combine human health and sustainability.

In short, the carnivorous diet is fascinating because it promises immediate results and is cloaked in ancestral rhetoric, but it is a dress that does not fit our metabolism or that of the Earth. The price to pay - stiff arteries, impoverished microbiota, rising cancer risk and an off-scale ecological footprint - is too high for a passing fad. Better to focus on a varied, colorful and fiber-rich diet: that's where science finds the most solid evidence of a long and healthy life.