Bottom-Line: Diets high omega-6 to omega-3 fat may lead to obesity, according to results of an animal study. Cardiovasc Psychiatry Neurol. 2009;2009:867041.

Background: Adipose tissue is more than a dormant energy storage depot. Fat cells, known as adipocytes, release chemical mediators, which promote inflammation. This may be the key link between obesity and increased risk of inflammatory diseases.

Emerging research in both animal and human studies indicate that eating excessive amounts of dietary omega-6 fat combined with insufficient amounts of omega-3 fats might be a risk factor for obesity [2].

Notably, decades ago, researchers fed men a diet with the same amount of calories, but differed in fat composition. After a five-year period, the men eating a high omega-6 fat diet gained weight by 3%, compared to the control group, which lost 2% of their body weight. The rate of linoleic acid (omega-6 fat) accumulation was positively associated with weight gain [2].

Omega-6 fats are the chief polyunsaturated fat eaten in westernized countries. In the last century, consumption of so-called "heart healthy" omega-6 fats has skyrocketed, while dietary omega-3 intake has declined.

Study: The purpose of this study was to evaluate the possible pathophysiological consequences of eating a disproportionate amount of omega-6 to omega-3 dietary fatty acids, on body weight and organ function.

Three generations of mice were fed isocaloric diets, in which alpha-linolenic acid (the omega-3 precursor of EPA), was replaced with linoleic acid, the chief omega-6 polyunsaturated fat found in vegetable oils.

The experimental group's diet was lower in omega-3 fat with a higher omega-6 level, compared to the control group (0.16% calories versus 1.0% calories), and (12.3% calories versus 9.7% calories), respectively.

Results: Mice eating the experimental diet, had a significant increase in body weight with detrimental consequences on the liver, heart and kidney, compared to mice fed the standard diet.

Moreover, adipogenesis was accompanied by a 6-fold elevation of a key enzyme (stearyl-CoA desaturase), which is related to plasma triglycerides and fatty liver. An increase in the dietary omega-6/omega-3 fat ratio, up-regulated the key gene required to make this enzyme.

Conclusion: The researchers concluded that long-lasting omega-3 fat deficiency combined with eating excess dietary omega-6 fats, affects the liver function in a manner, which may lead to obesity.

Study Quote: "Extrapolation of the present data to human populations showed a stark parallel to the increased dietary intake of omega-6 fats in most developed countries in the last 100 years. Due to the competitive relationship between omega-3 and omega-6 fats the inevitable increase of the omega-6 HUFA pool may irreversibly lead to both obesity and the inflammation resulting in increased mortality."

Links to References:

[1] Hanbauer I, Rivero-Covelo I, Maloku E, Baca A, Hu Q, Hibbeln JR, Davis JM.The Decrease of n-3 Fatty Acid Energy Percentage in an Equicaloric Diet Fed to B6C3Fe Mice for Three Generations Elicits Obesity. Cardiovasc Psychiatry Neurol. 2009;2009:867041. Free Full Text

[2] Gérard Ailhaud, Philippe Guesnet and Stephen C. Cunnane (). An emerging risk factor for obesity: does disequilibrium of polyunsaturated fatty acid metabolism contribute to excessive adipose tissue development?. British Journal of Nutrition, (2008), 100: 461-470. Free Full Text.