The Paleo Diet and Coronary Heart Disease
Jack M. Wolfson, DO, FACC
Ashley Swanson, MS
“Whatever is Contrary to Nature Cannot Be Fact.”
Animals in the wild eat foods that are native to them. Lions, tigers, giraffes, baboons, and all animals, evolved over millions of years on a steady diet that is best summarized as hunter-gatherer. All animals are hunter-gatherers. All animals eat plant material. All animals eat other animals, seafood, and/or insects.
Nature needs no instruction and needs no input from the U.S. Department of Agriculture (USDA). Why should humans be any different? Why must we deliberate over what the best nutrition is for a man or woman? Baby humans enjoy the best health when they consume human milk. This is just common sense. The Paleo diet makes common sense. All societies in the history of the world ate meat, seafood, insects, or a combination thereof.
What Is the Paleo Diet?
In general terms, the Paleo diet refers to foods available to our ancient ancestors. Our ancestors were all hunter-gatherers. They would hunt animals, seafood, and insects. They would gather vegetables, fruit, tubers, nuts, seeds, and eggs. Foods not on our ancestral diet include cereal grains, such as wheat, oats, soy, corn, and other grasses, dairy, and sugar (aside from raw honey).
The word Paleo comes from the Greek word palaios, meaning “ancient.” Paleolithic refers to a period of time before recorded history starting around 3 million years ago with the earliest use of stone tools and ending around 12,000 years ago with the advent of farming.
The word Paleo in reference to a diet has been used interchangeably with Caveman, Hunter-Gatherer, Primal, and Ancestral. Most would say that a Paleo diet falls more toward the “low-carb” side with higher consumption of fats and proteins. All would agree that Paleo foods are not processed and exist in their natural form.
There are modern societies of Paleo eaters, but their numbers are small. Explorers from Cook to Magellan documented the food selection of prehistoric man. Weston A. Price, a dentist from the early part of the 20th century, traveled around the world by boat with his wife. He documented the ill effects on human health for those who suffered from poor dentition, development disorders, and childhood disease.
Clearly, different populations around the world consume different Paleo foods. What Paleo food is available to islanders in the South Pacific is clearly different from that available to an Eskimo in Canada or an African Hadza tribesman.
Two modern TV shows seem to epitomize what life was like in the Paleolithic time period: Survivor and Naked and Afraid. In each program, human contestants are living off the land as hunter-gatherers. They are in a perpetual quest for shelter and food. But the food they are searching for is not plant material. There is plenty of greenery around them. They are searching for animal and seafood. Finding such is always a cause for celebration.
The 1950s and a New Diet Paradigm
Medical doctors, researchers, and epidemiologists realized that there was a dramatic rise in chronic diseases in the United States and in developed countries around the world. Morbidity and mortality from infectious diseases were dramatically reduced with the improvement in sanitation, access to clean water, and plentiful availability of food. People were now living longer in an industrialized society, but easy access to food would prove to be a double-edged sword.
Caloric intake was much higher in the 1900s than ever before. White flour, white sugar, and white rice provided a massive spike in caloric intake, with little nutritional value. Obesity was rampant and myocardial infarction, stroke, and cancer rates were exploding. There were many key people in what can only be described as a low fat, high carbohydrate revolution. But there was no bigger persona than Dr Ancel Keys.
Ancel Keys was apparently a brilliant man with a wide scope of interests and scientific degrees. He researched the effects of starvation on prisoners of war and eventually on “conscientious deserters” from war. He developed the food protocols for military personnel known as the K-ration. Eventually his research would lead him to believe cholesterol and saturated fat were the villains in the story of human health. Ultimately, Keys would publish his Diet-Lipid Heart Disease Hypothesis and lead a massive study known as the Seven Countries Study.1 In short, foods rich in cholesterol and fats were condemned. Keys himself was a huge promoter of the Mediterranean diet and described his personal diet in a 1961 Time magazine article as “fish, chicken, calves’ liver, Canadian bacon, Italian food, Chinese food, supplemented by fresh fruits, vegetables and casseroles.”2
Keys and others in the low saturated fat camp would heavily influence US dietary guidelines in the 1970s that would culminate in the USDA Food Pyramid and other documents promoting the limitation of animal fats in favor of high-carbohydrate choices. Critics of the Seven Countries Study would point to the fact that Keys selected only seven countries to fit with his hypothesis. He excluded countries such as France, known to consume high amounts of saturated fats but with low cardiac morbidity and mortality, the so-called French Paradox. There is no paradox. Fat is not the problem.
Low Carb Fights Back
Not all doctors and nutrition authorities agreed with Ancel Keys. In fact, many outright disagreed. One of the most vocal critics of Keys dietary observation was Dr John Yudkin. He published a book in 1958 called This Slimming Business that blamed the current rise of cardiovascular disease on sugar. A movie based on his work was released in 1972, Pure, White, and Deadly. Yudkin had a different take from Keys on the increased incidence of cardiovascular disease and other chronic health conditions. He found that the increase in sugar consumption correlated with the alarming increase of myocardial infarctions in many countries during the first half of the 20th century. In a paper published in 1957,3 Yudkin analyzed diets and coronary mortality in different countries for the year 1952 and also analyzed trends in diet, and trends in coronary mortality, in the United Kingdom between 1928 and 1954. His conclusion produced no evidence for the view that total fat, or animal fat, or hydrogenated fat was the direct cause of coronary thrombosis. Yudkin thought it was all from sugar.
There were many other contemporaries critical of the work of Ancel Keys, including Dr George Mann, Thomas Cleave, George Campbell, and Edward Ahrens, Jr. Then, in the 1970s, a radical dietary recommendation was espoused by Dr Robert Atkins, MD. In 1972, Atkins’ book titled Dr Atkins’ Diet Revolution was published. In his book, Atkins pushed for a low-carbohydrate, high-fat diet. His theories led to a generation of physicians, PhD’s, and nutritionists promoting a high-fat, low-carbohydrate dietary plan. Ironically, Atkins died in 2003 from an intracranial bleed he suffered after a slip and fall on a patch of ice.
Paleo Reemerges As a Modern Dietary Recommendation
Dr Walter L. Voegtlin argues on the side of high fat, low carbohydrate in his book The Stone Age Diet, published in 1975.4 Voegtlin was a gastroenterologist and asserted that humans are mostly carnivorous animals. The Stone Age diet was that of a carnivore—chiefly fats and protein, with only small amounts of carbohydrates. He notes that, like the carnivorous dog, man has canine teeth, ridged molars, and incisors in both jaws. His jaw is designed for crushing and tearing as it moves in vertical motions. His stomach holds two quarts, empties in three hours, rests between meals, lacks bacteria and protozoa, secretes large quantities of hydrochloric acid, and does not digest cellulose. His digestive tract is short relative to body length, his cecum is nonfunctional, and his appendix vestigial. His rectum is small, contains putrefactive bacterial flora, and does not contribute to the digestive process. The volume of feces is small; digestive efficiency borders on 100%. The gallbladder is an organ with one purpose: the digestion of fat. The above-mentioned fact is obviously in contrast to a cow, sheep, or any other ruminant animal.
S. Boyd Eaton, MD wrote an article in the New England Journal of Medicine in 1985 espousing the health benefits of Paleo nutrition.5 Eaton graduated at the top of his class from Harvard Medical School and would practice radiology for 41 years. His book Paleolithic Prescription was released in 1988. The year 1999 saw the release of Neander-thin by Ray Audette, and then in 2001, Loren Cordain, a professor at Colorado State University, published his book titled The Paleo Diet: Lose Weight and Get Healthy by Eating the Food You Were Designed to Eat. With this publication, millions of people became Paleo acolytes. Paleo was recognized as our ancestral and evolutionary diet complete with macro- and micronutrients to optimize health and longevity.
Cordain and Eaton coauthored a paper published in the American Journal of Clinical Nutrition in 2000. They studied 229 different hunter-gatherer groups and found that, on average, two-thirds of net energy consumption was from animal foods, the other third coming from plants.6 Many sources including Eaton and Weston A. Price document extraordinary health in these hunter-gatherer populations.
Paleo Proof
In the following sections, I will make the case that Paleo nutrition, the diet humans have consumed for millions of years, is the best food plan for optimal cardiovascular health and longevity. Finding evidence for what appears to be common sense is not easy.
Let us face it, there are not many people eating the way Voegtlin recommends.
At this point, I would like to discuss the difficulty with nutritional scientific study. Reviewing the literature as it pertains to Paleo nutrition reveals the paucity of quality data in randomized trials. The following represents the issues that
continue to cause such debate among professionals and public alike in the dietary arena.
continue to cause such debate among professionals and public alike in the dietary arena.
Randomized trials to assess long-term results are fraught with difficulty. It is difficult for a study group to stay on a recommended diet and even more difficult for researchers to account for study adherence.
Epidemiological and observational studies have substantial flaws, including the difficulty in accounting for possible confounding factors. For example, a group identified as eating less red meat may also smoke less, exercise more, and experience less stress. All of these are other factors known to be linked to cardiovascular risk.
Food surveys are imprecise. This method of research includes dietary recall to generate data points and is notoriously fraught with error.
Conflicts of interest are rampant in research. Suffice to say that just about every researcher has conflicts, including how studies are funded or personal bias.
Animal data do not necessarily apply to humans. For example, many cardiovascular studies are done on the rodent model. Rodents may be easy to study, but the applicability of the results to human is imprecise. Rodents in the wild eat a diet high in plant matter; therefore, feeding studies high in animal fat, animal protein, and cholesterol may not have much value.
All foods cannot be considered equal. Evidence shows that the nutritional makeup of pasture-raised animals differ from that of grain-fed, confined animals. Omega-3 ratios, fat, and other nutrient content differ.7 Organic produce is different from pesticide and genetically modified plant materials. Wild seafood is nutritionally different from farm-raised fish.175
What exactly are Paleo foods, and in what percentages are fat, protein, and carbohydrates represented. What is the appropriate ratio of animal to plant-based foods?
With the aforementioned difficulties in mind, I will try to limit my review on Paleo nutrition to randomized trials and meta-analysis of such trials whenever possible, thus limiting observational studies. I will also try to limit my review to studies on humans, as animal research is not easily applicable to our purpose. For example, thousands of studies have used a rodent model for dietary assessment, yet rats and many other rodents do not have a gallbladder, an important organ for fat digestion.
Optimal Dietary Approach
Ultimately, each person is an individual. Although I believe that one’s nutritional intake should mimic the ancestral region from which they came, this can be fine-tuned based on laboratory testing. When following any dietary pattern, testing is warranted for cardiovascular risk, including quantitative serum lipoprotein assessment; markers of inflammation and oxidative stress; blood sugar, insulin, and glycohemoglobin; 25-hydroxy vitamin D; homocysteine; and omega-3 indices. In addition, noninvasive measurements such a salivary nitric oxide, carotid intima-media thickness (CIMT), echocardiography, and heart rate variability and other parameters will help us perfect the nutritional plan. Finally, continued research into areas of fasting and seasonal eating patterns will guide future health practitioners in the dietary optimization of their patients.
In the following review on Paleo and cardiovascular health, I will try to focus on data including Paleo versus other diets, low-carbohydrate versus low-fat, saturated fat intake, animal meat consumption, and seafood consumption as they relate to cardiovascular outcomes and risk factors.
Why Is Paleo the Best Diet for Cardiovascular Health?
The authors of a novel literature review entitled Biological and Clinical Potential of Paleolithic Diet, that spanned 17 years and encompassed 200 scientific journals concluded that the Paleolithic diet is the best diet for preventing Western diseases. This review highlighted the need to look to “evolutionary biology” and “evolutionary medicine” for preventing chronic diseases. Furthermore, the authors concluded that the diets of our ancestors would have been much higher in nutritional value and aided in the prevention of diseases such as atherosclerosis, stroke, heart disease, and insulin resistance. The authors of this article contend that Paleolithic nutrition promotes health, whereas, conversely, they argue that the components of the Standard American Diet (dairy, cereals, refined carbohydrates, and salt) cause disease.8
The author Geoffrey Rose indirectly and eloquently highlighted the importance of studying prehistoric populations for insight into health and disease. His article, entitled Sick Individuals and Sick Populations, called for a shift in how we view the etiology of disease. Rather than look at an individual’s risk for disease, he contends it is more helpful to look at why certain populations remain healthy, whereas others get sick. As an example, he quotes, “We might achieve a complete understanding of why individuals vary, and yet quite miss the most important public health question, namely, ‘Why is hypertension absent in the Kenyans and common in London?’. The answer to that question has to do with the determinants of the population mean; for what distinguishes the two groups has nothing to do with the characteristics of individuals, it is rather a shift of the whole distribution —a mass influence acting on the population as a whole. To find the determinants of prevalence and incidence rates, we need to study characteristics of populations, not characteristics of individuals.” This population prevention strategy is more effective in mitigating chronic disease as it works to alter exposures to be more favorable in the whole population. This allows for more sustainable lifestyle and behavior changes on a large scale in society that need to take place to eradicate our modern diseases. It also allows us to be guided by evolutionary biology.9
Paleo and Mortality
The ultimate arbiter of any health outcome must be mortality. Unfortunately, there are no randomized trials dedicated to mortality on Paleo nutrition versus other diets. The closest trial we have is the 2017 REGARDS (Reasons for
Geographic and Racial Differences in Stroke) study assessing the diets of 21,423 participants. They looked at outcomes of quintiles based on adherence to a Paleo diet. The authors found a 23% lower risk of death in the group most adherent to Paleo nutrition principles versus the quintile with the lowest compliance, although other confounding factors were present. A 28% reduction in cancer deaths and a 22% reduction in cardiovascular death was noted in the high- versus low-adherence group.10
Geographic and Racial Differences in Stroke) study assessing the diets of 21,423 participants. They looked at outcomes of quintiles based on adherence to a Paleo diet. The authors found a 23% lower risk of death in the group most adherent to Paleo nutrition principles versus the quintile with the lowest compliance, although other confounding factors were present. A 28% reduction in cancer deaths and a 22% reduction in cardiovascular death was noted in the high- versus low-adherence group.10
An excellent trial assessing mortality in reference to the type of fat intake was the Minnesota Coronary Experiment. In 2016, the long-term outcomes of people randomized to diets of either high saturated fat or high polyunsaturated fat from corn oil was released. This study was based on data acquired in the late 1960s and included human participants who were institutionalized. Adherence to study protocol was meticulous in this highly controlled population. What the authors found was quite the contradiction to common modern dietary recommendations. Although the polyunsaturated group had dramatically lower total cholesterol, mortality INCREASED (emphasis mine) as serum cholesterol was reduced. There was a 22% higher risk of death for each 30 mg/dL reduction in serum cholesterol.11 The authors of the Minnesota Coronary Experiment study also added a meta-analysis of five other randomized trials and concluded a higher risk of death in groups randomized to polyunsaturated fat versus saturated fat. A large meta-analysis of observational studies assessing over 300,000 people confirmed that consumption of saturated fat does not lead to excess mortality, myocardial infarction, or stroke risk, as reported in the British Medical Journal.12 Substituting saturated fat for polyunsaturated fat does not reduce mortality from cardiovascular disease according to data from the Sydney Diet Heart Study and additional meta-analysis.13
Meat/Seafood/Eggs and Mortality
A 2014 meta-analysis of meat consumption found that unprocessed red meat did not lead to excess mortality, although processed meat did. Again, this analysis was based on data from observational trials.14 A 2010 meta-analysis including over 1,000,000 persons found no link to unprocessed red meat and cardiovascular mortality.15 Processed meats likely increase risk because of several factors including preservatives, cooking methods, meat quality, and lifestyle behaviors of those who consume these foods.
Fish eaters enjoy a 12% lower risk of death compared with non-fish eaters in a meta-analysis of over 650,000 people.16 Another recent meta-analysis of over 400,000 people found a 9% lower risk of death in men who consumed the most fish, 8% in women.17 Of note, women who ate the most fish enjoyed 38% lower risk of mortality from Alzheimer disease. A study often used by those promoting a vegan nutrition plan is the data from the Seventh Day Adventists. Yet the group of Seventh Day Adventists with the lowest mortality were those in the pescatarian group. Fish-eaters enjoyed a 19% mortality reduction compared with the group described as nonvegetarian. Other variables were noted between groups, including differences in exercise, tobacco use, and alcohol consumption.18 Marital status and ethnicity may also play a role in results.
The food that seems to conjure the most critique among the diet gurus is the egg. The egg graced the cover of Time magazine in 1984 as the anticholesterol poster food. A 2017 study on over 40,000 people found that those who consumed the most eggs had a 12% reduction in overall mortality.19 A recent article reviewing the massive amount of literature on eggs ended with the authors concluding, “The evidence suggests that a diet including more eggs than is recommended (at least in some countries) may be used safely as part of a healthy diet in both the general population and for those at high risk of cardiovascular disease, those with established coronary heart disease, and those with type 2 diabetes mellitus.”20
Other Paleo Foods and Mortality
Coconut and coconut oil are often ridiculed and regarded as unhealthy by nutrition authorities including the American Heart Association.21 Despite the health and wellness of island populations consuming coconut, there is a paucity of research regarding mortality. A recent review of palm oil consumption, an oil with a similar nutritional profile to coconut oil, found no increased risk of mortality in palm oil users.22
Nuts and seeds would fall into the category of paleolithic foods, although our ancestors would struggle to crack nuts from shells. Store-bought walnuts shelled into a bag is a lot easier to eat than cracking one by one. Seeds, dried out of a pumpkin or sunflower, were likely an easier proposition. People who consume the largest amount of nuts and seeds enjoy a much lower risk of dying. In one study, nut eaters of over three servings per week led to a 29% lower mortality than those who did not eat nuts/seeds.23 Another study from 2016 displayed similar findings including lower total mortality and cardiovascular mortality in the group consuming the most servings of nuts per week.24
Paleo Lifestyle and Mortality
Paleo nutrition is the subject of this chapter as it pertains to cardiovascular risk and overall mortality, but nutrition is obviously only one part of overall lifestyle considerations. Other factors may be just as important as the food we eat including sleep, sun exposure, tobacco use, and physical activity.
The origins of diseases of affluence, as opposed to diseases of infection, have long been speculated. In 2008, a professor known as Johan Mackenbach published a short article in the Journal of Epidemiology and Community Health. He claimed that the pathogenesis of chronic disease in humans arises from two factors: (1) effects to the internal system of humans arising from interactions within the external environment and (2) effects to the internal system of humans arising from a failing of internal physiological mechanisms. This important contention highlights the fact that every single cell in our bodies is affected by the effects of both our internal and external environments. External environment can be diet, toxins, exposure to the sun, and even physical activity. It is what our bodies are exposed to on a daily basis.25
Another study further corroborates this contention, stating that disease is the direct result of both the health inside the body and the “healthy” or “unhealthy” exposures outside the body.26
This idea warrants questioning of how our environments have changed throughout evolution. Both the diet and lifestyle of our discordant Westernized society today is much different from that of hunter-gatherer societies of long ago. As a result, there are now “diseases of civilization,” such as cardiovascular disease, that are the direct result of changes to the environment we live in. Thus, when looking for diet and lifestyle causes of cardiovascular disease, it is beneficial to examine the effects of the divergence from a traditional hunter-gatherer society to one rooted in agrarian ways.27
The modern world is burdened with increased antinutrients, toxins, pharmaceuticals, physical inactivity, and heightened levels of stress. These factors all take their toll on health over time. To prevent and reverse disease, one must alter these other lifestyle factors along with diet to achieve better health outcomes and reverse chronic disease rates.
Energy expenditure through physical activity was an important part of survival for the ancestral hunter-gatherers of long ago. Activities included foraging and hunting for food and water, creating shelter, interacting with others, and protecting themselves from predators. This highly active lifestyle is much different from the modern sedentary lifestyle we see in society today. In fact, the authors of one study make the case that the shift from the traditional “hunter-gatherer” lifestyle to one in which people are “sedentary, overfed and always indoors” is associated with the rise of disease, obesity, depression, and weakness experienced today. The primal link between energy intake and energy expenditure has been abolished owing to the modern world, and as a result the health of society has been drastically impacted.28
A “real world” field setting study analyzed activity patterns similar to those found during the Paleolithic period. Four healthy men were recruited to undertake a 12-day Alaskan backcountry hunting immersion. The results showed negative energy balance, along with reductions in body fat, total fat mass, visceral fat volume, and intrahepatic lipids. There was also a pattern of reduced low-density lipoprotein (LDL) cholesterol. Interestingly, lean tissue mass was preserved. This emulation of the hunter-gatherer lifestyle showed increased rates of total energy expenditure, improved lipid profiles, and beneficial metabolic effects.29
The Iowa Women’s Health Study looked at nutrition AND other lifestyle factors as to their evolutionary concordance. They recruited and followed a population-based cohort of 41,837 postmenopausal women in Iowa from 1986 to 2012 to identify if diet, body fat distribution, and other risk factors increased the incidence of cancer and all-cause mortality. The findings of this research endeavor revealed that there was a significant inverse association between individuals following an “evolutionary-concordant” diet and lifestyle pattern and all-cause mortality.30 The key here was the LIFESTYLE. What can be described as a Paleo diet versus Mediterranean did not matter. What mattered was the lifestyle.
Weston A. Price was a dentist who traveled the world studying groups of people who followed an ancestral nutrition and lifestyle pattern. He found health and wellness without the chronic disease states found in the developed world. For example, traditional hunter-gatherer-type diets like those of the aboriginal Arctic Eskimos were historically low in carbohydrate and high in protein. The traditional diet consisted of wild land and sea animals and fish and was found to be a complete source of essential nutrients despite limited selection. An article written in 1977 in the American Anthropologist concluded that the “modern” Eskimo, who has been exposed to dietary acculturation and has veered away from traditional diet and lifestyle, is known to experience the same chronic diseases that affect the US population, including obesity, cardiovascular disease, hypertension, and tooth decay.31 Furthermore, a study published in the American Journal of Clinical Nutrition concluded that, “it is likely that no hunter-gatherer society, regardless of the proportion of macronutrients consumed, suffered from diseases of civilization.” These diseases of civilization include obesity, cardiovascular disease, and type 2 diabetes (T2D), to name a few.32
A unique historical perspective review concluded that, although life expectancy has increased, there are still low levels of “healthy life expectancy,” defined as less suffering from chronic disease before death. A review compared diet and lifestyle behaviors of primitive populations of the past with that of the modernized societies of today. The finding is that modern diets are drastically different from those of the past with less variability, a declining nutritional value, and an increased intake of calories, all of which impact total mortality and chronic disease risk. Furthermore, the review artfully concluded that the true difference in health outcomes is a result of differences in food intake. Hunter-gatherer populations focused on “eating to live,” whereas Westernized societies of today have shifted to a focus of “living to eat” and this is where health problems have arisen.33
Paleo and Lipids
Foods common on the Paleolithic diet are considered by many to negatively impact the lipid profile. Meat, eggs, coconut, and other sources of saturated fat and/or dietary cholesterol have been vilified by many health authorities and promoted as foods to avoid. The reality is that these foods are beneficial for cardiovascular protection.
Much of the attack on red meat consumption centers on its association with abnormal cholesterol levels. But publicity and perception around this link may not be the reality. A recent meta-analysis of 24 randomized trials concluded that total red meat intake of ≥0.5 servings/d does not negatively influence cardiovascular disease risk factors, compared with those who consume red meat <0.5 servings/d. There were no significant differences in total cholesterol, LDL, high-density lipoprotein (HDL), or triglycerides.34
A 2004 trial comparing very low-carb to low-fat in human participants concluded, “The short-term hypoenergetic low-fat diet was more effective at lowering serum LDL-C, but
the very low-carbohydrate diet was more effective at improving characteristics of the metabolic syndrome as shown by a decrease in fasting serum TAG, the TAG/HDL-C ratio, postprandial lipemia, serum glucose, an increase in LDL particle size, and also greater weight loss (P < .05).”35
the very low-carbohydrate diet was more effective at improving characteristics of the metabolic syndrome as shown by a decrease in fasting serum TAG, the TAG/HDL-C ratio, postprandial lipemia, serum glucose, an increase in LDL particle size, and also greater weight loss (P < .05).”35
In a 2-year Dietary Intervention Randomized Controlled Trial – Carotid (DIRECT-Carotid) study, participants were randomly assigned to a low-carbohydrate, low-fat, or Mediterranean treatment group. Authors looked at the effect of diet on serum lipoproteins. The Apo B to Apo A ratio may be the best conventional lipid marker used to assess cardiovascular risk.36 The results showed a significant reduction in the ratio of apolipoprotein B(100) to apolipoprotein A1 in the low-carbohydrate group compared with the low-fat group. Over time, the low-carbohydrate group experienced the greatest significant increase of Apo A1 compared with the low-fat group. Furthermore, levels of Apo B100 were significantly increased in the low-fat group.37
Seafood has been recognized for millennia for its sustenance value. A review from the College of William and Mary in 1944 found that seafood, particularly shellfish, are a complete food. Seafood contains fat, protein, and limited carbohydrates including a full complement of minerals (best source of iodine) and vitamins, including A, B, D, E, and K. Only shellfish have appreciable levels of vitamin C.38 A 2018 trial found that fatty fish consumption increases HDL particle number and size, both recognized as cardioprotective changes.39 This is confirmed in multiple studies.40
Coconut and coconut oil have been vilified for years because of their high content of saturated fat. Despite this fact, islands in the South Pacific have very high consumption of coconut and enjoy excellent health.41 A recent prospective randomized analysis compared coconut oil with butter and olive oil. Study participants were asked to consume 50 g of their assigned fat. Coconut oil was found to be neutral on LDL, increase HDL, and improve the total cholesterol (TC)/HDL ratio.42 Another 2017 randomized trial among young men in Thailand found coconut oil at 30 mL/d had a nonsignificant effect on TC and LDL but led to a 5.72 mg/dL increase in HDL concentration.43 Finally, a 2017 study on postmenopausal women found that coconut oil raised TC, LDL, and HDL, thus preserving the TC/HDL ratio. The study authors conclude coconut oil to be safe but also recommended that future studies use advanced lipoprotein analysis including particle numbers.44
Recent evidence has shown that saturated fat is cardioprotective and can change LDL particles from a small, dense size to large size.45 Saturated fat can modify the particle size to a benign type that can actually reduce cardiovascular risk. A low-carbohydrate diet can promote positive changes on particle size, whereas the opposite is true for a low-fat diet.46 A study of genetically predisposed children found that a high-carbohydrate, low-fat diet can induce a particle size change in LDL from large to small and dense.47 In a study of men with a majority of large LDL particles, a low-fat diet had adverse effects. The low-fat diet shifted LDL particle size to small, reduced HDL concentrations, and increased triglyceride levels.48
Thirty-two participants were randomized to a Paleo diet versus the Dutch diet for 2 weeks. The Dutch diet has a similar macronutrient breakdown to the Mediterranean diet. In this short period of time, the Paleo group saw a significant reduction in total cholesterol and triglycerides and an increase in HDL versus the reference Dutch diet.49
Paleo bested the Diabetes diet in individuals with T2D. The study concluded that being on a Paleo diet short-term is beneficial for lipid profiles compared with an American Diabetes Association (ADA)-recommended diet (one rich in grains, added salt, and low-fat dairy).50 A Paleo diet resulted in significant reductions of cardiovascular risk factors, including decreased triglycerides and increased HDL, as compared with a Diabetes diet.51
Paleo and Blood Pressure
A novel postulation published in 2018 in Medical Hypotheses stated that the hypertension of modern American society is the result of a diet that is low in potassium, depleted of antihypertensive phytochemicals, and high in sodium. The authors contend that the effects of this type of diet results in essential hypertension caused by oxidative stress and restricted nitric oxide bioavailability. They reveal that the current intake of potassium-to-sodium (in molar ratio) of Americans is less than or equal to 1. Conversely, our Paleolithic ancestors consumed molar ratios of potassium-to-sodium at levels of 5 to 10 or greater. Indeed, this highlights a dire need for increased potassium in the diet.53 It is widely known that patients with a low dietary intake of potassium have an increased risk for hypertension and cardiovascular-related issues. Furthermore, the less-than-ideal ratios of potassium to sodium experienced in the Standard American diet (including a deficiency of potassium and surplus of sodium) contributes to intracellular acidity, a known risk factor for vascular endothelial dysfunction.53
Most health authorities agree that sodium consumption is causative of hypertension. The highest risk of hypertension is in those who consume high sodium, especially in relation to potassium intake. A study was done on chimpanzees and found that the addition of salt to the monkey diet led to progressive high blood pressure.54
In humans, a Paleo diet was compared with a Diabetic diet in those with T2D. The Paleo group enjoyed a significant blood pressure drop in this short-term trial. The Diabetes group did not.51 Observational data on over 3000 people in Korea found that a low consumption of eggs and meat was linked to a higher risk of hypertension. Salted seafood consumption was also a risk factor for hypertension in this study.55 Fish consumption is linked to lower blood pressure in several studies.56 High cellular levels of omega-3 docosahexaenoic acid (DHA) demonstrated a 36% lower risk of hypertension.57
Impaired endothelial function is a risk factor for hypertension. A low-carbohydrate diet has been shown to improve carotid endothelial function. In the DIRECT-Carotid study, participants were randomly assigned to low-carbohydrate, low-fat, or Mediterranean diet treatment group and analyzed
for changes to carotid artery thickness and carotid vessel volume. The results showed a regression of carotid vessel volume and a decrease in carotid artery thickness in all three treatment groups at 2 years.37
for changes to carotid artery thickness and carotid vessel volume. The results showed a regression of carotid vessel volume and a decrease in carotid artery thickness in all three treatment groups at 2 years.37
A recent 2019 randomized trial looked at subjects receiving varying levels of glycemic load and glycemic index foods on arterial stiffness. A diet with low-carbohydrate and low glycemic index was found to support healthy vascular tone.58
A study analyzed the effects of a very-low-carbohydrate diet on risk factors of cardiovascular disease including endothelial function. The study found that markers of endothelial function, including E- and P-selectin, ICAM1, plasminogen-activator inhibitor 1, and tissue-type plasminogen activator were significantly improved by a carbohydrate-restriction diet.59
Paleo and Blood Sugar/Metabolic Syndrome
Elevated blood sugar, diabetes, and the metabolic syndrome are all considered risk factors for cardiovascular disease. It would behoove us to find the best diet for glycemic control. The Standard American Diet tends to be rich in highly processed, empty calorie foods and as a result depleted of many essential nutrients required for health. It is often linked with the pathogenesis of postprandial dysmetabolism, including hypertriglyceridemia, elevated glucose, and elevated insulin. Postprandial dysmetabolism is associated with oxidative stress, inflammation, and subsequent atherogenic changes. Authors of a 2008 JACC study concluded that an anti-inflammatory and minimally processed diet along with a healthy lifestyle can play a role in the prevention of postprandial dysmetabolism.60
A 2018 randomized trial found that those participants placed on a high-fat diet versus high-carbohydrate enjoyed lower blood sugar during the fasted and postprandial state.61 The Paleo diet exhibits fewer calories and lower glycemic index spikes and is more satiating, and as a result it causes greater decreases in weight and waist circumference and is favorable for reversing metabolic disease.62
Further studies corroborate beneficial effects on cardiovascular risk factors in T2D. Two groups were randomized to either a Paleolithic diet or the standard ADA diet. HbA1c and other parameters of the metabolic syndrome were markedly improved on Paleo versus ADA.51
Paleo was compared with Mediterranean in patients with coronary artery disease (CAD). Twenty-nine patients with CAD plus either glucose intolerance or T2D were randomized to receive (1) a Paleolithic diet (n = 14), based on lean meat, fish, fruits, vegetables, root vegetables, eggs and nuts; or (2) a Consensus (Mediterranean-like) diet (n = 15), based on whole grains, low-fat dairy products, vegetables, fruits, fish, oils, and margarines. Primary outcome variables were changes in weight, waist circumference, and plasma glucose AUC (area under curve) and plasma insulin AUC in OGTTs. The results were clearly in favor of Paleo. Over 12 weeks, there was a 26% decrease in AUC glucose in the Paleolithic group and a 7% decrease in the Consensus group. Weight circumference reduction was 2× greater in the Paleo group.176
A review study compared 28 reports of data on the diets, lifestyles, and metabolic effects of traditional hunter-gatherer Australian Aborigines versus Westernized Aborigines. The results were striking. When Aboriginals lost their traditional hunter-gatherer lifestyle, they developed an increased rate of abdominal adiposity, obesity, impaired glucose tolerance, hyperinsulinemia, non-insulin-dependent diabetes, and hypertriglyceridemia, all of which are early and established risk factors for cardiovascular disease. Before Australia became colonized, Aborigines lived as traditional hunter-gatherers. The review concluded that there is no evidence that these traditional hunter-gatherer Aboriginals experienced any of the chronic diseases, or diseases of civilization, we see in the Western society today.63 It has been shown that when Westernized Aborigines reverted to a traditional hunter-gatherer lifestyle for a short term (2 week) or long term (3 month) period, there are significant reductions of circulating insulin and triglyceride levels.64,65
In one study, agricultural versus hunter-gatherer societies were compared. Fifty-nine healthy Shuar Amerindian women living in five isolated communities in the Ecuadorian Amazonian rainforest were included in the study. Women who were from regions that were more dependent on agriculture had stark metabolic differences compared with traditional hunter-gatherer populations. These discrepancies show an increased risk of metabolic syndrome due to agricultural living as a result of increased fat mass, higher leptin, increased plasma insulin, and increased plasma triglycerides.66
Another study of Paleo versus Mediterranean found that Paleo was more satiating and led to lower calorie intake. Leptin, a hormone released from adipose tissue was lower in the Paleo group.67 Leptin is implicated in the control of food intake via appetite suppression and may also stimulate oxidative stress, inflammation, thrombosis, arterial stiffness, angiogenesis, and atherogenesis.68
In a metabolically controlled study of obese patients with T2D, 14 participants were assigned to a Paleo diet and 10 were assigned to a conventional diet based on recommendations made by the ADA. The results revealed that those on a Paleo diet had greater improvements to glucose control and lipid profiles. Another astounding finding was that participants with the most insulin resistance had a significant increase of insulin sensitivity on the Paleo diet. Conversely, insulin-resistant participants on the conventional ADA diet did not experience significant improvements in insulin sensitivity.50
In a review of randomized control trials conducted thus far, the study found that the Paleo diet resulted in better improvements for the five components of metabolic syndrome (waist circumference, triglycerides, HDL, blood pressure, and fasting blood sugar) than the four control diets, which were all similar diets based on national nutritional guidelines.69
It has been concluded that the Western diet consisting of grains, sugar, and dairy promotes insulin resistance and disease pathogenesis through its pleiotropic effects on insulin/IGF-1 signaling (IIS). Up-regulation of IIS is associated with hyperglycemia, hyperinsulinemia, oxidative stress, and B-cell dysfunction, all of which lay the framework for T2D and cardiovascular disease. Although access to these hyperglycemic and insulinotropic foods became available roughly
10,000 years ago, it is proposed that our human genomes have not yet adapted to this type of diet and its increased activation of ISS. Dietary behaviors (elimination of sugar, grains, and dairy) such as those found on the Paleo diet can lower ISS and are speculated to reduce disease pathology as a result.70
10,000 years ago, it is proposed that our human genomes have not yet adapted to this type of diet and its increased activation of ISS. Dietary behaviors (elimination of sugar, grains, and dairy) such as those found on the Paleo diet can lower ISS and are speculated to reduce disease pathology as a result.70
T2D is associated with an increased risk for neurodegenerative disease including a decline in cognition. A clinical trial published in 2017 randomized T2D patients taking metformin to a Paleolithic diet with and without high-intensity exercise for 12 weeks. The study found that both interventions resulted in significant weight loss, improved insulin sensitivity, decreased HbA1C, reduced triglycerides, and increased oxygen uptake. Additionally, with both intervention groups there was increased BDNF, increased functional brain responses, and increased gray matter volume in the right hippocampus, all of which are neuroprotective and can stimulate synaptic plasticity.71
A clinical trial had 32 individuals with T2D follow the Paleo diet ad libitum for 12 weeks. They were then randomized to standard care exercise or supervised exercise training. Both groups had significant weight loss and reductions in fat mass. Additionally, the Paleo diet treatment resulted in significant decreases in liver fat and intramyocellular lipid content.72 Fifty-eight overweight women were assigned to a Paleo or control diet for 24 months. Results showed that the Paleo diet surpassed the control diet with improved insulin sensitivity.52
Paleo Diet and Weight Management
Obesity is a significant risk factor for cardiovascular disease and overall mortality. In the general population, obesity increases overall mortality by 250% compared with an ideal body weight.73 Research has shown that for traditional hunter-gatherer and subsistence farmer populations engaged in increased amounts of physical activity and with limited exposure to highly processed, high-calorie foods, there is little to no evidence of obesity or metabolic disorders.74 The Physicians Health Study found that men had a 42% lower risk of cardiovascular events and women a 35% lower risk in the group with normal waist to hip ratio compared with the highest category.75
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