Beginning in the early 1960’s the American Heart Association began to publicly recommended that saturated fats in the diet (e.g., fats from dairy, meats, and tropical oils) be replaced with sources of polyunsaturated lipids from vegetable oils. As the makers of agricultural vegetable oils reinforced this message with incessant advertising, the production and preparation of all types of food began to change significantly. Fast–food (and most other) restaurants eventually switched to the nearly exclusive use of vegetable oils for cooking and frying. At home, the use of salad oils, margarine, and related vegetable–based shortenings increased greatly, as these items were often deemed to be healthier replacements for previously–used butter, lard, and tropical oils. The production of packaged foods such as crackers, potato chips, tortilla chips, bread, cookies, and other baked goods traditionally relied on the stability of animal or tropical oils to keep these products fresh – but in the light of saturated fat’s new stigma, these products, too, began to be made almost exclusively with polyunsaturated vegetable oils.
All told, recent decades have seen a dramatic increase in the worldwide consumption of polyunsaturated fats and oils. This intervention, however, has not only failed to reliably reduce blood lipids (i.e., cholesterol and triglycerides) as predicted, but has also failed to reduce the risk of cardiovascular disease or overall mortality. Some studies have shown, in fact, that the addition of polyunsaturated fatty acids (PUFAs) to the diet at the expense of saturated fat may actually lead to increases in cardiovascular and overall mortality – including disconcerting increases in the incidence of cancer.
Despite clear reason to question the safety of the polyunsaturated fats they contain, the low cost and profitability of vegetable oils and vegetable–based margarine has helped them remain popular with food producers for decades. Although never eaten by our distant ancestors, industrial oils such as soybean oil, corn oil, cottonseed oil, safflower oil, sunflower oil, and canola oil now represent the vast majority of edible oils consumed in the world today.
The dramatic increase in the polyunsaturated fatty acid content of the American diet has also coincided with a shocking increase in the rates of diabetes and obesity. Between 1971 and 2000, the intake of saturated fat in the U.S. diet remained reasonably constant. As daily caloric intake increased during this time, the percentage of overall calories derived from saturated fat actually declined. The amount of PUFA in the average American diet, on the other hand, increased significantly, and continues to climb – both in absolute amounts and as a percentage of overall calories consumed. In the early part of the Twentieth Century, the average American diet may have contained 15 grams of PUFA daily – constituting roughly 5% of daily calories. In recent years, however, the average intake of PUFA in the American diet has climbed to almost 40 grams per day – equaling over 13% of daily calories.
Paralleling increased PUFA consumption, between 1971 and 2000, the prevalence of obesity in the United States increased from 14.5% to 30.9% of the population. The current rate of obesity is nearly 34%, and some experts have predicted that this number will gradually increase to 42% over the coming decades.
The incidence of diabetes has similarly paralleled both increasing PUFA intake and the increasing rate of obesity. In 1970, diabetes affected under 3% of the population. By 2000, this number had risen to over 6%. Currently, 11% of adults are affected, with some estimates projecting 15% diabetes incidence by 2015 – and up to 33% incidence by 2050. The vast majority of this increase is attributable to type–II diabetes – the type known to largely be influenced by dietary patterns.
America’s declining health and expanding waistlines can’t be attributed entirely to a lack of effort. The billions of dollars Americans spend each year on diet and fitness products are largely being wasted, and the misguided advice of health experts may be partly to blame. In addition to the vegetable oils which are used in the production of “junk foods,” even foods which are widely regarded as healthy, including nuts, nut butters, legumes, seed oils, fish oils, and even olive oil may also be contributing to an excess of certain unsaturated oils in the modern diet. Where such foods are often over–emphasized by health–conscious consumers, they may be responsible for unique PUFA imbalances in those who attempt to eat a healthy diet – especially if these foods replace traditional sources of saturated fat and related fat–soluble nutrients.
Overall, the food–consumption data of the past several decades gives reason to hypothesize that an excess of PUFAs may be a major (if not the major) contributing factor to the modern epidemics of obesity and diabetes in the industrialized world. The biological effects of polyunsaturated fats seem to lend support for this hypothesis as well. We find that an excess of these fats may lead to chronic inflammation, immune dysfunction, increased lipogenesis (i.e., the creation of fat cells), impaired thyroid functioning and thyroid hormone signaling, reduced metabolic rate, liver damage, and impaired glucose metabolism.
When these “essential fatty acids” are largely excluded from the diet, however, we find that metabolism increases, weight is lost, immune function improves, liver function is enhanced, blood sugar is normalized, and both animals and humans become remarkably resistant to the harmful effects of toxic (including cancer–causing) substances. If modern diet–related epidemics like those of diabetes and obesity are to be reversed, what’s desperately needed is meaningful perspective on the types, amounts, and ratios of fats which truly have a place in the healthy human diet.
Fats in Traditional Diets
Most people in industrialized nations today have spent their entire lives surrounded exclusively by foods of industry and commerce. As such, it’s understandable that many people (even health–conscious people) may lack an understanding of traditional methods of food preparation, or the nutrient composition of traditional, pre–industrial diets.
Diet–related disorders, including and especially obesity and diabetes, are nearly non–existent in cultures still consuming traditional foods. As such, it’s likely that these diets can give us important clues as to the causes and solutions to our modern diet–related epidemics of disease.
Healthy pre–industrial diets vary widely in their nutrient composition because of the different foods available in different geographical regions – but one common thread uniting these different diets is their relatively low levels of plant–based omega–6 fats, most notably, the polyunsaturated omega–6 fat known as linoleic acid.
Though only found in small amounts in most whole foods, linoleic acid is abundant in modern oils often used in cooking and industrial food preparation. Safflower, sunflower, corn, soybean, canola, and cottonseed oils are some of the more common sources of linoleic acid in the modern diet. Even generally healthier sources of fatty acid like nuts, seeds, avocados, and olive oil, however, may still contribute to an excess of linoleic acid in the overall diet. Also, some animal fats, like pork (lard) and chicken fat will contain surprisingly high levels of linoleic acid as these animals are often fed oils from corn and soybeans.
The extraction of oils from corn, soybeans, rapeseeds (i.e., canola), cottonseeds, sunflower/safflower seeds, et al – and the presence of these oils as a significant source of dietary calories – are uniquely modern phenomena without precedent in traditional diets.
Products of commercial agriculture like vegetable oils give societies the ability to produce consistent and reliable sources of food at a modest cost. By reducing the risk of famine, agriculture and industry are largely responsible for supporting massive population growth. As part of a self–sustaining system, larger populations necessitate increased reliance on agriculture to produce the massive amounts of food needed to sustain such populous societies.
Oftentimes, however, the food products of industry leave much to be desired nutritionally. Though these foods may sustain life, it’s simply impossible for the human body to function optimally on a diet for which it was not designed. The sort of high–PUFA oils so common to us today are perhaps the quintessential example. A look at traditional diets reveals that, although they consumed different foods, traditional cultures around the globe universally consumed remarkably low levels of the plant–based omega–6 oils so common in our modern industrial diets.
Throughout history, for example, many hunter–gatherer societies thrived while relying heavily on muscle and organ meats from land animals. Unlike vegetable oils, animal fats will contain low levels of polyunsaturated fatty acids, and higher levels of monounsaturated and saturated fatty acids. Furthermore, if an animal happens to be a ruminant (e.g., cow, goat, sheep, bison), bacteria in the animal’s rumen can stabilize and “detoxify” the polyunsaturated lipids from their diet. This may make lipids from ruminant animals uniquely health–promoting for humans. The Masai tribe of Kenya, for example, thrives while consuming little more than milk, meat, and blood from their cattle:
Study Link – The Teeth of the Masai.
Quote from the above study:
The principal food of the Massai is milk, meat and blood, the latter obtained by bleeding their cattle. The protein consumption, therefore, is extremely high, while that of carbohydrate is negligible.
Surprisingly to many, the Masai tribe is known to exhibit particularly low incidence of Western diet–related disorders including obesity, diabetes, and heart disease. This is despite (or perhaps, because of) a notably high intake of saturated fat. As the above study details, their incidence of another disease of industrialization, periodontal disease, is remarkably low as well.
But not all healthy traditional cultures eat low–carbohydrate and land animal–based fare like the Masai, however. Some cultures, including inhabitants of the island of Kitava, Papua New Guinea thrive on starchy tubers (e.g., sweet potatoes), fruit, fish, and coconut. Researchers have noted that Kitavans exhibit extreme leanness despite living amidst an abundance of food. Interestingly, researchers have also noted that genetic factors are unlikely to play a role in the Kitavan’s low incidence of diabetes and cardiovascular disease. It seems they’re quite prone to developing these disorders when adopting a Western diet, however:
Quote from the above study:
The population is characterized by extreme leanness (despite food abundance), low blood pressure, low plasma plasminogen activator inhibitor 1 activity, and rarity of cardiovascular disease. Tubers, fruit, fish, and coconut are dietary staples whereas dairy products, refined fat and sugar, cereals, and alcohol are absent and salt intake is low…[G]enetic factors do not appear to explain the rarity of cardiovascular disease and diabetes in traditional populations. On the contrary, after adopting a Western lifestyle, subsistence horticulturalists and traditional Pacific Islanders in particular…are more prone to developing diabetes and cardiovascular disease than are populations of northern European ancestry.
Similarly to Kitavans, Polynesian islanders have been studied, and have been found to exhibit robust health on a diet including coconut, fish, fruit, and starchy root vegetables. Again, despite the common mistaken assumption that saturated fats cause heart disease, Polynesian diets containing up to 47% of calories as saturated fat (the majority of which coming from coconut) are not associated with coronary heart disease:
Quote from the above study:
Coconuts are used extensively in the diet in many different parts of the world. These populations are in the developing world where coronary heart disease is uncommon or rare. Certainly, there is no reason based on this report, to alter the diet patterns of coconut eating groups in order to reduce coronary risk.
Notably, the diet of the islanders in the above study is fairly typical of traditional diets in that it contains nutrient–rich foods and low levels of polyunsaturated fats (PUFAs comprise 2–3% of overall calories). In addition, a small amount (but a significant fraction) of the polyunsaturated fats in these diets is certain to come from the omega–3 series lipids found in fish. By implication, the level of omega–6 fatty acids in these diets is certain to be remarkably low (~1%).
Even the relatively PUFA–rich diet of traditional Greenland Inuits, consisting largely of fish and seal blubber, is likely to contain only ~ 5% of calories as the omega–6 fat, linoleic acid. As fish oil supplement marketing has emphasized in recent years, the Inuit diet is notable for its high content of omega–3 fatty acids:
Study Link – The composition of the Eskimo food in north western G reenland.
Quote from the above study:
One of the most marked differences was that the polyunsaturated fatty acids belonging to the n–6 family were in Eskimos replaced by those belonging to the n–3 family.
Note: although traditional Inuit diets are not associated with heart disease or diabetes, evidence suggests that their diet may have been less than optimal. Inuit populations are at notable risk of bleeding disorders, stroke, infection, and, as noted arctic explorer, Vilhjalmur Stefansson, noted, they appear to age prematurely. Many non–diet related factors may be involved, but it’s also possible that the uniquely high levels of peroxidized lipids from omega–3 fatty acids may play a role as well. Out of all traditional diets to emulate, the Inuit diet seems among the least desirable due to their low intake of fruits and vegetables and particularly high intake of omega–3 fats.
By contrast to traditional cultures, the average diet in the U.S. today contains a relatively large amount of plant–based polyunsaturated omega–6 fatty acids, including linoleic acid. Studies have estimated that the overall PUFA intake of the U.S. diet may be as high as 13%, with close to 9% coming from linoleic acid alone. The average omega–3 content of the U.S. diet is approximately 1.6 grams per day, or approximately 0.7% of overall calories.
See:
Study Link – Polyunsaturated fatty acids in the food chain in the United States.
Recently, in the scientific and popular literature alike, increased attention has been given to the importance of a proper omega–6–to–omega–3 ratio in the diet. While this ratio in the American diet may far exceed 10:1 (some sources estimate that this ratio may even be as high as 20:1), the ratio in healthy traditional cultures is usually 2:1 or lower. The omega–6–to–omega–3 ratio is likely to be an important factor in constructing a healthy diet, but perhaps the most important factor to keep in mind is that the overall PUFA intake should likely be kept low (2–3% of overall calories) as found in many of the healthiest traditional cultures. Despite a common practice today, attempting to “balance” an excessive omega–6 intake by consuming more omega–3 lipids (e.g., flax or fish oil supplements) is likely to do more harm than good because of the chemical instability of all polyunsaturated oils.
As evidence, when the overall intake of PUFA is low, excess omega–6 seems to cause less metabolic disruption than when the overall PUFA intake is high. In newborn rats fed less than 1% of calories as PUFA, the omega–6–to–omega–3 ratio can vary between 0.04 and 12.1 without affecting the DHA (a long–chain omega–3 lipid) content of the brain:
Along these lines, it’s interesting to note that, at 0.7% of calories, the omega–3 content of the average American diet is roughly similar to that of many healthy traditional cultures. Of course, a case could be made that the pre–formed long–chain omega–3s, EPA and DHA, from fish and other animal–based foods are biologically different than the linolenic acid (the most common source of omega–3s in the U.S. diet) found in plant foods (e.g., vegetable oils like canola oil), but for as often as we hear the advice to consume more omega–3s, it’s important to realize that the scientific evidence simply doesn’t support the stance that omega–3s are necessarily deficient in our modern diet.
What the evidence does support, however, is the fact that our excess consumption of omega–6 lipids such as linoleic acid will interfere with the proper metabolism of the omega–3 fatty acids. Studies have clearly shown that the incorporation of omega–3 DHA into tissues is greatly inhibited when animals are fed linoleic acid levels similar to those found in the modern American diet:
Quote from the above study:
…positive effect on DHA status by lowering the LA–ALA [linoleic acid:alpha–linolenic acid] ratio from 10:1 to 3:1 or 4:1, and they predict that ratios of LA–ALA below 4:1 would have little further beneficial effect on DHA status.
To begin to understand why high intakes of omega–6 linoleic acid may be destined to cause the sort of metabolic disruption associated with obesity, diabetes, and other diet–related disorders it will help to investigate the biological effects of this and related polyunsaturated fatty acids.
Linoleic Acid
Linoleic acid is a polyunsaturated fatty acid belonging to the omega–6 series of lipids. It serves as the precursor to arachidonic acid – a key component of phospholipids which comprise cellular structure. Arachidonic acid is, itself, a precursor to numerous chemicals, called eicosanoids, which are involved in the inflammatory response and in cellular signaling. Historically, arachidonic acid was deemed nutritionally essential until it became apparent that the human body can synthesize arachidonic acid from linoleic acid. While arachidonic acid is commonly found in animal–based foods such as meat, eggs, and dairy, its precursor, linoleic acid, is often found in plant foods and vegetable oils such as corn oil, soybean oil, canola oil, and safflower oil.
In a general sense, fatty acids of the omega–6 series are often pro–inflammatory. Non–steroidal anti–inflammatory drugs (NSAIDs), for example – such as aspirin, ibuprofen, and naproxen – act by inhibiting the conversion of arachidonic acid into the inflammatory prostaglandins and thromboxane.
In addition to the omega–6 series, polyunsaturated fatty acids also include lipids in the omega–3 series. Together, omega–6 linoleic acid and omega–3 linolenic acid are known as the essential fatty acids of human nutrition – meaning that they are necessary for life, but cannot be synthesized by the human body. Thanks in large part to the incessant promotion of fish oil supplements in recent years, many people recognize that fatty acids of the omega–3 series may counter the inflammatory effects of omega–6 fats. Although not entirely accurate, for simplicity’s sake, it’s fair to say that the chemicals produced from the omega–6 fatty acids are inflammatory, while omega–3 fatty acids are largely anti–inflammatory.
Both omega–6 and omega–3 fatty acids, however, compete for the same enzymes which drive the production of signaling chemicals in each class. Though, technically, these enzymes preferentially metabolize omega–3 lipids into long chain omega–3 fatty acids like EPA and DHA, the massive excess of linoleic acid in the modern American diet likely overwhelms these enzyme systems, thus inhibiting the production of these important anti–inflammatory substances from omega–3s.
The omega–3 long–chain fatty acids EPA and DHA can be obtained directly from seafood (thus bypassing the need for the desaturase enzyme systems to create them from the parent omega–3, linolenic acid), but, as we’ve seen, high intakes of linoleic acid can even impair the incorporation of pre–formed DHA into tissues. This is why, as relates to lipids, the real problem with the American diet isn’t a lack of omega–3s per se, but a gross excess of omega–6s, largely in the form of linoleic acid.
Though arachidonic acid is an inflammatory precursor, sources of pre–formed arachidonic acid (e.g. animal–based foods – meat, fish, dairy, butter, etc.) don’t seem to have the same negative health effects as linoleic acid. Studies have found that, unlike linoleic acid, high intakes of arachidonic acid don’t seem to impair the incorporation of omega–3s into plasma lipids. This is evidenced by studies of Australian aborigines consuming tropical fish – rich sources of arachidonic acid and the omega–3 fats EPA and DHA, but poor sources of linoleic acid.
Quote from the above study:
The proportions of arachidonic and all omega 3 PUFA [in plasma lipids] rose significantly on the diet.
This is further evidence that the detrimental effects of linoleic acid may stem from this fatty acid’s propensity to inhibit desaturase enzymes, thus inhibiting the metabolism and utilization of the omega–3 lipids. Knowing this, it’s likely that minimizing linoleic and linolenic acid consumption (e.g., vegetable, seed, and nut oils) and instead choosing animal–based sources of pre–formed arachidonic acid and pre–formed long chain omega–3s (e.g., DHA and EPA) will constitute the optimal approach to ingesting the essential fatty acids. Studies have found, for example, that vegetarians (who are likely to consume more plant–based parent linoleic and linolenic acid) have lower levels of EPA and DHA in plasma lipids versus meat eaters:
Quote from the above study:
The proportions of plasma EPA and DHA were lower in the vegetarians and in the vegans than in the meat–eaters.
Similarly, studies have found that consumption of the parent omega–3 linolenic acid is relatively ineffective at increasing DHA levels:
Quote from the above study:
Studies in normal healthy adults consuming western diets, which are rich in linoleic acid (LA), show that supplemental ALA [alpha–linolenic acid] raises EPA and DPA status in the blood and in breast milk. However, ALA or EPA dietary supplements have little effect on blood or breast milk DHA levels, whereas consumption of preformed DHA is effective in raising blood DHA levels.
If the level of linoleic acid in the diet is kept low (i.e., under 2% of calories), the requirement for EPA and DHA will be low as well. As advocated by public health authorities, the consumption of two servings of seafood per week will more than suffice. But, though sea–foods are well–known sources of omega–3s, they are not the only ones. Many people are surprised to learn, that animal fats like those from beef or lamb are also sufficient to supply adequate long–chain omega–3s if linoleic acid intake is kept low.
See:
It’s important that omega–3s not be consumed indiscriminately as this could easily lead to historically–unprecedented intakes with unknown health consequences. As we shall see in subsequent articles in this series, the therapeutic window for omega–3 lipids is likely to be much smaller than many people suspect. Because of the chemical fragility of these fatty acids, an excess of omega–3s can cause major metabolic disruption.
The dietary landscape of the modern industrialized world has caused our fatty acid intake to diverge greatly from the one for which the human body was designed. Ultimately, the stark differences in fatty acid composition of the modern industrial diet relative to traditional diets is having profound implications for the health of those who blindly accept the current nutritional status quo. In addition, the topic of dietary fat in mainstream and popular culture has been so fully obfuscated over the past century, that even health–conscious individuals are often hopelessly confused as to the types and amounts of fat which have a place in a healthy diet. In the upcoming editions of the Integrated Supplements Newsletter, we’ll continue to shed light on the topic, and examine how the fatty acid content of our modern diet is likely to be a major causative factor in modern diet–related disorders including heart disease, cancer, diabetes, and obesity.
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Posted by: after hours GP | April 10, 2012 at 07:30 PM