Does the thought of eating steak for breakfast, lunch, and dinner make your mouth water? Or does it make your stomach turn? Many of my colleagues and folks in the paleo keto community are trying and touting the all-meat, zero carb carnivore diet, so of course I was compelled to dive into any research to examine the benefits and risks involved. While I strive to present an unbiased look at diet fads by letting you know the pros and cons, I of course have my own opinions that I will share.

What we eat has an incredible impact on our health. For example, your diet has the ability to prevent or contribute to disease and inflammation. And certain diets, like the ketogenic diet, even have physiological effects as powerful as prescription meds. (Side note: Please check out my post on the pros and cons of keto if you want a closer look at benefits and risks, and don’t forget to check out the comment section to see just how passionate people are about this diet, facts or not).

What is the Carnivore Diet?

The rules are simple for the carnivore diet: Eat only meat, organ meats, seafood, bone broth, and eggs (optional). No plants. Nothing else. Just meat. Some people drink coffee, use butter and cream, or include cheese. Others are purists, even limiting spices and using only animal fats. Vegetables, grains, nuts, seeds, fruit, alcohol, or anything else not meat related is off limits.

Here’s an example day’s meal plan for carnivores

• Breakfast: Ground beef and coffee (some people include bacon) or eggs
• Lunch: Rib eye topped with grass fed butter
• Dinner: Lamb or shrimp and salmon filet
• Optional Supplements: sea salt, minerals, electrolytes, perhaps a multi to cover the bases for all the nutrients you cannot obtain from meat; however, some discourage supplement use.
• Booster foods include organ meats, bone broth, roe (fish eggs)

Carnivore Diet Benefits

Meat does offer an array of nutrients like B vitamins, vitamin A, iron, amino acids, fatty acids, zinc, and some minerals (especially shellfish, which is high in iodine). At this point, all we have are anecdotal evidence reports from people, both positive and negative, because we haven’t studied nor have long term data about an all meat diet. That doesn’t mean it is without benefit, but it’s instructive to know that you are a guinea pig in this particular diet experiment should you choose to make it a long term lifestyle.

Carnivore benefits reported include the following

• reduction or remission of autoimmune conditions
• better energy and sleep
• pain reduction
• weight loss
• inflammation reduction (in certain individuals)
• improved cognition
• reduction in bloating and nagging digestive symptoms

One reason this diet may offer such relief to those with chronic health issues is that it excludes foods that trigger inflammation or adverse reactions in people with autoimmune issues, chronic pain, and/or inflammation. The foods most likely to trigger reactions include dairy, nuts, legumes, grains, eggs, and even certain vegetables like nightshades. It’s basically an extreme elimination diet. 

Hormesis

Believe it or not, plants contain phytochemicals that act as natural pesticides to dissuade consumption by predators (see The Plant Paradox and my blog post on lectins). These “anti-nutrients” are designed to poison or kill predators so the plant can remain alive. In most humans, these phytochemicals act as hormetic stressors that make us stronger, healthier, and more robust. That means they will irritate us enough to induce a compensatory adaptive response that results in many health benefits. Exercise is another form of hormesis. In other words, both exercise and brightly colored fruits and vegetables stress the body in a way that produces a response that is beneficial to health.

Some of the most common problematic vegetables are nightshades, which are high in lectins. One theory about why the carnivore diet offers people with autoimmune disease or chronic pain so much relief is because lectins and anti-nutrients in certain vegetables may aggravate their autoimmune conditions and contribute to flares. Certain bodies, therefore, may react adversely to plant foods rather than reaping the hormetic benefits. That’s probably the reason that people with autoimmune diseases chronic GI conditions see a lot of relief and inflammation reduction eating only meat, at least initially.

Another main argument I see in favor of an all meat diet is that many tribes throughout history thrived eating only meat, fat, and blood. This is misleading. First off, we don’t know 100% if there have been any purely carnivorous cultures. (source) And secondly, if your close ancestors weren’t carnivores, you might not have the genetic adaptations necessary to thrive on an all-meat diet.

We fare best eating according to our ethnicity, and it’s a bit myopic to assume that just because ancient tribes on different continents than you that eat meat and fat (and hunt and move throughout the day and weren’t exposed to modern pollution or chemicals) had lower disease markers that modern humans or all ethnicities will also. So if you are not an Eskimo or from Mongolia or East Africa (where many of these tribes exist or may have existed), you probably don’t or may not have the genetic makeup that supports this type of diet.

Carnivore Diet Negatives

The all-meat diet is zero carb if done without dairy products, still minimal carb if you do include dairy. You might be thinking that because it’s so low carb, it must throw you into ketosis, and you’ll reap the benefits of a ketogenic diet (which vary per individual). But the carnivore diet includes too much protein to be a true ketogenic diet. When the body takes in more protein than it needs, the excess is disposed of through the liver and also by a process known as gluconeogenesis, where protein is converted by the body into glucose. The process of gluconeogenesis is what prevents carnivore people from reaping the benefits of ketosis.

Here’s the deal: the carnivore diet that is beneficial to you mostly comes down to genetics. It’s why some people thrive on high fat diets, whereas others may experience a spike in inflammation, putting them at risk for heart disease, if they eat keto or high fat. We’re not all adapted to eat a ton of fat or even a lot of meat.

For example, a well known concern about high protein diets is kidney and liver damage. When we eat protein, the body breaks down the nitrogen molecules and turns them into ammonia, which is then processed by the liver into urea, which goes through the kidneys on its way out of the body as urine. (urea cycle). People with genetic variants in the urea cycle pathway (which are common, 33% of people have at least one copy of the risk allele for CPS1) will have major problems on the carnivore diet. Ammonia, a known neurotoxin, will pool in their body, leading to a range of different health problems over time. (source)

So there’s a genetic component to who may thrive on a carnivore diet. Fortunately you can map your genome via genetic testing to find out if your genes like a lot of protein or not.

Long Term Concerns with Carnivore

Aside from that, the main concern with a long term carnivore diet (longer than 2-3 months) is the lack of fiber that provides food and nourishment to the trillions of bacteria in our large intestine. These bacteria help us digest food, prevent disease, modulate inflammation, and manufacture certain vitamins. A fiberless diet wreaks havoc on the ecosystem in our colons (our microbiome). “Growing evidence suggests that in the absence of adequate fiber, the bacteria in the colon consume and thin the protective mucus lining, which then leads to impaired immune function and inflammation.” (source) A thriving, diverse and balanced microbiome is just not presence in the absence of dietary fiber.

You can’t properly feed your microbiome with meat, because plant foods contribute to the robust probiotic environment that keeps you healthy. The majority of your immune system is in your gut, so it’s vital to make sure those populations thrive. Starving them = lower probiotic diversity, which could cause inflammation, leaky gut, and lowered immune response down the line. The one mild counterpoint to this is that meat does contain a shitload of amino acids that your gut lining needs to repair itself.

You can–and absolutely should–purchase a gut test that assesses your bacterial diversity if you intend on doing carnivore longer than a couple months. Try Viome.

Another major concern is that an all meat diet may turn on cancer pathways in the body (again, in some people) by increasing levels of a hormone known as insulin like growth factor one, or IGF-1. (source) One of the world’s leading researchers on longevity has found that “protein restriction has been associated with reduced cancer, diabetes, and overall mortality. Thus, interventions aimed at lowering the intake of proteins or specific amino acids can be beneficial…” (source) Also, a diet high in meat amino acids tryptophan, cysteine, and methionine in particular is shown to increase aging and cancer risk.

For what it’s worth, studies on populations who live longest (those in the Blue Zones) share a major theme: They all have plant-based and diverse diets (that doesn’t mean they don’t eat meat; they just don’t eat a lot of it, or tend towards seafood). So there is a benefit for most people to eating a lot of plants. For optimal gut health and overall disease-prevention, I recommend a Mediterranean type diet with lots of veggies, healthy fats, nuts, legumes if tolerated, seafood, occasional red meat, low glycemic fruits.

Additionally, cooked meat (especially well done or grilled) forms chemicals called heterocyclic amines and polycyclic aromatic hydrocarbons that cause cancer. You can mitigate this risk by not cooking the shit out of your meat OR by eating lots of brightly colored fruits and vegetables that provide you with antioxidants to counter the free radical damage that causes cancer. (source)

Other Carnivore Concerns

There are just some nutrients you cannot obtain from meat. Folate, certain minerals, and vitamins C and E, for example, pretty much only come from veggies. You’re also missing out on certain vitamin co-factors that are necessary for other nutrients to do their jobs in your body. Anyway, you’re setting yourself up for deficiencies, and worst of all, robbing yourself of critical antioxidants you need to prevent disease.

Finally, a main concern about eating all that meat and fat is cardiovascular disease (CVD). While we do know that meat and fat don’t cause heart disease outright, high levels of saturated fat absolutely can cause inflammation (which raises cholesterol) in certain individuals who don’t process large amounts of fat well (again, you can find out of this is you via genetic testing, or monitor your blood work regularly). Remember, one man’s superfood is another man’s poison. Many times, in an all meat diet, blood cholesterol levels rise quickly. High cholesterol may not cause heart disease directly, but it DOES indicate inflammation, which causes CVD. While CVD risks don’t rise in a matter of months, it’s a concern long term.

Oh, and an all meat diet causes constipation in many people. You can probably guess why.

IMPORTANT TO NOTE: If you try this diet, you MUST use grass fed or organic meats and wild seafood. Conventionally raised grain fed beef contains antibiotics and hormones and an altered fatty acid composition that contributes to inflammation. In certain people, beef may be a food allergen which would cause inflammation, organic or not. That’s not as common as egg or shellfish allergies, however.

Who Should Try an All Meat Carnivore Diet

I rarely recommend extreme diets due to the potential risks involved and problems with compliance, but I have recommended an all-meat diet to certain clients with severe IBD or GI disease, and to those with chronic diarrhea associated with SIBO. It may also be therapeutic for those with autoimmune disease who experience regular flares or can’t find a way to decrease antibodies.

And I have seen several people experience great relief doing carnivore, mostly from inflammatory digestive conditions and autoimmune flares.

I’d recommend the carnivore diet for 2-3 months until the person experiences remission, then we can start adding back in some of the milder (nightshade free) veggies to identify triggers. This process must be done slowly and deliberately so you can tell which foods or classes of foods cause symptom flares, AND you should work on healing your gut simultaneously.

If you’re doing strict carnivore because you’re experiencing adverse reactions to even very small amounts of plant foods, that’s likely a sign of an underlying gut imbalance that should be addressed. Once your gut health improves, you should be able to tolerate more plant foods over time.

See my post on the elimination diet for food reintroduction directions.

This diet may work well for metabolic syndrome (high blood pressure, high blood glucose, overweight), but I’d recommend keto over carnivore for that.

If you do try a carnivore diet, you MUST monitor your blood work every few months to make sure it’s not causing inflammation or raising disease risk for you. Request the following markers:

• LDL and HDL cholesterol
• LDL-P – number one predictor of heart disease
• APOB – protein that makes up LDL particles
• sdLDL-C – small dense LDL cholesterol mass
• LDL-C – cholesterol mass within LDL
• C reactive protein – increases if there’s inflammation
• Serum ammonia – toxic byproduct of protein metabolism disposed of via the urea cycle
• Fasting glucose – level of blood sugar in the blood when not eating
• Lp(a) – unique kind of lipoprotein that puts people at higher risk for heart disease
• Homocysteine – common amino acid in blood associated with heart disease

Also note that the transition period can be very unpleasant (similar to the keto flu), lasting 7-10 days, and if it does trigger brain fog, malaise, or flu-like symptoms, you need to add sea salt to your water for additional electrolytes.

Who Should NOT Try an All Meat Diet

If you’ve done genetic testing and know you don’t do well with high protein or high fat diets, this isn’t the diet for you. That said, it probably won’t hurt to do it for a couple months.

If you have adrenal fatigue or hypothyroidism, use caution. I have, however, seen antibodies associated with Hashimoto’s autoimmune thyroiditis decrease on a 2-month carnivore plan.

If you have high iron, ferritin or kidney or liver disease, avoid.

Bottom Line

My major concern with this diet is the extreme restriction and potential damage to your microbiome. We don’t have long term data about all meat diets. And some, maybe even most, of us aren’t a genetic fit for this diet, meaning it can raise your disease risk. Any diet that supports eating only one thing– even only plants!– can be problematic because you’re just not getting the array of nutrients you need to thrive. It’s fairly astounding the number of nutrients your body needs to keep you healthy.

That said, I think it can be very therapeutic to those fighting SIBO, Crohn’s, or autoimmune diseases when used for a period of months. If you do try this diet longer term, make sure to monitor your blood work and gut function (via stool testing for bacterial diversity) every few months, or make it a temporary (3 months max) experiment.

Have you tried an all meat diet? What was your experience? Please share.

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Mary Vance, NC

Mary Vance is a Certified Nutrition Consultant and author specializing in digestive health. She combines a science-based approach with natural therapies to rebalance the body. In addition to her 1:1 coaching, she offers courses to help you heal your gut and improve your health. Mary lives in San Francisco and Lake Tahoe in Northern California. Read more about her coaching practice here and her background here.

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