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Deep-Frying Blocks the Heart Benefits of Fish
11/19/2009
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Findings echo earlier reports that fish fried in vegetable oil loses most of its omega-3 benefits

by Craig Weatherby and Randy Hartnell


This week's widespread coverage of a study presented at an American Heart Association scientific conference confirms two things.


First, deep-fried fish is bad for your heart, while baked, broiled, and boiled fish are good for it.


Key Points

  • New study confirms prior findings that fried fish undermines hearth health.
  • The white fish most often served fried have inferior fat profiles, and the omega-6 fats in deep-fryer oils are seriously damaged by high frier temperatures.
  • Baked, broiled, and boiled fish are much healthier than fried fish.
  • Adding low-sodium soy sauce enhanced fish-eaters’ heart health.

Second, the media reports confirm that most news organizations suffer from short-term memory syndrome… accompanied by a bad case of no-context disorder.


Many media outlets reported on the new population study, in which University of Hawaii researchers looked for links between heart health and different cooking methods for fish.


Those who reported eating mostly baked or boiled fish enjoyed good heart health outcomes.


In contrast, those who reported eating mostly fried fish suffered below-average heart health outcomes.


Media outlets hungry for fresh content spread the news fast… but the “new” findings were actually old news.


That’s okay, though it would have been valuable for people to know that the Hawaii-based study simply echoed similar findings published over the past several years.


What’s really unfortunate is that reporters made no attempt to explore or explain the study’s outcomes... even though the likely reasons hold serious implications for the impact of Americans’ diets on their heart health.


Study details

Researchers led by Lixin Meng, M.S. analyzed the diets and medical records of 186,000-plus people over a 10-year period (Meng L et al. 2009).


The participants were 186,127 men and women of African-American, Caucasian, Japanese, Native Hawaiian and Latino descent, aged 45 to 75 years and living in Hawaii or Los Angeles County, with no history of heart disease.


Ms. Meng’s team divided them into groups, depending on the subject’s reported intakes of canned or fresh fish, and according to the fish preparations people ate most oftenraw, baked, boiled, fried, salted or dried.


As we’ve said, the analysis showed that those who reported eating mostly fried, salted, or dried fish had below-average heart health.


Regular consumption of salted or dried fish was also linked to below-average heart health after 10 years.


But folks who enjoy our smoked fish needn’t be concerned about moderate consumption. This is because salted fisha term applied to fish cured by salt alone, without smokingcontains levels of sodium much higher than most smoked fish.


And our Vital Choice brand smoked salmon and sablefish generally contain less sodium than national brands (and no nitrites or other commonly used preservatives).


Surprising to many, smoked salmon has even more omega-3s than fresh salmon. For more on that, see the reader Q&A in this issue.


As to the negative finding for dried fish, we suspect that most of the fish meeting that description on the survey had very few omega-3s, or was salted heavily.


What about the benefits of added tofu or low-sodium soy sauce? Lead author Lixin Meng made a reasonable speculation: “My guess is that, for women, eating omega-3s from shoyu [natural soy sauce] and tofu that contain other active ingredients such as phyto-estrogens might have a stronger cardio-protective effect than eating just omega-3s” (AHA 2009).


Broiling was left out, but found healthy in prior studies

For reasons not explained in the official summary, Ms. Meng’s team did not compare the participants’ heart health outcomes to consumption of broiled fish… a very common cooking method that was associated with good heart health outcomes in prior studies.


Like baked and boiled fish, broiled, grilled and pan-sautéed fish generally conveys little or no added vegetable oil to consumers… especially when compared to deep-fried fish, whose bread or batter coating literally oozes vegetable oil.


This decision by the Hawaiian team to exclude grilled and broiled fish from the analysis was a very odd one, since many Americans who eat fish broil or pan sauté it, and very few boil it.


We can only speculate that they included boiling as a cooking type because many residents of Hawaii and Los Angeles County are of Japanese or Korean descent, and people in those cultures eat most of their fish raw, steamed, or boiled in soups and stews.


“New” findings are old news

Starting six years ago, a Harvard team conducted three epidemiological studies in older adults, looking for differences in heart health based on various fish cooking methods.


Their findings linked enjoyment of even modest amounts of broiled or baked fish to enhanced cardiovascular health and reduced risk of stroke or death from heart disease… especially from heart arrhythmias (Mozaffarian D et al. 2003; Mozaffarian D et al. 2005; Mozaffarian D et al. 2006).


But like the new Hawaiian study, all three Harvard investigations linked fried fishsuch as fish sticks and the breadedor battered fillets in fast-food sandwichesto worse results on tests of cardiovascular health factors… and to higher rates of stroke and heart-related death.


Why is fried fish bad? Blame the omega-6 fats in deep-fry vegetable oils

There are two rather obvious reasons why fried fish doesn’t seem to improve hearth health and may even worsen it.


First, the white fish used in sticks and fast-food sandwiches are relatively low in omega-3s, which exert anti-inflammatory, anti-arrhythmia, and other heart-helping effects… but that alone wouldn’t explain worse heart health outcomes.


Also, the farmed white fish commonly used for fried filletslike tilapia and catfisheat grain-based diets that give them much higher in omega-6 levels than their wild counterparts (see “Farmed Fish Possess Unhealthful Fat Profiles” and “Inflammation Free Diet Book Puts Wild Salmon on a Pedestal”).


Instead, the problem with deep-fried fish lies in the omega-6 fatty acids that predominate in the vegetable oils food companies use to fry breaded fish (e.g., soy, safflower, sunflower, and cottonseed oils).


The omega-6 fat that’s abundant in common frying oilscalled linoleic acid or LAexerts generally pro-inflammatory influences in the body, especially when the diet is overloaded with them. And chronic “silent” inflammation is a key driver of cardiovascular disease and diabetes.


While a recent American Heart Association science review found no link between excess dietary omega-6s and worse heart outcomes, many epidemiological and lab studies show that diets overloaded with “trans” omega-6 fats harm artery health and yield higher rates of heart disease.


(For more on this topic, see “Heart Association Appears Blind to Risks of America's "Omega-Imbalance"” and “Report Finds Americans Need More Omega-3s and Less Omega-6s.”)


Omega-3 and omega-6 fatty acids compete for a place in their hosts’ cell membranes... and because fried fish is loaded with omega-6s, fewer of the omega-3s in it will end up in its consumers’ cell membranes, compared with the omega-3s in raw, baked, boiled, steamed, or broiled fish.


Worse, frying oil at temperatures above 350° F (180° C)which is standard in fast food chainsproduce unhealthy changes in polyunsaturated fatty acids, including the omega-6 fats in vegetable oils.


Oils chemist Ted Miller (see “Fish Oil Pioneer Picks Vital Choice Salmon Oil”) has warned us about the negative health effects that deep-frying produces in vegetable oils… a warning supported by numerous studies (Velasco J et al. 2004; Choe E et al. 2007; Marmesat S et al. 2008).


Ted spent 40 years in the menhaden industry, and found that omega-3s remain relatively stable up to about 350° F. He said that they tried feeding fish oil cooked at temperatures above about 350° F to chickens, and it stunted their growth.


And until recently, a very large proportion of the omega-6s in fried foods occurred in the undesirable trans form that raises the risk of atherosclerosis and makes blood “sticky”… two key factors that promote cardiovascular and ischemic stroke.


Fortunately, new laws are forcing trans omega-6 fatscreated by partial hydrogenation of vegetable oilsfrom fast-food chains’ deep fryers and from packaged foods.


It seems likely that if the Hawaiian and Harvard studies were repeated now, the heart-health signs and outcomes of people who report eating mostly fried fish wouldn’t be quite as bad.


Nonetheless, the overload of overcooked, damaged omega-6 fats present even in fried fish made with non-hydrogenated oils would in its place as the worst choice.



Sources

  • American Heart Association (AHA). How fish is cooked affects heart-health benefits of omega-3 fatty acids. Abstract 1404/Poster 2071. American Heart Association Scientific Sessions 2009. Accessed at http://americanheart.mediaroom.com/index.php?s=43&item=862
  • Choe E, Min DB. Chemistry of deep-fat frying oils. J Food Sci. 2007 Jun;72(5):R77-86. Review.
  • Marmesat S, Velasco J, Dobarganes MC. Quantitative determination of epoxy acids, keto acids and hydroxy acids formed in fats and oils at frying temperatures. J Chromatogr A. 2008 Nov 21;1211(1-2):129-34. Epub 2008 Sep 30.
  • Meng L, Wilkens L, Kolonel L. Abstract 1404: Fish Consumption and Ethnic Differences in Coronary Heart Disease Mortality in a Multiethnic Cohort. Circulation, Nov 2009; 120: S498. Accessed at http://circ.ahajournals.org
  • Mozaffarian D, Gottdiener JS, Siscovick DS. Intake of tuna or other broiled or baked fish versus fried fish and cardiac structure, function, and hemodynamics. Am J Cardiol. 2006 Jan 15;97(2):216-22. Epub 2005 Nov 21.
  • Mozaffarian D, Lemaitre RN, Kuller LH, Burke GL, Tracy RP, Siscovick DS; Cardiovascular Health Study. Cardiac benefits of fish consumption may depend on the type of fish meal consumed: the Cardiovascular Health Study. Circulation. 2003 Mar 18;107(10):1372-7.
  • Mozaffarian D, Longstreth WT Jr, Lemaitre RN, Manolio TA, Kuller LH, Burke GL, Siscovick DS. Fish consumption and stroke risk in elderly individuals: the cardiovascular health study. Arch Intern Med. 2005 Jan 24;165(2):200-6. Erratum in: Arch Intern Med. 2005 Mar 28;165(6):683.
  • Velasco J, Marmesat S, Bordeaux O, Márquez-Ruiz G, Dobarganes C. Formation and evolution of monoepoxy fatty acids in thermoxidized olive and sunflower oils and quantitation in used frying oils from restaurants and fried-food outlets. J Agric Food Chem. 2004 Jul 14;52(14):4438-43.

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