Updated: Sep 20
High-Fat Diets in Human Health
A Summary of the Current Research
Introduction
The idea that eating a high-fat diet may help you lose weight, help lower blood sugar, give you more energy and help with food cravings – these are hot topics today in our society – no doubt! And while people ask themselves every day, “Is keto right for me?” what most people don’t ask themselves as an even better question is this: “Do I need to eat more healthy fats?” Not only for fat loss, but also, eating a high-fat diet may help you to train your body how to use fat for energy more easily! And while there are many people on either side of this argument, there exists very few summaries of the research over the past 70 years where high-fat diets have been talked about. This blog post aims to explain the data that is important in discovering how our bodies use fat from both our body AND our food! This research suggests that dietary fats play a large role in the improvement and optimization of human health and performance.
High Fat Diets
The Mediterranean Diet
By far, the most common researched high-fat diet is the Mediterranean Diet. This diet is defined by one particular study (1) mentioning foods such as:
Extra virgin olive oil (EVOO)
Vegetables including leafy green vegetables
Fruits
Cereals
Nuts
Pulses/legumes
Moderate intakes of fish and other meat
Dairy Products
Red wine
The Mediterranean diet was also identified in this review as being low in eggs and sweets.
While the body of research that involves the Mediterranean Diet is big, there have been a few pieces of research that have stood out to define the effects of the MedDiet in human health.
The PREDIMED Study – 2019
This study is, to this day, the largest diet change trial to study the effects of the Mediterranean Diet in humans. After it was published, it received scrutiny about whether or not it was controlled for randomization and was retracted in 2018. It was then republished in 2019 as non-randomized trial. This study looked at the effects of a high-fat, Mediterranean diet (extra olive oil, or nuts) and compared these people to the control group, who were told to reduce the amount of fat in their diet. No subjects were instructed to lower their calories. At the end of the almost 5 year study, those who were in the high-fat Mediterranean diet with olive oil group lost significantly more weight than the low-fat control group (2).
The DIRECT PLUS Study – 2021
In early 2021, the bmj journal “Gut” published a clinical trial by Meir et al that talked about their “Green Mediterranean Diet” and fatty liver(3). The Green Mediterranean Diet (also known as GMD) is like the Mediterranean diet – lots of olive oil, vegetables and nuts – but does not allow eating red meat and processed meats (such as pepperoni and salami) and adds in more green vegetables, walnuts and photonutrients called polyphenols. There were 3 groups in this study: The “Healthy Dietary Guidelines” control group, who received info on a healthful diet, the “Mediterranean Diet” group that was instructed to consume a lower-calorie Mediterranean diet, and the “Green Mediterranean Diet” group whom were also instructed to lower their calories on a Mediterranean diet with the addition of green tea, walnuts and a polyphenol shake. This was 3 cups of green tea per day, 28 grams of walnuts per day, and a daily shake that contained an plant known as Mankai. Both the control and the Mediterranean groups in this study did not receive any green tea, walnuts or polyphenols during the study.
After 18 months, liver fat (IHF) loss was measured in all groups. Although weight loss was similar in both the Mediterranean and Green Mediterranean subject groups, the Green Mediterranean group achieved almost double the amount of fatty liver loss based on their IHF results (down 19.6% IHF for the Mediterranean group vs down 38.9% IHF for the Green Mediterranean group) The control HDG group had a loss of 12.2% IHF showing that the Green Mediterranean Diet group was 3 times more successful in lowering fatty liver.
The PURE Study – 2017
This epidemiological cohort study observed the food intakes of more than 135,000 people in 18 different countries using food questionnaires (4). The results from this study show that while a high-carbohydrate diet did not increase in heart disease, a high-carb diet did increased the risk of death. Interestingly, total fat and the different types of food fats were related to lower death rates. Even more interestingly, saturated fat actually had an opposite effect on strokes! The important take away from this large-scale study is that total fat and types of fat were not associated with heart disease, heart attacks or death from heart disease.
The Ketogenic (Keto) Diet
Fasting is a practice that has been used as a therapy for thousands of years for epilepsy (5). In the early 1920s, before to the keto diet was made, doctors Cobb and Lennox used fasting (no food or energy) for 2-3 days for lowering seizures in epileptic patients. The ketogenic diet was created as a way to imitate the therapy-like effects of ketosis , a phase in the body during fasting where ketone bodies (what is left of fat breaking down to be used as energy) become higher in the body. Ketone bodies are used for energy instead of carbs and protein when their levels are high enough in the body. The keto diet became “better” than fasting for the reason that it didn’t cause as much weight loss in patients. A keto diet means eating a high amount of high-fat foods (70-80% or more of your total calories), a medium amount of protein (20-30% of your total calories), and very little carbs (less than 10% of your calories).
High fat foods in a keto diet can include:
Oils, such as olive oil, avocado oil, coconut oil and palm oil
Butter or ghee (a clarified butter traditionally used in Indian cuisine)
Avocados
High-fat nuts such as walnuts, pecans and macadamia nuts
Eggs
Meat, especially dark meat, meat with skin, and fattier cuts of meat such as a ribeye or shoulder
Bacon
Cheese, including hard cheeses, soft cheeses, cream cheese and sour cream
Salmon
Seeds such as hemp seeds and chia seeds
What Other Diseases Could the Keto Diet Potentially Help Treat?
Diabetes
In 2014, a tech-based weight loss company called Virta Health was created. According to their website, the company had a goal of “reversing type 2 diabetes in 100 million people by 2025” using a keto approach. In 2018, the Diabetes Therapy journal published a study on 218 people who participated in the Virta Health way (6). Changes in the group (CCI) included Continuous Care Intervention – which consisted of a medical exam, lab testing, a health coach, and one-on-one recommendations for achieving ketosis. This meant ketone body levels ranging from 0.5-3.0 mmol/L. After 1 year of study, the CCI group lowered their A1c by 17%. 85% of these CCI participants at the 1-year mark lowered their A1c by greater than 2.2 mmol/L each. Not only were diabetes numbers significantly lower, but these subjects also increased their HDL (good) cholesterol by 18%. Apolipoprotein B concentrations were unchanged by the end of the intervention. This study also measured a number of other labs and can be referenced at the bottom of this page or on the Virta Health website.
Possible Concerns Involving the Ketogenic Diet and Diabetes
While there have been many studies to show the good effects of the keto diet for diabetes, there are a number of things that should be thought about when considering this particular diet for diabetes. Of relevant, but less mainstreamed, concern is the effect of added nitrites and nitrates that are found in a number of foods that work with to a ketogenic diet. Sodium nitrite and sodium nitrate are chemicals that are added to foods such as cured meats, deli meats, sausages and bratwursts. Sodium nitrite and nitrate combine with amines and amides in these high-fat foods to form pro-cancer compounds called N-nitroso compounds(7). There is outdated research (1992) regarding clinical trails that certain fruits and vegetables may stop the formation of N-nitroso compounds from forming in the stomach(8). N-nitroso compounds have been shown to harm cells in the pancreas, where our insulin is made. Research associating these nitrites and nitrates to cancer in humans is lacking, although it has been reported that exposure to N-nitroso compounds in humans can occur via diet(9). A 2020 study showed an relationship between nitrates in drinking water and colorectal cancer(10). In 2021, the International Agency for Research on Cancer (IARC) under the World Health Organization (WHO) announced that the consumption of red meat and processed meat may affect the incidence of colorectal cancer(11). Also, an association with stomach cancer was also seen, but the evidence is not conclusive.
Obesity
Obesity in and of itself as a metabolic disease has been argued. Companies such as Health at Every Size (HAES) and the National Association to Acknowledge Fat Acceptance (NAAFA) are active in their efforts to increase body approval regardless of the amount of fat that is present in a human body. While these companies bring an important effort against bullying, the pro-inflammatory metabolic actions of excess fat remain a concern in the medical field(12). For example, in the field or orthopedic medicine, morbid obesity (a BMI of 40 or greater) has been shown to significantly increase the risk of multiple complications following lumbar surgery including the surgical wound breaking open and infection(13). Fat cells produce inflammation. We know this because they produce proteins called “cytokines” that are linked to inflammation. While a BMI of 40 or greater has been shown to be pro-inflammatory, there is actually very little data to suggest that a BMI of 25 (overweight) to 32 (obese) is related to an increased risk of complications following orthopedic surgery. This idea is compatible with the idea that weight loss for those who have an increased risk for disease and complications could benefit from weight loss to lower inflammation and improve their immune system for healing. While the research for the treatment of obesity (a BMI of 30 or greater) using a keto diet is plentiful, there is less data specifically for the treatment of morbid obesity (BMI of 40 or greater) with keto. More evidence is needed to explore the long-term outcomes of this possible intervention.
That being said, a valid concern with the keto diet (as with every other diet for weight loss) is the maintenance of weight loss following a diet. Ketogenic diets significantly restrict carbs, foods that exist in abundance in the traditional American diet, especially in highly processed forms such as bread, crackers, pastries, cookies, etc. In 1996, The American Heart Association stated that “The diet high in unsaturated fat (up to 35% calories from unsaturated fat plus up to 10% of calories of saturated fat) can be a viable alternative to a diet that is low in total fat” (14), which is why a high-fat, moderate protein, low carb diet may be advantageous for some individuals.
Advantages of the Ketogenic Diet for Weight Loss over Other Diets
When true ketosis happens during a ketogenic diet (ketone bodies that range from 0.5-3.0 mmol/L)(15), the body is able to use ketone bodies as energy for movement and life. Because ketosis uses fat for fuel, the process that usually makes energy in our bodies (Glycolysis) is impaired. Glycolysis uses carbs and protein for energy, ketosis uses fat. Therefore, what is called a “protein-sparing effect” happens in the body in ketosis – and this does not happen in glycolysis unless our protein needs are being met! Long story short, when someone is in ketosis, they are less likely to eat away their muscle tissue for energy and really direct that energy burn to fat! This can be extremely advantageous because most people want to get rid of fat (not muscle!) and calorie restriction diets that involve carbs, especially those that do not meet the person’s minimum protein needs such as in very low calorie diets, have been shown to result in some degree of muscle wasting(16).
Possible Concerns with the Ketogenic Diet and Weight Loss
A possible disadvantage of the ketogenic diet involves higher intensity exercise. Because ketosis is a state where the body is burning primarily fat for energy, when exercise intensities reach a threshold where carbohydrates become the main source of energy (at around 70% of VO2 max) metabolic adaptations occur in order for the body to increase its ability to use fat as energy at high intensities. Many people find it strenuous to work out at high intensities on a ketogenic diet and there is bountiful evidence that a ketogenic diet does not improve exercise performance in the immediate term(17, 18,19).
Another consideration for the keto diet is that ketosis becomes more difficult to achieve as metabolic adaptations take place over time – creating an environment where muscle tissue wasting is increasingly more possible. Traditionally, ketosis was achieved with prolonged fasting (for more than 24 hours). Strict doctor supervision with these types of dietary interventions are imperative. Using exogenous ketones (ketone bodies that you can take as a supplement) may help to keep ketone levels at a level where ketosis is possible. You should talk with a Registered Dietitian and get personalized advice when considering any of these interventions.
The Keto Diet and Cancer
It is important to note that the clinical trials which initiated a ketogenic diet in cancer patients did so in combination with conventional therapies including chemotherapy. In one pilot study in which the subjects were mice with pancreatic cancer, researchers were able to demonstrate that the keto diet increases radiation sensitivity, thereby perhaps increasing the effectiveness of chemo(20). In the following phase I clinical trial involving humans researchers were unable to complete the study due to too many human subjects being able to complete the trial duration due to non-compliance to a ketogenic diet. This is an important factor to acknowledge when considering the appropriateness of a ketogenic diet in cancer patients.
The Keto Diet and Alzheimer’s
Research involving the ketogenic diet and Alzheimer’s disease is very new in the field of science. Mice studies have been able to show that adherence to a ketogenic diet betters cognitive impairment and inflammation in the neurological system in those with Alzheimer’s disease (21). One human study was able to show that subjects with Alzheimer’s who adhered to the ketogenic diet improved their daily function and overall quality of life (22). It is apparent that much more research is needed in this field of study, but the preliminary data is exciting!
The Carnivore Diet/Modified Atkins
A newer diet trend that is emerging within the high-fat diet realm is the Carnivore Diet. The Carnivore Diet consists of meat and animal products such as eggs and dairy. It may also be considered similar to a Modified Atkins Diet from a macronutrient standpoint, as it is very high protein, high fat, and low carbohydrate. Naturally, it would not be considered ketogenic unless the amount of fat was at 75% or greater, which is unlikely although possible with a meat-based diet. If you want to talk about a field that is lacking in clinical trials, let’s talk about this one! We are in need of SO much more data regarding this topic and hopefully there will be more efforts in the future to achieve this. What we can discuss in this topic is the idea that pro-carnivore advocates make the argument that plant-based compounds, such as lectins and oxalates, may be pro-inflammatory to the body(23, 24).
Fats and Cardiovascular Disease – What the Decades of Literature Say
Now friends, I know you’re gonna hate me for this, but once I reached this point of my blog post I realized that this topic in and of itself warrants an ENTIRELY separate blog post because there is SO much information and so many different considerations with this topic! So, I love you all, but you are going to have to stay tuned for my next blog post on this topic!!!
Summary
While the topic of high-fat diets remains controversial with traditional/orthodox dietetics and nutritionists, it is clear that after reviewing the literature that high-fat diets when executed correctly are not only safe but also effective in lowering pro-inflammatory markers in the human body as well as in improving undesirable lab markers indicative for increased risk of diet-related disease. There are decades of clinical trial data that suggests plant-based fats such as olive oil, nuts and avocado are healthful foods that should be included in a person’s diet as tolerated. High-fat diets range from 35% up to 80% or more depending on the diet, and implore multiple metabolic mechanisms, including metabolic adaptations and ketosis.
A resource that some may find helpful in navigating literature-based evidence in favor of high-fat diets is the Weston A Price foundation, which can be found at https://www.westonaprice.org/
Resources
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Meir et al. Effect of green-Mediterranean diet on intrahepatic fat: the DIRECT PLUS randomised control trial
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