High n-6/n-3 ratio diet during development may affect brain's reward system
Scientists at Japan’s Hiroshima University report that offspring of pregnant mice fed diets with a very high omega-6 to omega-3 fatty acid (n-6/n-3) ratio exhibit more overeating behaviours. If this pattern holds for humans too, although human diets are less extreme than that used here, then addressing the diets of pregnant women could help prevent obesity in the offspring. The study is published in Communications Biology.
Fish and flaxseed are high in omega-3 fatty acids while omega-6 fatty acids are found in corn oil, nut and seed oil. Surveys suggest that in the 20th century, intake of omega-6 fatty acids has increased and intake of omega-3 fatty acids has decreased. This change has been fuelled by changes in soyabean and vegetable oil consumption, and intensive livestock rearing (Balsbalg and colleagues 2011, Sanders et al. 2000). The ratio of the two fatty acids in our diets has therefore been changing.
This ratio is thought to be important for obesity risk. Studies in young animals suggests maternal intake of a high n-6/n-3 diet can influence later obesity but so far studies in man do not always support this idea (see Further Reading). This study builds on a previous one using the same animal model and diet which suggested that a maternal diet with a high n-6/n-3 ratio could alter brain functioning in offspring. It investigates if there is any influence of the diet on the brains food reward systems, which could explain the link to obesity.
The researchers led by Nobuyuki Sakayori divided 11-week old female mice into two groups and fed them a diet either with a n-6/n-3 ratio of 7.4 ± 0.5 (controls) or 121.4 ± 1.9, (high n-6/n-3 group). The mice were mated and then fed through pregnancy and lactation with the same diet. The two groups had similar bodyweight. However, adult offspring from the high n-6/n-3 group had higher amounts of omega-6 and decreased amounts of omega-3 in the brain compared with control mice.
In tests using palatable sucrose solutions in concentrations from 1% to 30%, the researchers found that mice from dams fed the high n-6/n-3 diet would choose high sucrose solutions more often than controls when given a choice. The mice were more motivated to work for a dose of 10% sucrose solution than controls. The consumption wasn’t specific to sucrose solutions. The offspring of high n-6/n-3 mice would consume more of a high sucrose or a high fat diet after food deprivation compared with control mice.
Dopamine is known to be released when highly palatable foods are eaten as part of the ‘reward’ system of the brain. The researchers looked at the release of dopamine in the brain for the two groups of mice. They found that the offspring of mice fed the high n-3/n-6 diet had higher baseline levels of this brain chemical. The same mice responded to consuming sucrose by releasing more dopamine compared with control mice.
The results suggest that the n-6/n-3 ratio in early diet predisposes mice to obesity by affecting their behavioural responses to highly palatable foods..
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Reference
Sakayori, N., Katakura, M., Hamazaki, K., Higuchi, O., Fujii, K., Fukabori, R., Iguchi, Y., Setogawa, S., Takao, K., Miyazawa, T., Arita, M. & Kobayashi, K.. Maternal dietary imbalance between omega-6 and omega-3 fatty acids triggers the offspring’s overeating in mice. Communication Biology 3, 473 (2020). https://doi.org/10.1038/s42003-020-01209-4