Vegan vs Carnivore: What Does The Science Actually Say?

For this post, I spoke with registered dietitians Dahlia Marin, RDN, LD, CGN, James Marin, RD, EN, and Vahista Ussery, MS, MBA, RDN for the most comprehensive and evidence-based analysis of the two diets.

The debate continues--especially on social media--between carnivores and vegans. These two diets are essentially the exact opposite, but which is actually healthier? Dietitians set the record straight by diving into what the science actually tells us about the pros and cons of each diet.

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What Is A Vegan Diet?

Let's first address what kind of vegan diet I'll be discussing here, because it's important to distinguish. A whole foods plant-based diet is made up of legumes, whole grains, fruits, vegetables, nuts, and seeds.

However, a vegan could also technically eat lots of processed foods including Oreos, chips, and vegan ice cream. I'll be comparing the carnivore diet to the whole foods plant-based diet because it's the type of plant-based diet that is backed by science and makes for a more accurate comparison.

While the term "vegan" has been around since 1944 when Donald Watson found the Vegan Society in the UK, the idea of abstaining from eating animal foods has been around for thousands of years, typically as a religious or philosophical practice of "non-violence."

Environmental impact and animal welfare aside, many people follow a vegan or vegetarian diet due to the health benefits. Plant-based eating has been shown to be preventative for several chronic diseases including heart disease, diabetes, cancer, obesity, gut diseases, and more.

What Is A Carnivore Diet?

The carnivore diet is a trendy new diet that excludes all plant-based foods and involves consuming only animal-based foods, with particularly high amounts of fatty red meat. The diet also includes fish, eggs, bone broth, milk, butter, aged cheese, lard, tallow, and grass-fed organ meat. Salt, pepper, and herbs are allowed, even though herbs are technically plant-based.

Followers of the carnivore diet exclude all fruit, vegetables, high-lactose dairy products, added sugars, processed foods, grains, nuts, seeds, legumes, and low-quality or processed meats (with the idea that those following a carnivore diet should choose grass-fed and pasture-raised meats).

Advocates of the carnivore diet claim that it improves inflammation, gut health, and autoimmune conditions and believe that we should be eating like our cavemen ancestors. However, essentially all claims made in favor of the carnivore diet are anecdotal and have no basis in science.

The heavy meat diet was popularized in the mid-2010s by a medical doctor (specifically orthopedic surgeon) and athlete named Shawn Baker, who claimed it helped improve his health. In an interview with Thomas DeLauer, Baker himself explains how the diet is not for everyone -- especially not those who dislike meat, those with financial constraints, those who have no issues with their current diet, and children.

Dr. Shawn Baker also acknowledges that the carnivore diet has long-term health risks including heart disease, but claims that for people with debilitating acute issues like autoimmune disease or gut problems, short-term relief tends to be more important to them.

Registered dietitian and culinary nutrition expert Vahista Ussery, MS, MBA, RDN further warns, "Before going on the carnivore diet, consider your current heart health. Please do not try this diet if you have high cholesterol or any cardiac concerns. Also, consider how eating in this way will impact your social and family life. Can you dine with others comfortably? This diet would also be extremely expensive. Do you have the budget to afford this style of eating?"

What Do The Whole Food Plant-Based Diet and The Carnivore Diet Have In Common?

If these two are essentially the exact opposite diets, how can we possibly have people who claim that either diet made them feel better?

Both diets avoid processed foods, added sugars, alcohol, and processed meats, all of which have plenty of research pointing to negative health consequences when eaten regularly or in excess. Therefore, some of the health benefits of both diets can be related to the avoidance of these foods.

Ussery brought up another great point of commonality, "I think one more commonality would be the need for creativity and knowledge of culinary techniques in the kitchen. I find that with the vegan diet, incorporating spices, herbs, and techniques from a variety of cultures is important to add variety and fun to meals."

"With the carnivore diet being so restrictive, knowing how to prepare all of the animal products properly and with culinary prowess could make the diet somewhat more palatable. I, however, could not imagine only eating animal products. How boring and heavy!"

Science-Based Health Comparison of Vegan and Carnivore Diets

Let's get into what the science says in order to get a better perspective on what has actually been tested and confirmed about nutrition and health.

It's important to understand and keep in mind that there is a huge difference between meta-analyses that look at thousands of people from multiple different studies over a long period of time compared to one person's short-term experience posted on social media. This is why we always want to look at the scientific evidence as opposed to what self-proclaimed "experts" claim online.

Gut Health

One of the biggest arguments in favor of meat-based diets on social media is that it "improves gut health." However, this is exactly the opposite of what the science says.

I spoke with Dahlia Marin, RDN, LD, CGN and James Marin, RD, EN, the registered dietitians specializing in gut health behind the popular Instagram and private practice Married to Health, to get their take on vegan and carnivore diets.

Bloating and Gas

According to the Marins, "Our gut thrives on diversity, whereas the carnivore diet is the exact opposite of diverse. The claims that 'the carnivore diet promotes gut health' are not scientifically backed and come from misinformation about the gut. While the carnivore diet may initially reduce bloating and gas due to the absence of fiber in the diet, the long term effects can be detrimental. We always like to remind- a lack of symptoms is not equivalent to a cure."

Microbiome Diversity

Dahlia and James shed light on the possible reason why some people can't tolerate high amounts of fiber: "Our dietary patterns have been altered over many generations along with our stress levels and geographic residences, which has ultimately altered our gut microbiomes. Due to the altered microbiota, we have lost the ability to digest certain plants over the decades."

However, this doesn't mean that we should avoid fiber and plant-based foods altogether. The Marins warn that eliminating plants from our diets will "cause further destruction of the important species in our gut" and decrease our microbiome's diversity. Because fiber is incredibly important to long-term gut health, the Marins work with their patients to "temporarily eliminate these foods and slowly reintroduce them at tolerable levels."

Plant-based foods contain high amounts of dietary fiber (which is not present in animal-based foods). Fiber is fermented into short-chain fatty acids (SCFAs) by the bacteria in our gut, and these short-chain fatty acids improve intestinal barrier function, inhibit the inflammatory response, and help regulate immune function.

Alternatively, animal protein has been linked to higher amounts of TMAO and "bad" gut bacteria associated with inflammatory bowel disease, liver cirrhosis, and colon cancer. In a dose-response analysis on over 4 million people, each 100g increase in total meat consumption per day increased risk of inflammatory bowel disease by 38%. See the cancer section below for more on meat and colon cancer risk.

Inflammation

Although people on social media repeat the unbacked claim that a carnivore diet decreases inflammation, numerous studies and meta-analyses show that a higher intake of animal foods, processed foods, alcohol, and sugar correspond to a higher level of inflammatory markers in the gut, while plant-based foods are linked to less inflammation due to the presence of antioxidants and fiber's role on the gut microbiome.

Food Sensitivities

It could also be true that someone has an unknown food sensitivity and the carnivore diet removed it, causing short term relief. But this does not mean that the carnivore diet is healthy long-term or for other people. It could simply be that this particular person used it as an elimination diet to remove a triggering food for them.

Long-Term Gut Health

It's clear from research that a predominantly plant-based diet is most beneficial for our guts. The Marins recommend that "at least 80% of your diet should be from plants, while the other 20% can be from other sources," and they encourage their patients to eat "30 or more plants per week to achieve a more diverse microbiome and improve their gut’s tolerance to fiber."

For long-term gut health, the Marins say that "it's essential to not just include plants, but include mostly plants."

Cancer

A carnivore diet will be naturally high in saturated fats due to high intake of fatty red meats, lard, tallow, butter, and other high-fat animal foods. A recent systematic review and meta-analysis of 55 different studies found that a high intake of saturated fat is correlated with increased risk of breast, prostate, and colorectal cancers.

Another meta-analysis linked high red meat intake to breast cancer, endometrial cancer, colorectal cancer, colon cancer, lung cancer, and hepatocellular cancer. High red meat intake is believed to be linked to cancer due to heme iron, N-nitroso compounds from nitrates and nitrites, and heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) from cooking it at high heat.

The American Institute for Cancer Research (AICR) recommends avoiding processed meat completely and notes that consuming more than 12-18 oz of red meat per week increases risk of colorectal cancer. Clearly, a carnivore diet would be eating much higher than this amount.

Alternatively, the AICR recommends that at least two-thirds of your plate should be plant-based foods for cancer prevention since whole plant foods contain high amounts of antioxidants that reduce oxidative stress and help prevent cancer.

Heart Health

Plant-based diets have long been shown in the scientific literature to reduce the risk of heart disease (both atherosclerosis and high blood pressure), type 2 diabetes, cancer, and premature death. The biggest reasons for this are the presence of fiber, antioxidants, potassium, and magnesium -- all of which are completely absent or found in very low amounts in meat and animal products.

Furthermore, plant-based foods (aside from coconuts and palm) are naturally lower in saturated fats and higher in unsaturated fats. Alternatively, fatty red meat and high fat animal products are high in saturated fat, leading to higher LDL cholesterol (and therefore increase risk of heart disease) in those who consume excess amounts.

Nutrient Deficiencies

One of the biggest arguments against vegan diets is that it increases risk of nutrient deficiencies. However, any diet can have nutrient deficiencies when not properly planned.

While it's true that a poorly planned vegan diet can be low in iron, calcium, vitamin D, zinc, iodine, omega-3s, vitamin B12, and choline, these essential nutrients can all be obtained from certain plant-based foods, fortified foods, and/or supplementation.

For example, beans are high in iron, fortified plant milks are high in calcium and vitamin D, nutritional yeast is high in vitamin B12, flax seeds and algae are high in omega-3s, legumes and grains are high in zinc, soy is high in choline, and iodized salt provides iodine.

However, a carnivore diet will inherently be deficient in fiber, vitamin C, folate, vitamin E, potassium, magnesium, and antioxidants. Contrary to what some carnivore diet enthusiasts on social media proclaim, you cannot get all the nutrients you need from red meat.

Nutrient Toxicity

There are also potential concerns from nutrient toxicity due to the high amounts of bioavailable nutrients in red meat and liver. For example, excess heme iron (the iron present in animal-based foods) is linked to colorectal cancer. The risk can be reduced from adequate intake of calcium and from antioxidants like vitamin C (which wouldn't be adequate on a carnivore diet).

Similarly, vitamin A (a fat-soluble vitamin which is present in very high amounts in liver and some supplements) can lead to extremely severe birth defects when consumed in excess during pregnancy. This is a major concern as I've seen many followers of the carnivore diet recommend consuming liver and liver supplements in pregnancy, which could have potentially dire consequences.

sugar on a spoon with a raspberry on top

Other Health Outcomes

A large number of studies have pointed to increased risk of heart disease and diabetes from both processed and unprocessed meat intake. There's also been shown to be an increased risk of kidney stones with higher meat intake.

Furthermore, a systematic review and meta-analysis of observational studies found an association between red meat, trans fats, and saturated fat and a higher risk of endometriosis. For more in-depth information on plant-based diets vs animal-based diets on health outcomes of the gut, kidneys, heart, diabetes, cancer, and more, see my post on the benefits of a plant-based diet.

Ussery reiterates, "There is so much research correlating plant-based/plant-forward diets to longevity and a healthy body!"

Dietitian's Overall Thoughts on The Carnivore Diet

Ussery sums it up well when she states, "I have a lot of concerns with someone following the carnivore diet, and would not advise anyone to follow this restrictive style of eating. If already on the carnivore diet, I would recommend keeping the time on the diet short for worry of nutrient deficiencies, digestive issues, and cardiovascular damage."

"Animal products are a great source of protein and also provide various vitamins and minerals, but they simply cannot supply all that you need. Furthermore, they do not contain any fiber, which is essential for digestive and heart health. Your gut microbiome will truly suffer. The little microbes in our gut like plants to feed them. By eating all meat, you will encourage bad bacteria to grow, which is correlated with many health ailments. You might also experience constipation if going full carnivore."

"Animal products also are missing phytonutrients, that work as super powers if you will, in your body. Phytonutrients are what provide plants with color and protection, and work to protect our bodies once consumed from diseases like cancer, inflammation, and illness. It is essential that we eat a variety of fruits, vegetables, whole grains, legumes, nuts, and seeds for our health. We have abundant evidence to support that these foods are the essence of health and longevity."

"Animal products can also be high in saturated fats, which is correlated to increased LDL cholesterol. If following the carnivore diet, it would be good to focus on sources that provide omega-3 fatty acids to fight inflammation and protect your brain and heart. Omega-3 fatty acids are found in fatty fish, grass fed meats, and some eggs. Also, remember that red meat is correlated with colon cancer, and should ideally be limited in the diet."

Dietitian's Overall Thoughts on The Vegan Diet

Ussery continues, "For the vegan diet, I think it is always important to specify that a whole foods vegan diet can be a healthy eating pattern. There are many ultra-processed vegan foods that people confuse with being healthy, but they are still ultra-processed and not good for health. You can be vegan and eat a ton of junk food."

"If following a whole foods vegan diet that emphasizes fruits, vegetables, whole grains, legumes, soy, nuts, and seeds then it is a nutritionally sound diet. These foods are rich in disease fighting phytonutrients, fiber, vitamins, minerals, and water. All of these nutrients work together in our bodies to help prevent cancer, heart disease, type 2 diabetes, etc."

"Further, eating a diet varied in plant foods ensures a healthy gut microbiome, which is correlated to good health. I do believe supplementing with B-12 and DHA/EPA omega-3 fatty acids is warranted when following a vegan diet as these are nutrients found in animal foods. I realize that ALA omega-3 fatty acids from plant foods can be converted in the body, but not at the same success rate."

The Bottom Line

If the science does not back up claims in favor of a carnivore diet, why is it that people claim it helps them? It is likely from the removal of added sugars, alcohol, and ultra-processed foods and/or from the removal of a particular food that they are unknowingly sensitive to as a type of elimination diet.

Otherwise, the carnivore diet is not only unnecessary and overly restrictive, but also associated with many long-term health risks including heart disease, cancer, poor gut health, nutrient deficiencies, diabetes, and all-cause mortality.

Do you have to be fully vegan to reap the health benefits of plant foods? No. But I do want to stress the importance of the majority of your food coming from whole plant-based foods (like with the Mediterranean diet) for optimal health due to the fiber content, antioxidants, and anti-inflammatory compounds.

Extensive scientific research points to the health benefits of a predominantly plant-based and balanced diet, whether or not some minimally processed animal-based foods like dairy, poultry, or fish are included as well. If you need help following a high-protein diet without relying on as much animal-based protein, I have tons of resources on how to get enough protein from plant-based food sources.