MONTREAL—With the billions of dollars spent over the last 2 decades on clinical trials investigating dietary lipids and the ways in which to best control them, you would think most of the major questions would have been resolved by now. Not so. Just ask any attendee at the recent biennal meeting of the International Society for the Study of Fatty Acids and Lipids.
Name your lipid and it seems there are a host of scientists willing to queue up to argue its pro’s and con’s for human health. The exceptions are the omega-3 fatty acids: almost everyone agrees they are good.
The Omega Fat Balancing Act
On the cardiovascular disease front, the rampant incrimination of saturates, trans fatty acids, and cholesterol that characterized an earlier epoch in lipid research, is giving way to the canonization of the omega fatty acids.
To be sure, saturates remain cardiovascular villains, exceeded in danger only by trans fatty acids, according to Walter Willett, MD, Chair of the Nutrition Department at the Harvard School of Public Health. Trans fatty acids are formed mainly from the partial hydrogenation of vegetable oils used to make margarines and shortenings, and from a cardiovascular viewpoint, they’re none too good.
But long chain omega-3’s, mainly EPA and DHA from fatty fish, have stolen the lipid research limelight. Dr. Willett acknowledged the cardiovascular benefits of both omega-6 and omega-3 fatty acids. However, he asserted that, “the ratio of omega-3 to omega-6 fatty acids does not appear to be related to risk of coronary heart disease, and efforts to raise this ratio by reducing omega-6 fatty acid intake are likely to increase mortality.”
This provocative statement overlooks the mounting evidence from observational, clinical, animal, and biochemical studies that excess consumption of omega-6s contributes to heart disease by promoting thrombosis, and increasing inflammatory responses and arrhythmias.
USDA data from the most recent Continuing Survey of Food Intakes by Individuals, 1994–1996, show clearly that the omega-6 fatty acid, linoleic acid, represents 88% of all polyunsaturates consumed by Americans. In contrast, long chain omega-3 fatty acids account for less than 1% of all polyunsaturates, and alpha-linolenic acid, the only omega-3 fatty acid in plants, accounts for about 9%. Dr. Willett’s assertion not withstanding, most fatty acid researchers contend that the gross imbalance between omega-6s and omega-3s is harmful for most people. While consumption of fish and fish oil supplements is on the rise, there is clearly a long way to go to adjust this imbalance.
Plants versus Fish
There is an emerging consensus that increased consumption of omega-3 fatty acids is a good move. But the relative merits of plant-derived versus fish-derived omega-3s continue to elicit controversy. Alpha-linolenic acid (LNA) the 18 carbon omega-3 fatty acid in flax, canola, and walnut oils is considered beneficial, but not equivalent to EPA and DHA. Stephen Cunnane, PhD, Professor of Nutrition at the University of Toronto, presented elegant studies using 18-carbon fatty acids to show in neonatal rats that, “Beta-oxidation consumes about 90% of a physiological dose of 13C-LNA within 48 hours.” This means little LNA is available for conversion to long chain DHA. In women given one of four 13C-18-carbon unsaturated fatty acids, label uptake into plasma triglycerides decreased with increasing unsaturation. Thus, incorporation of LNA with three double bonds was less than linoleic acid with two.
Similarly, adipose tissue incorporation of both linoleic and LNA was less than for oleate or elaidate, each with one double bond. These observations show that polyunsaturated fatty acids are less likely to be stored than monounsaturates. Graham Burdge, MD, and colleagues, University of Southampton, showed that increasing the availability of LNA did not enhance its conversion to EPA. However, Wes Alexander, MD, University of Cincinnati, reported that renal allograft patients whose therapy included arginine and canola oil, rich in LNA, had fewer rejections and one fourth the likelihood of developing diabetes compared with patients on standard treatment without arginine and canola oil.
It appears that fresh fish remains the best source of omega-3s. Claudio Galli, PhD, Professor at the Institute of Pharmacological Sciences, University of Milan, reported that the bioavailability of omega-3s from fish itself is greater than from capsules. This may be related to the higher surface to volume ratio of the omega-3s when present in lipid membranes, as occurs in foods. Dr. Galli noted that 300 mg omega-3 in fish is equivalent to twice the amount in capsule form. Plasma DHA levels, following the daily consumption of 308 mg DHA from smoked salmon were double those obtained with 1,680 mg provided as capsules. These observations may help explain why relatively small amounts of fish are effective in protecting heart health. Now, if they could do something about that cream cheese. …
Low Omega-3 Equals High BP
Andrew Sinclair, PhD, Professor of Food Science, Royal Melbourne Institute of Technology, was the first to report that in laboratory animals, omega-3s in the early developmental period affects blood pressure later in life. Moderate omega-3 deficiency in the perinatal period resulted in hypertension and anomalous brain fatty acid composition, despite reversal of the deficiency long before blood pressure was measured. Dr. Sinclair suggested that omega-3 intake during a critical developmental period may affect long term regulation of blood pressure.
In overweight human hypertensives on a weight loss diet, Trevor Mori, PhD, Department of Medicine, University of Western Australia, found that daily fish consumption improved glucose and insulin metabolism and blood pressure compared with eating no fish. Even without weight loss, fish consumption resulted in greater improvement in blood pressure compared with eating no fish.
In a separate study, Dr. Mori examined the effect of omega-3 on oxidative stress, by measuring urinary F2 isoprostane excretion, a sensitive measure of lipid peroxidation. In type 2 diabetics who consumed 4 g/day EPA, DHA, or olive oil, urinary F2 isoprostane excretion was reduced by about 20% with EPA or DHA compared with olive oil. Contrary to expectations that omega-3 consumption might increase oxidative stress, the fish oil actually reduced it. Rosemary Wander, PhD, Department of Nutrition and Food Service Systems, University of North Carolina, reported that in postmenopausal women on HRT, the formation of conjugated dienes in LDL and HDL decreased as the amount of fish oil increased. These results further indicate that high doses of fish oil do not increase the oxidative susceptibility of LDL and HDL.
If industrialized societies set the pace for developing heart disease and type 2 diabetes, the Arctic-dwelling Inuit show how to escape these scourges. Well, they did until recently. CVD, diabetes, obesity, and hypertension are increasing among the Inuit as their traditional marine diet is replaced by modern processed foods. Minnie Grey, of the Nunavik Regional Board of Health and Social Service, reported that “diabetes was practically non-existent 10 years ago in Nunavik and is now on the rise.”
Eric Dewailly, MD, Scientific Director of the Health and Environmental Group, Centre Hospitalier Universitaire de Quebec, Laval University, confirmed that the traditional diet high in omega-3s protects Inuit in northern Quebec and the James Bay Cree from CVD. Henning Pedersen, PhD, of the Center for Arctic Environmental Medicine in Greenland, estimated that the high level of omega-3s in the diet delays the onset of aortic thromboses in Greenland Inuit by 20 years. Laurie Chan, PhD, of the Center for Indigenous Peoples’ Nutrition and Environment, McGill University, Montreal, reported that Inuit in northern Canada consume an average of 32% of their energy from fat and that Inuit men and women consume, on average, 2.7 and 2.1 gm/day omega-3s, respectively. Consumption of EPA and DHA in the U.S. averages 0.2 gm/day, at best.
The traditional diet can protect Alaskan Inuit from developing type 2 diabetes reported Sven Ebbesson, PhD, Professor Emeritus at the University of Virginia. In a study of 44 Alaskan Inuit with excess body weight and impaired glucose tolerance, increased consumption of traditional foods like fish and seal blubber, and reduction of store-bought foods virtually eliminated progression to diabetes. After four years, not one of the 44 subjects developed type 2 diabetes, even though they did not lose weight. Participants with improved glucose tolerance had significantly higher plasma omega-3s and lower palmitic acid levels.
What About Toxins?
Environmental toxins in marine animal fats is a growing concern. Bente Deutch, PhD, of Aarhus University, Denmark, reported that blood omega-3 levels in Inuit from Eastern and Western Greenland correlated significantly with levels of organic pollutants. Seal and polar bear blubber were the primary contributors of both omega-3s and pollutants. Dr. Deutch noted that high blood PCBs “appeared to elevate triglycerides and overrule the beneficial effects of omega-3s.”
Concentration of methylmercury in certain sport fish is well known. Measurement of hair and blood mercury in sport fishermen before and after the fishing season in James Bay confirmed a significant increase in mercury. Nevertheless, the fishermen had significantly reduced VLDL cholesterol, apo B LDL, and oxidized LDL, noted Dr. Marie-Claire Belanger, of Canada’s Laval University. Exposure to methylmercury did not lead to an increase in oxidized LDL. The question of dose and total exposure is critical, but these studies suggest that overall, the benefit of omega-3s outweighs the risk associated with environmental contaminants. However, it is prudent to limit consumption of highly contaminated, larger, older fish and marine animals.
Fish Oils Build Better Brains
Presentations on omega-3s in fetal and infant development drew standing-room-only crowds. Dr. Susan Carlson, of the University of Kansas, showed that women who consumed an average of 7 DHA-enriched eggs/week during the third trimester had a 6-day longer gestation period than those consuming a similar number of unenriched eggs. Average birthweight increased 83 grams. While the difference was not statistically significant, it is highly suggestive.
Sheila Innis, PhD, Professor of Food, Nutrition and Health at the University of British Columbia, reported that in breast-fed infants, visual acuity was significantly related to red cell phospholipid DHA level at 2 and 12 months. Dr. Gerard Horntra and colleagues at the Department of Human Biology, Maastricht University, reported that visual acuity and other measures of visual information processing visual were faster at 8 years of age in those children with the highest DHA levels at birth. Although cognitive performance was unrelated to DHA status at birth, quality of motor movements was correlated with DHA.
DHA may also influence early language development. Dr. Innis’ group reported that plasma and red cell DHA content in breast fed term infants were related to vocabulary production and comprehension at 14 months. The ability to discriminate a non-native language consonant was related to plasma DHA at 9 months. The connection between long chain omega-3s and language development was also suggested from the work of Robert Katz, PhD, President of the Omega-3 Research Institute, who showed that in children with apraxia of speech, omega-3 supplementation improved the ability to produce meaningful sounds (see Holistic Primary Care, June 2002).
Deficits of both arachidonic acid (AA) and DHA are associated with suboptimal development of brain and neurological tissues, and of the vascular endothelium. Michael Crawford, PhD, Director of the Institute of Brain Chemistry and Human Nutrition, University of North London, pointed out that prenatally, the transplacental movement of AA to the fetus is greater than that of DHA. Unlike DHA, AA is a vascular relaxation factor. Dr. Crawford noted that its reduced availability in preterm infants raises the question of whether “inadequate supply of AA is responsible for failure of integrity in vascular growth.” Clearly, both AA and DHA must be available in adequate amounts for healthy fetal and infant development. Fortunately, those needs have been recognized by the FDA, which recently moved to eliminate regulatory barriers to the addition of these crucial fatty acids to infant formulas.