Can you achieve a balanced diet by eating only meat? A look at the scientific evidence
A diet that involves eating meat all the time sounds like a meat-lover’s dream. And you may have heard various social media influencers tout the health benefits of such a diet. Sounds like a win-win? Not so fast. As with most things in life, reality isn’t that simple.
The carnivore diet consists of exclusively consuming foods of animal origin. It includes meat of course, but fish, seafood, eggs, milk, and dairy products such as cheese and yogurt can also be part of the carnivore diet. A meat-heavy diet has traditionally been practiced by Inuit societies out of necessity, due to the Arctic environment. This has been presented as evidence that a carnivore diet can be a balanced and healthy one. In the context of the developed world, some websites promoting the carnivore diet suggest the diet’s chief benefit lies in its extremely limited carbohydrate content, which is otherwise a major source of calories in the standard American adult diet.
However, experts have pointed out that the Inuits don’t only eat meat, contrary to a popular misconception, and the food they consume tends to be less refined. For example, they also eat a lot of seafood and eat their meat raw, which is higher in vitamin C than cooked meat. This makes it easier for them to meet the daily nutritional requirements, in contrast to the all-meat diet that some, like podcaster Mikhaila Peterson, tout.
While there isn’t evidence that following a diet based on animal products has health benefits, excluding plant-based foods from the diet can be detrimental to health.
In this article we will explain some of the limitations of the carnivore diet, and its possible negative effects on health according to the current evidence.
Meat-only diets are rich in certain nutrients but deficient in others
There are several variations of the carnivore diet. Some people who self-identify as following a carnivore diet consume fruits or nuts, while others don’t consume seafood, milk or dairy products.
One particularly restrictive variation of the carnivore diet is the “lion diet”, promoted by blogger Mikhaila Peterson and her father, psychologist Jordan Peterson. This diet is based on exclusively consuming ruminant meat, which includes domestic animals such as beef and lamb, as well as game animals such as elk or venison. Some have called this diet an “all-beef diet”.
While it’s possible to obtain all essential nutrients from animal sources, not all animal-based foods contain the same nutrients. Meat is an excellent source of protein, fatty acids, and a wide range of key vitamins and minerals, including iron, zinc and various B vitamins, but it isn’t a good source of calcium, whereas milk and dairy are.
Another important nutrient that is generally lacking in meat is Vitamin D which is necessary for calcium absorption and bone development. Humans can produce their own Vitamin D during exposure to sunlight, but people with little exposure to sunlight may be deficient in vitamin D, which can cause calcium malabsorption. Dairy products, eggs, and fatty fishes like salmon are good sources of vitamin D, but meat contains only a negligible amount.
Vitamin C is a nutrient with antioxidant properties that plays a key role in important bodily functions, such as collagen production and wound healing. The main sources of vitamin C in the diet are vegetables, citrus fruits in particular, while its presence in meat is minimal. Vitamin C deficiency causes various disorders and can lead to scurvy. Scurvy is a disease caused by vitamin C deficiency, which causes bleeding in the gums and under the skin, and can lead to anemia and tooth loss.
Variations of the carnivore diet that exclude milk, dairy, and fish, or fruits and vegetables, like the “lion diet” can lead to important nutritional deficiencies that lead to illness. Several celebrities tried the carnivore diet and some experienced health problems as a direct result of excluding plant-based foods from their diet. One such example is UFC commentator and podcaster Joe Rogan, who developed a severe case of diarrhea after several weeks of eating exclusively animal-based foods. Singer James Blunt developed scurvy after eating exclusively meat for two months.
Apart from vitamin C and D, meat is poor in other nutrients that can be found in plant-based food, like vitamin E, which plays a role in the immune response and has an antioxidant effect. Deficiency can cause retinopathy (damage to the retina) and peripheral neuropathy (damage to the peripheral nerves). The main sources of vitamin E in the diet are vegetables, especially vegetable oils, whereas animal-based products are poor sources of vitamin E, with the exception of egg yolks.
In addition to vitamins, the human body needs a number of minerals to perform various biological functions. Since we can’t synthesize these minerals, we must incorporate them in the diet. As different foods contain different amounts of minerals and other nutrients, a balanced diet facilitates an adequate intake of the various minerals we need. Conversely, an unbalanced diet increases the risk of nutritional deficiencies.
Calcium is an essential element for bone development, muscle contraction (including the heart), and other body functions. Calcium deficiency can cause osteoporosis or rickets. The main sources of calcium in the diet are dairy products, as well as some vegetables and fish, while meat is poor in calcium. An exclusively meat-based diet can compromise calcium levels over time.
Magnesium is another essential dietary mineral involved in numerous body functions, such as protein synthesis, muscle and nerve function, and regulation of blood pressure. Magnesium deficiency can lead to high blood pressure, migraines and osteoporosis. Vegetables are a good source of magnesium, especially nuts and seeds, while meat and fish contain a small amount.
Last but not least, manganese is a trace element involved in the formation of bone and essential for the functioning of various enzymes. While vegetables and shellfish are good sources of manganese, the amount of manganese in meat is very small.
Some promoters of the carnivore diet recommend various ways to circumvent potential nutritional deficiencies. For example, some suggest consuming bone broth to increase calcium and magnesium intake. However, the calcium and magnesium content in bone broth is considered to be small, which raises questions about how effective such an approach is.
Another suggestion is eating meat raw, since a significant amount of vitamins are lost during cooking[8,9]. But this poses its own dangers, as raw meat can contain bacteria like Salmonella that cause food poisoning.
In summary, although eating foods of animal origin can allow us to obtain all essential nutrients, certain variations of the carnivore diet that exclude dairy, plant-based food and seafood will lack a significant amount of some important nutrients. As mentioned before, such deficiencies can lead to health problems, like scurvy.
Excessive protein and fat consumption can cause several health disorders
Although red meat is rich in several nutrients and can be part of a balanced diet, the ruminant meat-only diet promoted by some like Peterson is likely to result in excessive red meat consumption, which is associated with several health disorders. Red meat is high in saturated fat, which can increase low-density lipoprotein (LDL) cholesterol, commonly known as “bad” cholesterol, known to increase our risk of heart disease.
High levels of LDL cholesterol are associated with increased risk for atherosclerosis, a buildup of fat that can damage and clog arteries, thus increasing the risk of heart attack and stroke. Low-carbohydrate, high-fat diets—like Peterson’s lion diet—have been shown to increase LDL cholesterol levels in healthy adults.
Another concern related to the carnivore diet is the possible harmful effects of excessive protein intake. Chronic intake of above two grams of protein per kilogram of body weight per day in adults may cause digestive, renal and vascular abnormalities and should be avoided. This is due to the fact that protein metabolism generates ammonia, a toxic substance that must be eliminated through urine. Eating too much protein can generate more ammonia than the liver, intestine, and kidney can manage to excrete.
Notably, promoters of the carnivore diet do recommend protein intake close to or higher than these levels, which shows that potentially harmful levels of protein intake are achievable with a carnivore diet.
In addition, excessive red meat consumption is also associated with an increased risk of cancer. In 2015, the World Health Organization classified the consumption of red meat as “probably carcinogenic to humans”. This was based on limited evidence that the consumption of red meat is linked to a higher risk of several types of cancer (colorectal, pancreatic, and prostatic), and strong mechanistic evidence indicating that red meat consumption can have a carcinogenic effect, as it’s linked to DNA damage and to the appearance of tumor-associated lesions.
A meta-analysis that included 24 prospective studies found that high intake of red and processed meat was associated with significantly increased risk of colorectal, colon and rectal cancers.
Another review that included 72 meta-analyses found that red and processed meat consumption was associated with increased risk for non-Hodgkin lymphoma, as well as bladder, breast, colorectal, endometrial, esophageal, gastric, lung, and nasopharyngeal cancers, and overall cancer mortality.
Lack of dietary fiber can affect the gut microbiota
One of the biggest limitations of a diet that restricts vegetable intake is the reduction of dietary fiber, as animal-based foods don’t contain fiber. Dietary fiber is composed of carbohydrate polymers present in vegetables, like cellulose and pectin which are components of plant cells, which are neither digested or absorbed, since humans don’t have the required enzymes to do so.
Even though we can’t digest dietary fiber, it plays an important role in the body. Scientific evidence shows that an adequate intake of dietary fiber is associated with several health benefits, such as reduced levels of cholesterol, better regulation of blood glucose, prevention of constipation, and weight control.
Studies have shown that diets rich in fiber can reduce LDL cholesterol, which is linked to a lower risk of developing cardiovascular disease and arteriosclerosis. Furthermore, an increased intake of dietary fiber has been shown to reduce blood pressure in people with cardiovascular disease and hypertension.
Research is ongoing into how dietary fiber exerts such effects. This could be related to the microbes that colonize our gastrointestinal tract, or gut microbiota, as dietary fiber is fermented by bacteria in the gastrointestinal tract and can influence the composition of the gut microbiota, as well as microbial metabolic activities.
Some research suggests that fiber intake influences the gut microbiota in a positive way in metabolic diseases like obesity and diabetes, and reduces the risk of cardiovascular diseases.
In addition, evidence from animal and human studies shows that dietary fiber provides important clinical benefits in patients with inflammatory bowel disease (IBD). Inflammatory bowel disease is a medical term that includes both Crohn’s disease and ulcerative colitis, diseases characterized by chronic inflammation of the gastrointestinal tract. The American Gastroenterological Association recommends that patients with IBD consume more fiber as it can help improve symptoms.
While a person may be able to consume some form of the carnivore diet in the short run without many ill effects, it’s clear that the diet comes with significant restrictions that can eventually prove detrimental to human health. Nutritional deficiencies, like a lack of vitamin C, can soon lead to illness, like scurvy. And in the long run, excessive consumption of red meat, which is rich in protein and fat, but deficient in carbohydrates and dietary fiber, increases the risk of heart disease and certain cancers. Ultimately, low-fat, high-fiber diets that include a variety of foods—which the carnivore diet is unlikely to be—are the ones that have been reliably shown by scientific studies to produce health benefits.
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