Farmed salmon diet fattens mice.
|
Ibrahim, MM, E Fjære, EJ Lock, D Naville, H Amlund, E Meugnier, B Le Magueresse Battistoni, L Frøyland, L Madsen, N Jessen, S Lund, H Vidal and J Ruzzin. 2011. Chronic consumption of farmed salmon containing persistent organic pollutants causes insulin resistance and obesity in mice. PLOS One http://dx.doi.org/10.1371/journal.pone.0025170. |
 |
| E. Peter Steenstra/U.S. Fish and Wildlife Service |
A study with mice provides more evidence that a diet high in farmed salmon contaminated by persistent organic pollutants - POPs - contributes to weight gain and increases the risk of diabetes.
The results are consistent with a growing body of research on people, linking POPs exposure to type 2 diabetes. Mice fed contaminated salmon gained twice as much weight and developed more severe insulin resistance measures than mice that ate no salmon but the same amount of fat.
When the researchers fed the mice salmon whose POPs levels had been reduced by around 50 percent, the health effects were also reduced.
The researchers could not say whether these effects are due entirely to POPs or other factors inherent in the fatty fish diet. Further work should test whether a complete avoidance of POPs further reduces weight gain and insulin resistance.
Context
Obesity is a growing problem around the world. The excessive weight gain is almost epidemic – especially in the United States, the European Union and other Western cultures where high-fat diets and low activity prevail.
At the same time, diabetes and other metabolic-related diseases also are increasing. These health conditions generally share an underlying cause: insulin resistance, which occurs when insulin becomes ineffective. Normally, the pancreas releases the hormone insulin to help cells take in and process glucose sugars. Cells use glucose as energy to fuel metabolism. Insulin resistence leads to too much insulin and glucose in the blood – and that affects metabolism.
Obesity, lack of exercise, genetics and high blood pressure are risk factors for insulin resistance. Collectively, the risks are called metabolic syndrome, and if left untreated, can lead to type 2 diabetes, stroke and other serious health issues.
In the United States, 25 percent of adults have metabolic disorders linked to insulin resistance. Diabetes alone affects 25.8 million people, about 8 percent of the population, according to the National Diabetes Information Clearinghouse.
Farmed salmon is one of the most commonly eaten fish worldwide. Fish are important sources of nutrients such as omega-3 fatty acids that benefit brain development and lower the risk of cardiovascular disease. But, eating fish may not deminish – and may in fact add to – the risk of diabetes, according to recent studies.
Like all fish, farmed salmon contain environmental contaminants. Among these are persistent organic pollutants (POPs). POPs are a large and varied group of chemical compounds that share certain traits, including persistence, toxicity to health and an ability to accumulate in tissues and fat. POPs were made and used in a variety of industrial and consumer applications. They are also byproducts of industrial processes.
A large survey comparing farmed with wild salmon has shown that POPs levels are significantly higher in farmed salmon than in wild.
The United States and other countries have banned the use and production of many POPs, yet, they still occur in wildlife, people and the environment at levels that can cause health concerns. POPs are linked to a long list of health effects, including cancer and diabetes.
What did they do?
In a new experiment using mice, scientists tested the effects of eating farmed salmon on weight gain and metabolism changes including insulin resistance, an indicator of diabetes. The researchers also tested whether POPs played a role in these factors.
The scientists fed groups of 8-week-old male mice different diets for eight weeks. These included a control diet, a very high-fat diet (72 percent fat) without farmed Atlantic salmon, a very high-fat diet with commercially-farmed Atlantic salmon and a lower fat/high carbohydrate Western-style diet (29 percent fat) with or without salmon.
Another group of mice was fed salmon whose POPs levels had been reduced by approximately 50 percent.
The researchers measured weight gain, body fat to track obesity and insulin resistance and glucose tolerance, both of which indicate increased risk of developing diabetes. They also measured levels of POPs in tissues and fat, including organochlorine pesticides, dioxins, furans and different types of polychlorinated biphenyls.
What did they find?
What does it mean?
The study with mice provides more evidence that eating a prolonged diet with contaminated fatty fish may increase obesity and raise the risk of insulin resistence that may lead to diabetes. While the exact reasons for the changes aren't clear, pollutants in the fish contributed some to the increased risk of metabolic disease seen in the study, the researchers report.
The results show that eating the POPs-contaminated farmed salmon led to greater weight gain and higher predisposition to type 2 diabetes compared to a salmon-free diet with the same amount of total fat.
The findings raise a number of questions, including whether this pattern is true for all fish – farmed or not – or seafood in general and if it carries over to other fatty, foods, such as meat and dairy, which may also contain POPs. The researchers could not say whether these effects are due entirely to POPs or other factors inherent in the fish diet. Further research should test whether a complete avoidance of POPs further reduces weight gain and insulin resistance.
Prior research has tried to understand the influence of fish intake on type 2 diabetes and other metabolic diseases. Yet, the interplay between the two remains ambiguous. Overall, recent long-term human studies from the United States and Europe suggest a connection.
This experimental study is one of the first to test the idea in animals. The study supports those past human studies because it finds similar results.
Other lab and animal studies by the same research group have found POPs can interfere with the beneficial effects of salmon oil and impair insulin actions. This study suggests the same but provides a new twist. It is unique because whole fish fillets – not just fish oil alone – were used.
POPs levels in the fish's fatty tissues were similar to what has been measured in the people. This agrees with past research showing that environmentally relevant levels of one type of POPs – polycyclic byphenyls (PCBs) – can affect insulin resistance.
Since salmon are a complex mix of many different nutrients and contaminants, it will require more intensive study to uncover the mechanism behind these patterns. For right now, the researchers suggest that limiting "daily and long-term exposure to POPs may therefore represent a novel and attractive approach to slow down the uncontrolled rise of metabolic diseases."
ResourcesDjousse L, JM Gaziano, JE Buring and IM Lee. 2011. Dietary omega-3 fatty acids Grundy SM, JI Cleeman,SR Daniels, KA Donato, RH Eckel, BA Franklin, DJ Gordon, RM Krauss, PJ Savage, SC Smith, Jr, JA Spertus and F Costa. 2005. Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute scientific statement. Circulation:112:2735-2752. Hites, RA, JA Foran, DO Carpenter, MC Hamilton, B Knuth, and SJ Schwager 2004. Global Assessment of Organic Contaminants in Farmed Salmon. Science 2004: 226-229. Kaushik. M, D Mozaffarian, D Spiegelman, JE Manson, WC Willett and FB Hu. 2009. Long-chain omega-3 fatty acids, fish intake, and the risk of type 2 diabetes mellitus. American Journal of Clinical Nutrition 90:613-620. Lee D-H, Steffes MW, Sjo¨ din A, Jones RS, Needham LL, et al. (2011) Low Dose Organochlorine Pesticides and Polychlorinated Biphenyls Predict Obesity, Dyslipidemia, and Insulin Resistance among People Free of Diabetes. PLoS ONE 6(1): e15977. Meyer, KA, LH Kushi, DR Jacobs and AR Folsom. 2001. Dietary fat and incidence Ruzzin, J, R Petersen, E Meugnier, L Madsen, EJ Lock, et al. 2010. Persistent van Woudenbergh, GJ, AJ van Ballegooijen, A Kuijsten, EJG Sijbrands, FJA van |
The above work by Environmental Health News is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
Based on a work at www.environmentalhealthnews.org.
POPs and diabetes
