Nutritional Science: Carnivore Diet

Nutritional science is a messy, highly contested field that has an almost partisan dynamic as people pick a team to play for. There are many hills to die on, from vegan to carnivore and keto to slow-carb. The variety of diets out there seems to have grown exponentially, but it's more likely the case that heated debate over different diets has just increased exposure. Just like politics and clickbait, discord increases viewership. Today we will be talking about the carnivore diet, which has grown in popularity over the years. Recently, notable (and sometimes controversial) people like Joe Rogan, Jordan Peterson, Paul Saladino, and Mark Bell have touted its benefits online while others say it's slowly killing people. Before you read on, please note that this is not medical advice, and I am not arguing for OR against utilizing the carnivore diet.

Let's first talk about what the carnivore diet even is. To put it simply, the diet requires the consumer to rely solely on animal products as a means of nutrition. The strictest form of the diet is meat and water, that's it. Other forms of the diet include items like eggs, cheese, bone broth, and butter. There is a lot of debate about what types of meat should be consumed, whether supplementation should be used, and if this diet is even healthy in the first place. Generally speaking, red meats are relied on heavily due to an increased percentage of fat. Since carnivore is essentially a zero carbohydrate diet, relying on fat is essential for energy. Pretty much all tissues in your body can use fatty acids as an energy source (most notably cardiac tissue), but they cannot cross the blood-brain barrier meaning that your brain cannot utilize them. Fortunately, when glucose and insulin levels are low, fatty acids are made into ketones which the brain can use for energy. So in essence, the carnivore diet is a subtype of the ketogenic diet. Ketogenic diets inherently tend to decrease blood glucose and increase insulin sensitivity which is why they are often studied in diabetic patients. Whether or not the carnivore diet is healthy is probably dependent on the individual. I have personally been on the carnivore diet twice in my life, each time being on the diet for 1 month. Both times I performed this nutritional experiment I was joined by my father-in-law, and as I point out in my post on How to Utilize Group Studying in College it is much easier to do something like this when you have someone else to hold you accountable.

Curious as I was and cursed with needing actual metrics to make personal decisions on safety and efficacy, I had a lipid panel taken at the end of April 2020 ("Carnivore April") to see how much the diet would affect my total cholesterol, LDL, HDL, and triglyceride levels as well as my cholesterol:HDL ratio. My results can be seen below:

Triglycerides: 48 mg/dL; Cholesterol: 144 mg/dL; HDL-C: 49 mg/dL; LDL-C (calculated): 85 mg/dL; Cholesterol/HDL-C: 2.9

If you are unfamiliar with these biomarkers, let me provide some background. Triglycerides are esters formed from glycerol and 3 fatty acids (hence the name triglyceride), which many people just think of as "fat". Having high energy levels in your blood, whether that be triglycerides or glucose, is generally considered a bad sign. Such is the case with high blood glucose (hyperglycemia) and diabetes. Cholesterol can be consumed or created and is essential for you to stay alive. The cholesterol that you consume is mostly esterified cholesterol, which is not largely absorbed into your blood. Therefore, most of the cholesterol in your body was made by your body. HDL, LDL, and VLDL are lipoproteins (high density, low density, and very low density respectively), which carry triglycerides, cholesterol, and fat-soluble vitamins around your body. LDL-C and HDL-C refer to the cholesterol being carried by LDL and HDL respectively. Lipoproteins rely on apoproteins to interact with cells. The major apoproteins are the apoB class (which you'll find on LDL and VLDL) and the apoA-I class (which you'll find on HDL). To confuse matters further, "LDL" is generally referring to LDL-C, not the number of LDL particles (LDL-P) which is known to be a better predictor of cardiovascular disease (see here). I can tell you that all of my results are well within normal limits and are actually quite good according to a traditional understanding of triglycerides and cholesterol. It's been documented before that triglyceride and cholesterol levels can actually decrease on high-fat, low-carb diets (see one paper here). Alternatively, this paper reports that triglycerides decrease but HDL (meaning HDL-C) and LDL (meaning LDL-C) increase at varying levels depending on diabetic status. Then we have this paper, which was conducted on patients with known atherosclerotic disease and on a statin that resulted in decreased plasma triglycerides and VLDL triglycerides, no change in LDL-C or LDL-P, decreased fasting glucose and insulin, and decreased triglyceride:HDL-C ratios (note that use of a statin likely makes it impossible to assess the diet's effect on LDL). I realize that I don't have my own levels to compare to before the diet, and fully understand this to be a deficiency in my data. Also, keep in mind that this is an example of N-of-1 self-experimentation and may have very little relevance to others.

As for my weight, I can report that I did lose roughly 15 pounds throughout the month. However, the percentage of weight loss attributable to water, fat, and muscle is up in the air. I suspect that a lot of it was water weight, especially considering ketogenic diets have a well-documented diuresis effect. In fact, ketogenic diets have been shown to cause weight loss much faster than more traditional low-fat diets, likely due to enhanced water loss. The difference in total weight loss between diets tends to disappear over time. What really matters is the simple formula of (calories in) - (calories out). If you get a negative number, meaning that you burn more calories than you consume, then you will lose weight. It's that simple. You can achieve this by exercising more, eating less, or both. As to what you are eating, it doesn't really matter if we're strictly looking at pounds lost. Supporters of high-fat diets will tell you that they feel fuller for longer and therefore find the eating less proponent easier to handle. Personally, I tend to agree.

The debate comes in when looking at things like cholesterol, heart disease, cancer, and diabetes as adverse effects of dietary manipulation. Supporters of ketogenic diets will point the finger at hyperinsulinemia, hyperglycemia, and inflammation as the driving forces to such adverse events. As Peter Attia, MD points out in his incredible series on cholesterol, "It is entirely plausible that an elevated level of LDL-P or apoB in someone consuming a high-carb diet portends a greater risk than someone on a ketogenic or low-carb diet." This goes against the conventional claims of the famous Framingham Heart Study, but only time will tell the truth as we further explore this topic. Has the carnivore diet ever been proven inferior through a well-run, prospective clinical trial that properly controls for confounders and ensures compliance to the dietary regimen? No. Have there been studies that try to answer the questions regarding meat consumption and the potential benefits and cons? Absolutely. But as I've said, these studies are full of confounding variables, reliance on patient reporting (which is really subjective data rather than objective), bias, and controversy. For instance, many studies showing that red meat consumption increases the risk of cancer do not control for sugar or processed carbohydrate intake. They also rely on patient questionnaires that, in some cases, are sent to subjects annually (and sometimes longer). In such a study, every patient consuming red meat could therefore be eating it with a side of mashed potatoes and a large coke. They'd also be expected to have a clear idea of their eating habits over the past year. I can't even remember what I had for breakfast last Tuesday. Here is one very large and famous study claiming to strengthen the evidence that long-term red meat consumption is associated with colorectal cancer, but just by taking a look at the conclusions section of the abstract you can quickly see that findings in this area are very controversial and have no real consensus. Some studies will adjust for fiber intake, but what if the real problem is high-fat foods and red meats combined with processed carbohydrates? We just don't know. Not to mention, for every study supporting someone's (or your, or my) point of view, there is a study that refutes it. For example, here is a paper about the effects of red meat consumption on cardiometabolic and cancer outcomes, and here is a dietary guideline from the Nutritional Recommendations (NutriRECS) Consortium. Both papers suggest that diets restricted in red meat may have little or no effect on cardiometabolic or cancer outcomes and that patients should continue their current level of meat consumption. Now, here is an article saying that the first 2 papers are wrong, dangerous, and harm the credibility of nutritional science, and then we have this article saying that the Annals of Internal Medicine (the journal where the first 2 papers were published), faced massive blowback for the studies before they were even published. What is one to think about all of this? For me it's simple. No one knows for sure, and if they tell you so they have simply convinced themselves and ignored or written off contradictory evidence. That last sentence is obviously my opinion, but the point is that the perfect studies haven't been done, partly because it would be incredibly expensive to perform a long-term study that provides food to all of its subjects and can ensure compliance. Then there's the ethical dilemma of long-term studies evaluating diets that could certainly turn out to be harmful. I could not confidently tell you whether the vegan, ketogenic, vertical, vegetarian, low-fat, high-carb, slow-carb, carnivore, or IIFYM diet is better or worse for you. Of course, I have my suspicions and thoughts about what diets make the most sense. Overall, my approach is to try them all, see how I feel, and pick what is right for me. I hypothesize that people vary too much genetically and culturally for a broad sweeping recommendation to be made. In the end, the best diet is one you can follow consistently while staying active and happy. We may be overcomplicating things anyways. Perhaps the best way to tell whether your diet is healthy is simply by looking in the mirror, stepping on a scale, and appraising how you feel.  

Speaking of picking a diet that you can follow consistently, the carnivore diet is not that diet for me. However, I split my experience into positives and negatives.

Positives: I enjoyed challenging myself with carnivore, benefiting from the weight loss, and seeing how I felt. Compared to all of the diets I have tried, and there are many, carnivore kept me feeling full the longest and was probably the easiest to lose weight on. I did not count calories, macronutrients, or weigh my food in any way. It's also a rare case that you can eat brisket and bacon without worrying about weight gain. I found grocery shopping to be much simpler as I really only visited one section. Importantly, I enjoyed the experience of dropping bodyweight while getting stronger in the gym, finally hitting 315lbs on the bench press which was a lifetime goal for me. This is important to me because my diet is often meant to enhance performance rather than weight loss. I also appreciate the thought of being metabolically flexible, which is a topic for another time. Mentally, I didn't feel much different than I would on any other diet. Supporters of carnivore and ketogenic diets often report increased mental clarity, but this wasn't the case for me. You'll also hear that elimination diets, including carnivore, often solve issues related to autoimmune disorders, depression, and injury. These benefits are strictly anecdotal, but you do see them as common themes when listening to content creators like Paul Saladino, MD, Jordan Peterson, Ph.D., and communities online. I was not dealing with any of these issues when I started the diet, so I cannot provide any input on those benefits specifically. I also really started to enjoy the process of cooking and preparing my food. I definitely got better at grilling and cooking steaks, but I also just loved spending time outside with the smoke of the grill around me. We even made caveman steaks (also known as dirty steaks, fire steaks, or Eisenhower steaks) for the whole family which involved cooking thick ribeyes directly on the coals of a fire. You just brush off the coals when they're done, and they turn out great.

Negatives: The diet can definitely become dull over time, and if you don't have the diligence to stay on it you're likely setting yourself up for worse outcomes. Doing the carnivore or ketogenic diets half-heartedly while eating bread, pasta, and chips is the same thing as being on the SAD diet (standard American diet), which is universally thought to be bad for you. Some people, including myself, experience gastrointestinal issues at some point in the diet, and others dislike the lack of variety. Personally, I just missed eating other things like fruits and vegetables to add some variation to my meals. People will often complain about the personal costs of the carnivore diet and that it can be hard to afford. Admittedly, this could be the case for any diet depending on your financial status. However, I do agree that this could be a major con if you are eating ribeye steaks every night for dinner. I was able to find much cheaper alternatives like ground beef, frozen salmon, marinated chicken, sausage, brats, and a lot of bacon and eggs. I was also very lucky that my father-in-law occasionally splurged on brisket and was generous enough to share.

Would I try the diet again? Potentially. I really loved the challenge and benefits of the diet, but I might stick with a standard ketogenic diet which could easily be done more long-term due to increased variety.

OPINION: I wanted to close with some personal thoughts on nutritional science and modern medicine. As I've said, research in this field is extremely messy with innumerable confounding variables, mostly retrospective data, and extreme bias by authors. Aside from these shortcomings, there has been a massive shift in medicine over time towards large clinical trials with thousands of patients as the main means for coming up with treatment guidelines. Ultimately, I view this shift as a huge positive which has certainly led to better patient outcomes and saved thousands of lives. However, one personal worry is that fully relying on this system leads to decreased consideration of the individual. You will oftentimes see providers following guideline recommendations that were derived from studies of patients that look nothing like the patient they are treating. There are some shocking examples of this like making weight loss recommendations based on the BMI scale, which if applied without considering the individual patient can be ludicrous. For example, Matt Frazer, 5-time CrossFit Games Champion and therefore titled "The Fittest Man on Earth" would be considered obese with a BMI of roughly 31.5 kg/m^2. One google search and a quick look at his physique will promptly show you how crazy that is. I fear similar misgivings with diet recommendations. If you look at the patients who experience heart attacks due to hypercholesterolemia, they are also likely dealing with comorbidities like diabetes, hypertension, and obesity. Do we really know the dangers of cholesterol in an otherwise healthy individual, especially one without those highly inflammatory diseases or on a unique diet? There are ultra-marathon runners on the ketogenic diet; are we going to look at their lipid panel and suggest that some of the most cardiovascularly fit people on earth are at risk of a heart attack? Can we accurately weigh the risks and benefits of increased cholesterol vs increased insulin sensitivity and decreased blood sugar in a diabetic on a ketogenic diet? I don't think so. A potential safeguard is for doctors to start "doctoring" meaning to evaluate the patient as an individual and really consider if guidelines accurately apply. Remember, for every 95% confidence interval with statistically significant p-values, some patients were outliers, responded inversely to the study's overall conclusion, or had confounders that couldn't be adjusted for. We just need to keep that in mind when treating patients that don't respond the way we expected because we read one meta-analysis or memorized a guideline. Not to mention, that guideline is going to say something different every year!

DISCLAIMER: This topic is massive, and this post does not come anywhere near being comprehensive. Many variables have been left out here ranging from genetics and study appraisal to economics, ethics, and carbon footprints. Please follow the advice of your doctor when it comes to your own health.