Sobering study finds unhealthful fat profiles in farmed tilapia and catfish; farmed salmon and trout test better, but still far from ideal
by Craig Weatherby
The startling results of a new study—in which scientists scrutinized the fat composition of farmed fish—ranks high among our most important health-science reports.
Thanks to continuous findings about the benefits of omega-3s, people are flocking to eat fish.
But the new findings suggest that many are making unhealthful choices, unwittingly.
The news flows from a revealing—and disturbing—new analysis of the fats found in four cheap, popular, farm-raised fish: Tilapia, Catfish, Salmon, and Trout.
The new research paper, from Wake Forest University, confirms and expands upon prior findings concerning the inferior fat profile and negative physiological effects of farmed Salmon.
Study puts focus on the key “omega-ratio”
Two kinds of dietary polyunsaturated fats are essential to human life and optimal health: omega-3 and omega-6.
And there’s no debate about two core facts:
- The proportion of omega-3 and omega-6 fats in people’s diets—which we call the “omega-ratio”—plays a major role in determining their current and future health.
- The standard American diet is very heavily over-weighted with omega-6s (See “Report Finds Americans Need Far More Omega-3s”).
Omega-3s come mainly from fish (richest source by far) and green plant foods or flaxseed (adequate source, if eaten in abundance).
Omega-6s predominate in grains, seeds, common vegetable oils (corn, safflower, sunflower, cottonseed, soy), the prepared and packaged food made with these cheap oils, and grain-fed meats, fish, and poultry. While still high in omega-6s, canola oil has less than most oils and offers more omega-3s and monounsaturates.
The few vegetable oils low in omega-6s include olive, macadamia, flax, and hi-oleic sunflower.
Analysis reveals nutritional downside to farmed fish
The unnatural, diet-driven fat profile of farmed fish gets almost no attention, despite the scientific consensus that the omega-3/omega-6 intake ratio is a critical health factor.
The authors of the new study expressed this woeful oversight well:
“Although a great deal of attention has been focused on the contamination of farmed fish populations with methyl mercury, polychlorinated biphenyls [PCBs], and other organic compounds, little has been published with regard to the effects of rapid changes in the fish industry on [polyunsaturated fatty acid] PUFA or saturated fatty acid (SFA) levels in emerging, intensively farmed species of fish.”
And their results confirm the importance of focusing on this issue, as people to move eat more and more—mostly farmed—fish.
We take no pleasure in reporting bad nutritional news about farmed Tilapia and Catfish, which are mostly raised onshore, often in a sustainable fashion, and should be healthful foods.
But the Wake Forest University research reveals what we could have predicted: fish raised largely on omega-6-rich grains (corn, mostly) and seed oils (corn, soy, etc.) develop unhealthful fat profiles that they pass on to consumers (Weaver KL et al. 2008; Komprda T et al. 2005).
(See “Farmed Salmon's Diet Yields Unhealthful Cardiovascular Effects” and search our newsletter archive.)
This excerpt from the paper’s introduction presents the essence of what they found:
“Our research reveals certain intensively farmed species of fish contain PUFA profiles that have been shown to be detrimental to human health” (Weaver KL et al. 2008).
Their analysis revealed key facts about the world’s top four farmed fish:
Farmed Tilapia and Farmed Catfish Prove Poor Choices
- Low levels of omega-3s (about one-fourth as much as in farmed or wild Salmon; omega-3 levels were a bit higher in Catfish than Tilapia)
- High levels of omega-6s (average 134 mg per 110 grams in Tilapia, 67 mg per 100 grams in Catfish)
- Very high omega-6/omega-3 ratios
- Unfavorable ratios of saturated fats and monounsaturated fats to polyunsaturated fats
Farmed Trout and Farmed Atlantic Salmon Rank Better, but Not Great
- Relatively high levels of omega-3s
- Relatively low (but still unhealthful) omega-6/omega-3 ratios
- Favorable ratios of saturated fats and monounsaturated fats to polyunsaturated fats
Researchers usually measure total omega-3 and omega-6 levels when assessing the health benefits of a fish.
But very little of the short chain omega-3 called alpha-linolenic acid gets converted to the long-chain omega-3s needed in cell membranes (EPA and DHA), so including it overstates the healthfulness of a fish.
Consequently, the researchers chose to focus on the levels and ratios of the two primary long-chain omega-6s and omega-3s that influence inflammation in the body: omega-6 arachidonic acid (AA) and omega-3 EPA.
Both farmed Tilapia and Catfish contained high ratios of omega-6 AA to omega-3 EPA.
The average AA/EPA ratio in farm-raised Tilapia was 11:1, with two fish samples from Central America containing about 20 times more omega-6 AA than omega-3 EPA.
As the Wake Forest team wrote, “Taken together, these data reveal that marked changes in the fishing industry during the past decade have produced widely eaten fish that have fatty acid characteristics that are generally accepted to be inflammatory by the health care community.”
Inflammation is widely accepted as a key driving force behind “lifestyle” conditions such as cardiovascular disease, diabetes, cancer, and dementia.
And, as the authors explain in well-documented detail, one of the most important influences on inflammation is the amount of omega-6 arachidonic acid in our cell membranes.
In fact, many of the benefits associated with long chain omega-3s (EPA and DHA)—which are abundant only in fatty fish—stem from the fact that they exert anti-inflammatory effects.
High intake of marine omega-3s prevents omega-6 AA from dominating our cell membranes, where they tend to spark and sustain unhealthful “silent” inflammation.
These excerpts from the new report pinpoint the problem with farmed fish:
- “...the US Department of Agriculture… reports that farm-raised Atlantic Salmon contains more than 1 g dietary [omega-6] arachidonic acid per 100 g fish. If this is correct, farmed Salmon is by far the richest source of [omega-6] arachidonic acid in most Western diets and raises important questions regarding its consumption, especially by vulnerable populations.”
- “The concentrations of [omega-6s]… in farmed tilapia and catfish are very high. In fact, these fish contain some of the highest levels of [omega-6] arachidonic acid found in human beings’ food chain.”
There was considerable variation in the omega-6 content of Tilapia raised in different places, but the tests of Tilapia samples from Central America—a major US source—showed more than 300 mg of omega-6 arachidonic acid per 100 gram (3.5 oz) serving.
In contrast, the same size portion of hamburger (80% lean) contains about one-tenth that level of arachidonic acid (only 34 mg).
And at 191 mg, even a same-size piece of pork bacon contains much less omega-6 than some Tilapia does!
As the authors wrote, “For individuals who are eating fish as a method to control inflammatory diseases such as heart disease, it is clear from these numbers that Tilapia is not a good choice. All other nutritional content aside, the inflammatory potential of hamburger and pork bacon is lower than the average serving of farmed Tilapia” (Weaver KL et al. 2008).
Sadly, the “vulnerable populations” they cite include most Americans, whose diets are already awash in omega-6s and sorely lacking in omega-3s.
Those most vulnerable to ill effects from excess dietary omega-6s include people with risk factors for cardiovascular disease, diabetes, cancer, dementia, allergies, or auto-immune conditions such as rheumatoid arthritis… whether genetic, lifestyle, or weight-related.
The Wake Forest team noted that some prior findings seem to downplay the detrimental effect of high omega-6 intake on cardiovascular health, assuming that as long as omega-3 intake is also high, those effects are mitigated (Harris WS et al. 2007).
This claim contradicts considerable amounts of epidemiological evidence.
The sophisticated analysis of the Wake Forest team delves deeply into the devilish details of fatty acid science, and calls those prior, misleading claims into serious question.
Reuters Health’s report makes major Salmon mistake
As we noted, we heard about the new study from Rebecca Katz, who forwarded coverage of the research by Reuters Health.
Unfortunately, their summary contained a gross and misleading error (underlined):
“When they specifically compared the four most commonly farmed fish—Alaskan Salmon, Trout, Tilapia and Catfish—the researchers found that the latter two had much more omega-6 than omega-3 fat…”
That line should have read Atlantic salmon, not Alaskan. In fact, Salmon farming is banned in Alaska!
While Alaska does have wild Salmon hatchery programs, the smolts are released into the wild at a young age and grow to maturity on a completely natural diet.
The vast majority of farmed Salmon is Atlantic Salmon: a distinct species that cannot successfully mate with any of the five species of Pacific Salmon: King (Chinook), Sockeye (Red), Silver (Coho), Pink, and Keta (Chum).
Two Pacific Salmon species—King (Chinook) and Silver (Coho)—are industrially farmed in British Columbia and other parts of the world.
Presumably, like farmed Atlantic Salmon, the fat profiles of farmed Pacific Salmon also suffer from the effects of cheap, grain-based diets.
- Harris WS, Poston WC, Haddock CK. Tissue n-3 and n-6 fatty acids and risk for coronary heart disease events. Atherosclerosis. 2007;193: 1-10.
- Komprda T, Zelenka J, Fajmonová E, Fialová M, Kladroba D. Arachidonic acid and long-chain n-3 polyunsaturated fatty acid contents in meat of selected poultry and fish species in relation to dietary fat sources. J Agric Food Chem. 2005 Aug 24;53(17):6804-12.
- National Public Radio (NPR). Is The Farm-Raised Fish Tilapia Good for You? July 11, 2008. Accessed online July 13, 2008 at http://odeo.com/episodes/23072824-NPR-On-Health-for-July-11-2008
- Norton A. Fatty fish not equal in "good" fats: study. July 11, 2008. Reuters Health. Accessed online July 13, 2008 at http://www.nlm.nih.gov/medlineplus/news/fullstory_66838.html.
- Seierstad SL, Seljeflot I, Johansen O, Hansen R, Haugen M, Rosenlund G, Froyland L, Arnesen H. Dietary intake of differently fed salmon; the influence on markers of human atherosclerosis. Eur J Clin Invest. 2005 Jan;35(1):52-9.
- Weaver KL, Ivester P, Chilton JA, Wilson MD, Pandey P, Chilton FH. The content of favorable and unfavorable polyunsaturated fatty acids found in commonly eaten fish. J Am Diet Assoc. 2008 Jul;108(7):1178-85.