by Joseph Brasco, MD
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Unfortunately, the debate over the validity of this concept has primarily been waged in the media and lay publications and not in the scientific journals. Many of the popular books which support this position are gimmicky, and often, lack adequate scientific referencing. Yet, at their core is very important concept -- limiting the intake of carbohydrates, (especially as cereal grains and starches), will improve human health.
Some critics claim that reduced carbohydrate diets are a fashion trend. Well, this so called trend actually dates back some time. Anthropological study of early hominids has concluded that they lived as hunters-gathers. While nuts, seeds, vegetation and fruit made up an important part of the hunter- gather's diet, his mainstay was hunted or scavenged animal prey.
More recent evaluations of early man's nutritional patterns by Dr. Loren Cordain, estimate that as much as 65 percent of his calories were derived from animal products. Granted, early man was not eating corn fed Angus beef from Jewel, but he was eating the meat, the organs and the bones of his prey. Essentially, a high protein/fat diet. It was a mere 10,000 years ago (or less) that man began exploiting an agricultural niche.
This transition was made due to decreasing population of large game prey and an increasing population of humans. While undeniable good has transcended this dietary shift, i.e., growth of the human population, establishment of permanent settlements, the inception of civilization itself - man's health may have suffered in the transition.
Generally, in most parts of the world, whenever cereal-based diets were first adopted as a staple food replacing the primarily animal-based diets of hunter-gatherers, there was a characteristic reduction in stature, a reduction in life span, an increase in infant mortality, an increased incidence of infectious disease, an increase in diseases of nutritional deficiencies (i.e., iron deficiency, pellagra), and an increase in the number of dental caries and enamel defects.
In a review of 51 references examining human populations from around the earth and from differing chronologies, as they transitioned from hunter-gathers to farmers, one investigator concluded that there was an overall decline in both the quality and quantity of life.
There is now substantial empirical and clinical evidence to indicate that many of these deleterious changes are directly related to the predominately cereal-based diets of these early farmers. Since 99.99% of our genes were formed before the development of agriculture, from a biological perspective, we are still hunter-gathers.
Thus, our diet should reflect the sensibilities of this nutritional niche: lean meats; fish; seafood; low glycemic vegetables and fruit, (modern agriculture has significantly increased the sugar and starch content of vegetables and fruits over their Paleolithic counterparts), nuts and seeds - the evolutionary diet.
The term glycemic index, (GI) (a qualitative indicator of carbohydrate's ability to raise blood glucose levels), has seen a lot of mileage among the many non-ketogenic low carbohydrate diets. Most of these diets attribute the rise in obesity to the over consumption of high glycemic carbohydrates, and the subsequent over production of insulin.
While this may be an oversimplification, there is growing evidence to support a relationship between GI and non-insulin dependent diabetes (NIDDM), and obesity. In a prospective study of 65,000 US women, researchers were able to demonstrate that the dietary GI was positively associated with the risk of NIDDM.
The authors concluded that diets with a high GI increase insulin demand and thus cause hyperinsulinemia among patients with NIDDM, as well as in normal subjects. If chronic, this hyperinsulinemia can increase the risk for, as well as exacerbate NIDDM.
The issue of carbohydrates and insulin has more recently been addressed in a review article by Grundy. Grundy states that because secretion by pancreatic beta-cells is glucose sensitive, a high intake of carbohydrates has been reported to produce higher post prandial insulin levels. Moreover, it is possible that repeated stimulation of a high insulin output by high-carbohydrate diets could hasten an age-related decline in insulin secretion and lead to an earlier onset of NIDDM.
However, chronic hyperinsulinemia is not only associated with NIDDM, but is also related to a host of other medical conditions jointly known as Syndrome X. The constellation of disorders comprising Syndrome X include hypertriglyceridemia, increased LDL cholesterol, decreased HDL cholesterol, hypertension, hyperuricemia and obesity.
If high GI carbohydrates in fact contribute to chronic hyperinsulinemia as multiple studies suggest, they are likely to be causative of these other conditions as well. In addition to their role in hyperinsulinemia, studies have also linked high GI foods with overeating.
One study found an inverse relationship between satiety and both glycemic and insulin index. In another study,it was found that voluntary energy intake after a high GI meal was 53% greater than after a medium GI meal and was 81% greater than after the low GI meal. The authors concluded that a high GI meal promotes excessive food intake in obese subjects. The literature clearly points to a role of high GI carbohydrates in the development of insulin resistance and its subsequent disorders.
However, GI is obviously not the whole story. One researcher examined the insulin demand generated by isoenergetic portions of common foods. While some of the results were predictable, i.e., the fact that glucose and insulin sources were highly correlated, some were unexpected, i.e., some protein-based foods induced as much insulin secretion as did some carbohydrate rich foods. At first glance, these results seem confounding. However, if one looks at the broader function of insulin, they are consistent.
Insulin is not just responsible for glucose disposal, but for storage and uptake of multiple nutrients. Whether these other nutrients can result in a chronic hyperinsulinemic state, as seen with high GI diets, is not known; it is unlikely due to their compensatory effect on glucagon. The other major difference between the insulin response of other nutrients versus carbohydrate is their effect on blood glucose.
While protein and fat stimulate insulin response, their effect on glucose is minimal. This lack of effect on blood sugar is more than trivial difference. It actually may be the glycosylation of end organs (especially the pancreatic beta-cells) that ultimately leads to NIDDM and its associated conditions. Thus, while a hyperinsulinemic state is not desirable for human health under any circumstance, the combination of hyperinsulinemia with impaired glucose homeostasis is likely to prove even more deliterious.
While the current literature would support limiting the consumption of high GI foods, GI certainly does not provide the final answer. If one was to follow this concept literally (as some popular books suggest) one could argue that potato chips at a GI of 50-59% were more beneficial than carrots at a GIU of 90-99%.
A better way of looking at carbohydrates is to return to the principles of the "evolutionary diet." Robert Crayhon, M.S., author and champion of the "Paleolithic diet", divides carbohydrates into two basic groups, paleocarbs and neocarbs. Paleocarbs include vegetables, fruits and perhaps tubers. Neocarbs (carbohydrates introduced within the last 10,000 years or less), include grains, legumes, and especially flour products, which did not exist for most of human history.
The worst of the neocarbs include sugar and white flour products. If we follow the simple guidelines of restricting ourselves to paleocarbs, we will in general be eating fiber rich, nutrient dense, low glycemic carbohydrates, the best nature has to offer.
Another argument against carbohydrate restriction is based on epidemiological evidence, and the Pima Indians are frequently cited. The Arizona Pima Indians have received the attention of the medical community because of their prodigious rates of obesity, which is nearly 70% among the adult population. Along with the reputation of being one of the most obese people known, the Arizona Pima has a rate of diabetes 8 times the national average with nearly 50% of the adult population over 35 afflicted with this condition.
In spite of innumerable studies, examining the Pima from every imaginable vantage point, there has been no defining discovery explaining the Pima's plight. One hypothesis favored by Eric Ravussn, Ph. D, is that after generations of living in the desert, the only Pima who survived famine and drought were those highly adept at storing fat in times of plenty. These "thrifty" genes which once ensured the Pima's' survival are now at the root of his demise.
Although it is not known for certain what metabolic processes these "thrifty" genes control, insulin resistance and glucose homeostasis are thought to be at the heart of the matter. Since preagricultural, man's diet was primarily derived from animal sources (protein/fat), an insulin resistant genotype would have minimized glucose utilization and thus, proven to be of an evolutionary advantage.
As primitive peoples have become acculturated and have assumed a modern diet, the constant supply of highly refined, high glycemic index carbohydrates has resulted in postprandial hyperinsulinemia and the subsequent diseases associated with this condition i.e. obesity, diabetes, cardiovascular disease, etc.
The Arizona Pima's diet prior to acculturation was essentially that of a hunter-gather with some subsistence farming: (chollacatus buds, honey mesquite, poverty weed, prickly pears, mule deer, white-winged dove, black-tailed jackrabbit, squawfish, and they raised wheat, squash and beans). However, by the end of the second World War, the Pima had almost entirely left their traditional lifestyle and adopted the typical American diet.
There are many problems with the typical American diet, and to blame the Pima's situation on just one element of that diet would be disingenuous. However, given the current scientific and anthropological studies, one could suggest that the high availability of sugar and highly refined, high glycemic carbohydrates (i.e. neocarbs), are at the core of the Pima's health crisis. It could also be extrapolated that, while the Pima's "thrifty" genes may work at a more accelerated pace, it is the same set of genes interacting with the same diet and producing the same results in the average American.
In 1991, the Pima's story became even more interesting. Peter Bennett FRCP, the lead epidemiologist studying the Arizona Pima, discovered in Sierra Madre, Mexico, the remnants of a tribe that once comprised the Southern half of the Pima Nation. However, unlike their Northern brothers, the Mexican Pima remained, in general, unacculterated and living a traditional lifestyle.
Also, unlike their northern counterparts, the Mexican Pimas were not obese, nor did they share in the Arizona Pima's high rate of diabetes and degenerative diseases. This dichotomy has been termed the "Pima Paradox." Since the Mexican Pima consume a diet comprised mostly of beans, potatoes, corn tortillas and the occasional animal product, (i.e. chicken) , this has often been used as the epidemiological case study for the benefit of high carbohydrate diets in obesity management.
However, two issues confound this example. First, on average, the Mexican Pima's have 23 to 26 hours/week of occupational physical activity versus the Arizona Pima's 5 hours or less. Certainly, such high levels of activity could mitigate the hyperinsulinemic effects of the Mexican Pima's diet.
The second issue is the "Enigma" within the "Paradox". Although the Mexican Pima does not have the health issues of the Arizona Pima, they still have a prevalence rate of diabetes at 6.4% (approximately 1.5x greater that the non Pima Mexicans), and a 13% incidence of obesity among the adult population.
While these numbers are impressive compared to the US population, and stellar compared to the Pima population, the question remains why should an essentially unacculturated population performing on average 23-26 hours of physical labor per week have any incidence of diabetes or obesity.
When modern day hunter-gatherers were studied by anthropologists, incidence of these conditions were non existent, even among the eldest members of tribe. The "evolutionary diet" model would thus suggest, in spite of their improved health over the Arizona Pimas, the Mexican Pimas are still consuming a less than optimal diet.
Although conclusions drawn from epidemiological data can sometimes be misleading, the real message that can be taken from the Pimas is that as a species we have proclivity towards obesity, a proclivity that will vary based on our genetic stock.
This genetic predisposition, while multifactorial in nature, probably centers around insulin resistance and glucose homeostasis. Since our preagricultural ancestors did not have ready access to simple carbohydrates, fats were the preferred source of caloric energy, and glucose conservation was evolutionarily advantageous.
In modern times, the detrimental combination of low physical activity, hypercaloric intake, and over consumption of neocarbs is at the root of our obesity crisis. A return to an evolutionary based diet - lean meats, seafood, fish, vegetables, fruits, (raw) nuts and seeds and moderate physical activity, will ultimately be the cure.
Health Risk Associated with reduced Carbohydrate Intake
Another argument against carbohydrate restriction focuses on the purported health risk of this dietary approach. Of the three macronutrients, protein, fat and carbohydrate, it is only carbohydrate that is nonessential to the human diet. Humans can exist for extraordinarily long periods of time without carbohydrate consumption as long as essential protein and fat needs are met. It is thus perplexing why nutritional dogma ascribes so many risks to the restriction of this non-essential nutrient.
Ketosis is a natural physiologic state induced during prolonged states of decreased glucose availability. It is triggered by severe coloric restriction or when carbohydrate intake falls below 20-30 grams, (most of the current low carbohydrate diets are nowhere near this level of restriction).
In ketosis, a set of elaborate metabolic processes occur which have the net result of decreasing insulin secretion, increasing glucagon secretion, switching off glycolysis, turning on lipolysis, switching muscles from glucose to almost entirely fatty acids for fuel, and ultimately providing ketone bodies (produced in the liver), markedly diminishing the need for glucose by the brain in particular and the body in general.
Ketosis was an absolutely vital survival mechanism for early man. It allowed him to survive periods of starvation as well as long periods of carbohydrate deprivation. Despite the role ketosis plays in normal human physiology, its' modern application has often been portrayed with multiple negative health connotations.
However, both scientific and epidemiological data has failed to justify these concerns. The ketogenic diet has been used for nearly 70 years to treat refractory seizures in the pediatric population. Multiple recent studies have described nutritionally balanced, food varied versions of this diet.
One investigator looked at the health profiles of adults who had been treated during childhood with ketogenic diet. He found no evidence of adverse effects on cardiovascular function, including arteriosclerosis, hypertension or cardiac abnormalities. Blood cholesterol determinations were performed on these adults and all were normal. These studies thus fail to reveal any short term complication or long term sequelae associated with ketogenic diets.
In the mid twenties to late thirties, the famed anthropologist V. Stefansson chronicled the life and culture of the Eskimo in a series of books and journal articles. Of the many observations made by Stefansson, he was most intrigued with their diet and health. In spite of a nearly 100% animal based diet, the Eskimo people enjoyed an excellent state of well being and a freedom from many western diseases.
This observation was greeted with a high degree of skepticism in a scientific community that was becoming increasingly hostile toward the role of protein and fat in the American diet. To silence his critics, Steffansson devised a study whereby he would consume an all meat diet for one year.
Under observation at Bellvue Hospital in New York City, Stefansson and a colleague did in fact consume for one year an all meat diet. At years end, to the surprise of the scientific community, both investigators were in excellent health. They demonstrated weight loss with reduction in body fat, normal kidney and liver function, and improvement in blood lipids (within the limits of diagnostic testing of the time).
The "Bellvue ward study" created quite a stir in the scientific community and was detailed in numerous articles appearing both in popular and professional literature. Although long term commentary cannot be made, this remarkable study certainly speaks to the short term safety of a ketogenic diet. Ample scientific, epidemologic and anthropological data exists to support the general safety of a ketogenic diet. However, this data does not exonerate all the modern inceptions of this diet.
Traditional cultures who consumed a largely animal based diet, derived a great deal of their vitamins and nutrients by consuming the organs, eyes, glands and gonads of their prey. Modern ketotic diets are primarily based on common American foods, i.e. meats, eggs and cheeses. They do not qualify the source of animal products (i.e. salmon versus bacon), and are usually overloaded with salt. In general, these diets are only concerned about limiting carbohydrate intake without overall regard to food quality.
In the most popular version of the ketogenic diet, Dr. Atkins New Diet Revolution, Dr. Atkin's writes "at the other end of the spectrum is a convenience food that sounds terrible fatty, but in fact, contains nearly none. Those are the maximizers of crispness - fried pork rinds - the zero carbohydrate consolation prize for corn or potato chip addicts. Virtually all the fat has been rendered off, leaving you with the protein matrix that held the pork fat together. Your pate, sour-cream based dips and guacamole find an exceedingly crisp and comfortable home atop a fried pork rind.
In spite of their potential physiologic benefits, the modern ketogenic diets with their unbalanced, nutrient poor and often absurd dietary suggestion are difficult to support. However, ketogenic diet based on evolutionary appropriate foods would be interesting to pursue in clinical practice.
Lack of fruits, vegetables and grains Aside from the ketogenic diets, most other reduced carbohydrate programs allow for the ample consumption of vegetables and the modest consumption of low glycemic fruit, (the best sources of nutrients and phytonutrients available to man).
Of the major carbohydrate sources mentioned, only grain is heavily restricted. Although present diet dogma portrays grain as the quintessential food source, (it is at the base of the food pyramid after all), many nutritional scientist have called this assertion into question. In a work of prodigious proportions (342 literature citations), Dr. Loren Cordain examines mans double edged relationship with grain.
On one hand man is utterly dependent upon grain as a primary caloric source and yet grain may be at the core of many of our common maladies. As would be predicted by the evolutionary diet model, Dr. Cordain concludes that grain is biologically novel to the diet of mankind as it was introduced as a staple food only 10,000 years (or less) ago. Due to its relatively recent introduction, our species has not fully adapted physiologically to its digestion and metabolism.
In spite of the impressive nutrient profiles of grain, the vitamins and minerals often occur in forms that have low bioavaildality to the human digestive tract. In addition to these poorly utilizable nutrients, grain contains many secondary metabolic components commonly categorized as anti-nutrients.
Anti-nutrients are chemical compounds naturally occurring in grains, which evolved to protect the plants from predators. Processing and cooking does not not fully rid the grain of these elements, thus making them prominent in our diet. Recent scientific study has linked these anti-nutrients to a number of negative biological consequences which include: allergen based disorders; pancreatic hypertrophy and disruption of the gut cell wall tight junctions (thus exposing the systemic circulation to food allergens and gut flora).
One of the most curious of these negative processors associated with grain anti-nutrients is a phenomenon known as molecular mimicry. Molecular mimicry is when a similarity of structure is shared by products of dissimilar genes. When this phenomenon occurs within the human body, the potential for developing an autoimmune reaction is created.
The main body of evidence implicates viral and bacterial pathogens as initiators of cross-reactivity and autoimmunity. However, there is an emerging body of literature supporting the view that dietary antigens including cereal grains may also induce cross-reactivity and hence autoimmunity by virtue of peptide structures homologous to those in the host.
The diseases that may share this common origin are numerous and varied. They may include everything from aphthous ulcers (canker sores), to rheumatoid arthritis to non-insulin dependent diabetes to multiple sclerosis. While many of these assertions may seem preposterous to a society reared on grain, evolutionary pressures would suggest otherwise. The primate gut was initially adapted to both the nutritive and defensive components of dicotyledonous plants rather that the nutritive and defense components of mono- cotyledons cereal grains.
Consequently, humans, like other primates, have had little evolutionary experience in developing a physiology that can both fully utilize and defend against the compounds which naturally occur in cereal grains. So, while the motives for limiting grains may be completely unrelated, many of the popular incarnations of reduced carbohydrate diets may be paying their readers a great - albeit - indirect service.
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