Paris, 16 July 2010
Omegas 6 and 3 are essential polyunsaturated fatty acids: they are indispensable to the human body, which cannot produce them itself and must therefore source them from food. Omega 6 are normally found in maize, which is itself consumed in large quantities by the farmed animals eaten by humans (half of our lipid intake comes from meat and dairy products). As for omega 3, they are mainly present in grass, linseed, rapeseed and fatty fish such as salmon, sardine or mackerel (which contain very high levels of alpha-linoleic acid). In the past forty years, there has been a steady rise in obesity over the generations in Western societies. During the same period, the diet in industrialized countries has seen a quantitative increase in the calories ingested (lipids account for 35 to 40% of food intake), high levels of linoleic acid (omega 6) and low levels of alpha-linoleic acid (omega 3). Indeed, the amount of omega 6 consumed during the past forty years has rocketed (+250%) while that of omega 3 has fallen by 40%, thus destabilizing the omega 6/omega 3 ratio when compared with the recommended intakes. While the French Food Safety Agency (AFSSA) recommends an omega 6/omega 3 ratio of 5/1, actual consumption is 15 omega 6 for 1 omega 3. In the USA, this ratio can even reach 40 omega 6 for 1 omega 3.
To perform their experiments, the researchers exposed four generations of mice to a Western-style diet, characterized by these same omega 6/omega 3 ratios. As a result, they saw a gradual increase in fat mass over several generations. They also observed the onset of metabolic disorders such as insulin resistance, which is the first step in the development of type 2 diabetes and a stimulation of the expression of the inflammatory genes involved in obesity.
Thus, in a genetically-stable animal population, exposure to a diet similar to that of developed or developing countries was sufficient to cause the emergence of transgenerational obesity, in line with the data collected in humans. The beneficial role of essential polyunsaturated fatty acids such as omega 6 (linoleic acid) is well-known in the treatment of hypercholesterolemia, and that of omega 3 in cerebral function. But when their intake is unbalanced, these fatty acids can enhance the factors inducing obesity and have serious long-term effects on human health. The agrifood industry needs to take greater account of the implications of these findings.
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Fourth generation of mice rendered obese by a "Western-like" diet (left) compared with a mouse kept on a standard diet (right).
(1) Institut de Biologie du Développement et Cancer (IBDC, CNRS/Université de Nice), Institut de Pharmacologie Moléculaire et Cellulaire (IPMC, CNRS/Université de Nice), Unité de Biologie fonctionnelle et adaptative EAC 7059 (CNRS/Université Paris Diderot).
(2) Unité de Nutrition et Régulation Lipidique des Fonctions Cérébrales (NuRéLiCe) UR909, 78352 Jouy en Josas cedex, France.
Massiera et al. A Western-like fat diet is sufficient to induce a gradual enhancement in fat mass over generations. J. Lipid Res. 2010; Vol 51 : pp 2352-2361 © the American Society for Biochemistry and Molecular Biology. August 2010 issue.
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