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“The problem [is] that the tissues of Western populations [are] awash in omega-6s, fats that compete with the omega-3s.” THE QUEEN OF FATS, Susan Allport (University of California Press, 2006)
Harvard Study Says: EAT FISH
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The Obesity Connection
A federally-funded study by Harvard Medical and Public Health researchers, led by Dariush Mozaffarian, MD, DrPH, and Eric B. Rimm, ScD, analyzed years of data and concluded that the health benefits of eating fish far exceed the potential risks from contaminants. (Journal of the American Medical Association, October 18, 2006) They determined that the cardiovascular health benefits of wild-salmon consumption, for example, outweigh the cancer risks by 900 to one, while the benefit of farm-raised salmon outweigh the risk by 300 to one. The Harvard review found that people who eat one or two servings of fish per week, especially fatty varieties such as wild salmon, may reduce their risk of death from heart attack by 36% and overall mortality by 17%.
In her book Queen of Fats (University of California Press, 2006), science writer Susan Allport tracks the long and winding road that brought us to this point—it’s a detective story of epic proportions (which she skillfully condenses into less than 200 pages). It starts in the 1970s when Danish physicians Hans Olaf Bang and Jorn Dyerberg went to Greenland to investigate Eskimos who ate large amounts of seal and whale blubber, without suffering from heart disease. Fat was thought to be “the dietary demon that causes this disease.”
I can’t tell the whole story here, of course, but I can whet your appetite with a few of the high points, including the obesity connection.
Blubber Beats Heart Disease
After much research and planning, and a long trip, some of it by sailboat, Bang and Dyerberg persuaded 130 Eskimos, 61 men and 69 women, who lived by fishing and hunting, to allow their blood to be tested. Among other things, the doctors wanted to know if their blood lipids would match their high fat consumption. “If the answer was yes,” Allport writes, “then the power of blood lipid levels to predict heart disease would be put in question; if no, then widely accepted recommendations to reduce intake of fat, especially animal fat, would be undercut.” Bang and Dyerberg would have a scoop either way, given that the Eskimos had a very low incidence of heart disease.
Tests on the spot showed that the Eskimos had low levels of all of the lipoproteins, except HDL. [The specimens were also frozen and taken back to Denmark for further testing.] “This outcome was not surprising, given the Eskimo’s low incidence of heart disease, but it was surprising in light of their diet rich in animal fat and cholesterol,” Allport explains. “Moreover, it seemed to be the result of dietary rather than genetic differences, since Eskimos living in Denmark had lipid profiles resembling those of Danes.”
Their paper in the Lancet reporting these findings, which Dyerberg says was a mere curiosity when published, has since become a nutrition classic-- mainly because it was the first to record high levels of HDL-cholesterol, now known as “good cholesterol,” in people with a low incidence of heart disease.
Even more important, as Allport sees it, was their suggestion that the explanation was “probably the large amount of polyunsaturated fatty acids in the fat tissue of the animals eaten.” At the time, polyunsaturated fatty acids were known to prevent increases in blood cholesterol, but nothing was known about the fats of most fish and marine animals. The suggestion was their "guess" based on the fats in fish that had been analyzed, such as salmon, and on a belief that “the composition of animal fatty tissue changes more and more in the polyunsaturated direction as the temperature of the medium in which the animal lives decreases.”
The Danish researchers didn’t stop there, however. They went on to analyze the 130 frozen samples they had brought back from Greenland to determine the basic building blocks of the lipids in the Eskimos’ blood. Comparing the lipid make-up to that of Danes, they found “a striking difference in the two populations,” Allport writes.
The Eskimo blood contained a very small amount of arachidonic acid--an offspring of linoleic acid, the only fat known at the time to be essential for human health--and a very large amount of a fatty acid they were unable to identify. “The Eskimos had seven times as much of this mystery fat as did Danes, and about one-seventh the amount of arachidonic acid.”
Determined to identify the mystery fat, it was decided that Dyerberg would fly to the United States to consult with Ralph Holman, a world authority on the composition and function of fats. Holman quickly identified the substance as eicosapentaenoic acid (EPA), and a smaller amount of another fatty acid known as docosahexaenoic acid (DHA), which was also present in larger amounts in Eskimos than in Danes.
Dyerberg left Holman’s lab knowing that eicosapentaenoic acid (EPA) was important, but it took another chapter in the mystery to determine how important. This time the key player was Ralph Holman. (To give you a hint, arachidonic acid is a member of the omega-6 family, and EPA and DHA belong to the omega-3 family.)
Ralph Saves Shawna
This episode starts with the tragic death of Ralph Holman’s mother. She was hospitalized for a condition that destroyed her bowels in the early days of intravenous feeding. Fat being insoluble in water, the first intravenous solutions were fat free. Patients required to be on them for long periods did not do well.
As noted above, linoleic acid was known to be essential for human health; it could not be produced internally and had to be provided in the diet. Holman suspected that other fatty acids might be critical as well. “His mother’s doctor was receptive to what Holman was telling him about fatty acids (as many doctors at the time were not),” Allport relates, “but neither of them could figure out how to safely provide her with the nutrients she was missing.” A nontoxic fat emulsion was developed shortly thereafter, but it was too late for Holman’s mother.
Driven by the loss, Holman redoubled his efforts to learn more about essential fats and convince the medical profession of their importance. When the next life-or-death situation came along, informed by Bang and Dyerberg’s work with Eskimos and other developments, Holman was ready. (Holman’s mother died in 1962, a decade before Bang and Dyerberg went to Greenland.)
In 1979, Holman was asked to consult in the case of a gunshot victim, a six-year-old girl, who had been accidentally shot in the stomach. “Shawna Renee Strobel was a blond, blue-eyed, healthy kindergartner at the time she suffered the wound that would make her the first human case of omega-3 deficiency ever to be recorded in the scientific literature,” Allport writes.
So much of Shawna’s intestine and colon were removed that she had to be fed intravenously. Unlike the case of Ralph’s mother, linoleic acid was included in the IV. Shawna did well for almost a year, but “then she began having episodes of tingling, numbing, and weakness in her legs, sometimes accompanied by blurred vision and a total inability to walk,” Allport relates. “It was a peculiar array of symptoms that the neurologists treating her had never seen before.”
Fortunately, one of her physicians, Terry Hatch, suspected that her intravenous nutrition might be the problem. Ralph Holman was called in to do a fatty acid analysis of Shawna’s blood.
“Holman never met Shawna or her mother, but he saved the Illinois girl’s life when he determined that the amount of omega-3 fatty acids in the girl’s serum was about one-third that of controls,” Allport writes. Holman also determined that her intravenous preparation was very low in omega-3 fatty acids. He suggested that she be switched to a preparation “based on soybean oil and containing both linoleic and alpha linolenic acids (in a ratio of 6 to 1),” Allport explains. “In twelve weeks, all of her neurological symptoms had disappeared.” (Alpha linolenic acid (ALA) is the parent of the omega-3 family and the precursor of EPA and DHA, which Bang and Dyerberg found in abundance in the blood of Eskimos.)
Dr. Hatch, who in 1982 joined with Holman to publish their findings about the young gunshot victim in the American Journal of Clinical Nutrition, told Allport he didn’t think the case “made a lot of impact.” Nevertheless, Allport writes, “For Holman and a few other researchers, Shawna’s case brought a sea change in attitudes, a new way of looking at the world.” It meant that omega-3 deficiency could impact, perhaps cause, heart disease and neurological disorders, even obesity.
The Obesity Connection
In Challenge Yourself, I wrote about a study, reported in the December 1996 issue of Metabolism, where Japanese researchers raised mice prone to diabetes and obesity on a variety of diets containing 60% fat, and then measured the change in body weight. All of the diets contained the same number of calories; the only difference was the type of fat consumed. The variation in weight gain was truly startling. According to Artemis P. Simopoulos, MD, author of The Omega Plan (Harper Collins, 1998), the difference in weight between the mice fed soybean oil and those fed fish oil was “comparable to the difference in weight between a 225- and a 150-pound man.” A lard/fish oil comparison produced a weight gain disparity almost as great, according to Dr. Simopoulos.
Simopoulos (who Allport recognizes as an authority on fats) observed that soybean oil and lard are high in omega-6 fats and that fish oil is high in omega-3s, but offered no further explanation for the discrepancies in weight gain. Susan Allport, however, offers a detailed and plausible explanation in Queen of Fats.
The following is my “Cliff Notes” version.
She cites research indicating that there “are profound differences between diets and tissues full of omega-6s and omega-3s, differences that slow our bodies down and speed them up.” To explain this idea, scientists have developed what they call “the pacemaker or the leaky membrane hypothesis.”
Analyzing the tissues of animals with different metabolic rates, researchers have found that “the fats of large, slow mammals were more saturated and contained more omega-6 fatty acids than the fats of small, fast mammals like the mouse, which contains more DHA,” Allport writes. “The fats of high-speed animals like the hummingbird were loaded with DHA.” As noted earlier, DHA is a member of the omega-3 family.
The high amounts of DHA result in leakier cell membranes—membranes that have to work harder to maintain their integrity. “A membrane needs to be cohesive enough to be a barrier, but fluid and disordered enough so that the proteins, enzymes, and receptors that are imbedded in it can move around freely and do the things they need to do,” one of the researchers explained. “They have found it is the DHA concentration of membranes that correlates most closely with an animal’s metabolic rate,” she adds.
Metabolism is controlled by genetic factors, but diet also plays a part, which includes the amount of omega-6s and omega-3s an animal eats.
Allport tells us that obesity expert Leonard Storlien, PhD, was perhaps the first person to see the connection between the pacemaker theory and problems associated with energy balance and obesity. “If you have a person running at a metabolic rate that is 40 percent of someone else,” Storlien told Allport in a phone interview, “you would have a profound predisposition for obesity.”
“Storlien had already found that rats do develop insulin resistance on diets that were rich in either saturated fats or omega-6s,” Allport writes. “But fish oil was different. It protected against both insulin resistance and obesity.” This was true in rats, but what about humans?
Storlien knew that the fish-eating Eskimos studied by Bang and Dyerberg had a very low rate of diabetes, and when he heard about the pacemaker or leaky membrane theory immediately saw the “implications for understanding the cluster of diseases surrounding energy and insulin resistance in humans.”
Storlien and a group of other researchers looked to the Pima Indians of Arizona, who have the highest incidence of type 2 diabetes in the world, for another human example, “and found half the amount of DHA in the phospholipids of their skeletal muscles as in a group of Australian, largely Caucasian, men,” Allport relates. “Skeletal muscle is the major site of glucose uptake in the body, and this difference in DHA content was closely correlated with the Indian’s insulin resistance.”
Insulin resistance causes the Pimas to store fat (glucose that isn't burned by their muscles is deposited as fat), which is a good thing when food is scarce and unpredictable, but detrimental when food is abundant. “This is a transition that the Pima Indians have recently made,” Allport observes. Widespread obesity, regrettably, comes with their newfound abundance.
Unfortunately, neither Storlien nor anyone else has been able to demonstrate improvement in insulin sensitivity among type 2 diabetics after omega-3 fatty acids in their diets are increased. “It’s driven most of us nuts,” Storlien told Allport. “It happens so easily in animals. Why doesn’t it happen in humans?”
The probable reason is that obese people carry huge fat reserves. “It would take years to turn over all of the fats on an obese person [from omega-6 to 3],” Storlien told Allport. “I haven’t been able to run my studies out that far. You don’t get grants to do long-term intervention studies.”
Interestingly, he’s had difficulty publishing a one-year study in which a high omega-3 diet did produce “an impressive improvement in insulin action” and other variables. “This study was rejected by five journals,” Storlien told Allport. “Not because of the science, but because the reviewers said, ‘You couldn’t possibly get theses effects from just changing the fatty acid profile of the diet.’”
Metabolism is not a simple matter, Storlien understands. He acknowledges that activity level and calorie intake and many other factors contribute to diabetes and obesity. “But the pacemaker theory is a matter of a number of mechanisms coming together to push metabolism in a particular direction,” he told Allport, “and it’s time to test it with well-funded, long-term studies.”
In the meantime, Allport agrees with the Harvard researchers: Eat Fish. She also recommends eating lots (and lots) of fruits and vegetables. Green vegetables, she says, are “full of alpha linolenic acid, the parent omega-3 fatty acid.”
[For many more details, and suggestions on how to put omega-3s back into your diet, read Susan Allport’s THE QUEEN OF FATS. (Omega-6 fats are the king, because they were the first to be found essential to human health.) You’ll find it on Amazon.com and probably at your local bookstore.]
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