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Food, Health, and Eco-news
Excess Omega-6 Fat Intakes Promote Weight Gain
Joyce Nettleton, D.Sc., presents the second in a series of reports on news from the recent fat-science summit meeting 02/16/2011 by Joyce A. Nettleton, D.Sc.
Last month, we attended two omega-3 science conferences in Europe (See “Omega-3 Gurus Savor Vital Choice Salmon.”)
Both were attended by the world's leading fatty acid research scientists, and featured a wealth of new findings and insights.
The second of the two meetings was 2010 gathering of the International Society for Study of Fats & Lipids (ISSFAL), held in Maastricht, the Netherlands.
We asked expert attendee Joyce Nettleton, D.Sc., to summarize the ISSFAL presentations that addressed various topics, including brain, heart, and metabolic health.
Dr. Nettleton is a widely published expert on omega-3 science and seafood health-nutrition topics. She issues regular fatty acid science updates in her great Fats of Life (consumer-oriented) and PUFA (scientist-oriented) e-newsletters.
Her first report concerned omega-3s' apparent or potential impacts on metabolism, with implications for the risk of metabolic syndrome (MetS) and the diabetes it often forecasts.
Tonight, we present the second of her reports, with this one focused on the role of dietary omega-6 fats in weight gain and control.
Omega-6 fats constitute far more of American's fat intake than they did just 200 years ago, and much more than humans adapted to over millennia of evolution… a shift with serious health implications.
The omega-6 fat of greatest concern is linoleic acid (LA) from vegetable oils, which competes with omega-3 fats for absorption into our cells. 
Omega-6 LA predominates in most vegetable oils, nuts, seeds, corn, grains, and meat from the vast majority of livestock, which are fed corn, soy, and grains.
While omega-3 fats reduce inflammation, omega-6 fats tend to promote it. Unfortunately, the American diet is grossly imbalanced in favor of omega-6 fats, with documented damage to their health.

Some vegetable oils—olive, macadamia, and hi-oleic sunflower—are especially low in omega-6 fatty acids… see “Canola Oil Controversy” in this issue.
Note: Wherever Dr. Nettleton refers to omega-6 fats below, she is referring to the short-chain, plant-source form called LA.
Do Omega-6 Fatty Acids Promote Fat Accumulation?
By Joyce Nettleton, D.Sc.
Diets high in omega-6 fatty acids are associated with greater body weight and fat compared with diets having less omega-6 fat and more omega-3 fat.
Several studies presented at the recent ISSFAL conferfence seem to support prior research results.
Mouse study finds omega-6 fats promote weight gain
At the ISSFAL conference, researchers reported that mice fed 50 percent less omega-6 fat than the control group for the first 6 weeks of life and then switched to a western-style diet (high in omega-6 fat) for eight weeks had 27 percent less fat compared with the controls.
The rodents also had fewer fat cells, lower blood triglyceride (fat) levels, improved glucose (blood sugar) tolerance, and greater insulin sensitivity… all of which are associated with reduced risk for diabetes and heart disease (Oosting A et al., 2010).
American babies' bellies grew along with increasing omega-6 intake
The type of dietary fat a person eats affects the development of metabolic syndrome (MetS).
Population studies suggest that diets high in saturated fats increase the chance of developing MetS, while high polyunsaturated fat lower the risk.
Whether diets high in omega-6 fat promote weight gain and fat accumulation and contribute to MetS is hotly debated.
Adipositythe medical term for excess belly fat—in six to 11-month old infants in the U.S. increased nearly two-fold from 1976 to 1994.
This sharp rise occurred during the same time span when the omega-6 fat content of infant foods, including breast milk and infant formula, also increased (Alvheim A, 2010).
In contrast, infants' intake of omega-3s declined during this period.
Associations like these do not establish cause-effect relationships, but they raise questions.
Infant mice show similar reaction to diets high in omega-6 fats
French researchers have reported that a western-like diet is sufficient to induce greater fat mass over generations (Massiera F, et al. 2010)... and a study in mice presented at ISSFAL also addressed this issue.
Mice consumed diets containing either one or eight percent omega-6 fat from weaning (Alvheim A, 2010).
Those on the eight percent omega-6 fat diet exhibited significantly greater appetite, feed efficiency and fat tissue compared with those on the one percent omega-6 fat diet.
Adding one percent of energy from long-chain omega-3 fish fats (EPA and DHA) to the eight percent omega-6 fat diet was accompanied by reduced fat accumulation and lower feed efficiency, which means that fewer of the animals' calories were absorbed.
The French team noted that even diets that were extremely high in fat (60 percent of calories)but in which omega-6 fat contributed only one percent of total calories—did not produce obesity.
Omega-3s may lower risk factors for cardiovascular disease and diabetes
In one invited ISSFAL presentation, the speaker noted that lifestyle modifications, such as the inclusion of long-chain omega-3 fats from fish (EPA and DHA) can help deter development of obesity, liver-fat accumulation, abnormal blood fat profiles and impaired glucose tolerance (Kopecky J, 2010).
But once diabetes has developed, these fatty acids are much less effective and drugs are necessary to reverse obesity, abnormal lipids and insulin resistance.
The potential for preventing MetS and ultimately diabetes by increasing long-chain omega-3 fatty acid intake—in conjunction with reducing omega-6 fat consumption—deserves much more investigation and attention.
“Mono” fats appear to bear little blame for weight gain
We've had relatively little evidence on how diets rich in monounsaturated fats—chiefly, the oleic acid in olive, macadamia nut, canola and “high-oleic” sunflower oil—affect the risk of metabolic syndrome (MetS), though there is as yet no evidence that mono-unsaturated fats raise it.
At the conference, investigators from Spain reported that MetS patients with the highest proportion of monounsaturated oleic acid in their blood had less abdominal obesity and were more likely to have higher (more desirable) HDL levels.
These observations suggest that in addition to protecting heart health, diets rich in olive oil may help to deter weight gain (Sala-Vila A et al., 2010).
  • Alvheim A, Osei-Hyiaman D, Robert P, et al. Dietary linoleic acid promotes hyperactive hepatic 2-arachdonoyl-glycerol and contributes to diet-induced obesity. Abstract. ISSFAL 2010, Maastricht, Netherlands. P 106.
  • Kopecky J. Multiple mechanisms of action of n-3 fatty acids on metabolismpossible impact for the treatment of metabolic syndrome. Abstract. ISSFAL 2010, Maastricht, Netherlands. P 108.
  • Oosting A, Kegler D, Boehm G, et al. Reduced n-6 polyunsaturated fatty acids during postnatal development prevents excessive fat deposition and improves metabolic profile in adult mice. Poster. ISSFAL 2010, Maastricht, Netherlands. P 83.
  • Sala-Vila A, Cofan M, Cenarro A et al. Inverse association between the proportion of oleic acid in serum phospholipids and metabolic syndrome traits in a dyslipidemic Spanish population. Poster. ISSFAL 2010, Maastricht, Netherlands. P 99.


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