Does fast food contribute to depression?
Can a healthy diet combat mental illness?
In an unusual experiment, James Cook University researchers in Australia have found that among Torres Strait Islander people the amount of fish and processed food eaten is related to depression.
A JCU research team led by Professors Zoltan Sarnyai and Robyn McDermott looked at the link between depression and diet on a Torres Strait island, where fast food is available, and on a more isolated island, which has no fast food outlets.
Dr. Maximus Berger, the lead author of the study, said the team interviewed about 100 people on both islands.
“We asked them about their diet, screened them for their levels of depression and took blood samples.
As you’d expect, people on the more isolated island with no fast food outlets reported significantly higher seafood consumption and lower take-away food consumption compared with people on the other island,” he said.
The researchers identified nineteen people as having moderate to severe depressive symptoms: sixteen were from the island where fast food is readily available, but only three from the other island.
“People with major depressive symptoms were both younger and had higher take-away food consumption,” said Dr. Berger.
The researchers analysed the blood samples in collaboration with researchers at the University of Adelaide and found differences between the levels of two fatty acids in people who lived on the respective islands.
“The level of the fatty acid associated with depression and found in many take-away foods was higher in people living on the island with ready access to fast food, the level of the fatty acid associated with protection against depression and found in seafood was higher on the other island,” said Dr. Berger.
He said it was important to remember that contemporary Western diets have an abundance of the depression-linked fatty acid (n-6 PUFA) and a relative lack of the depression-fighting fatty acid (n-3 LCPUFA).
Omega−3 fatty acids are important for normal metabolism. Mammals are unable to synthesize omega−3 fatty acids, but can obtain the shorter-chain omega−3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega−3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds).The ability to make the longer-chain omega−3 fatty acids from ALA may be impaired in aging. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity
Omega-6 fatty acids are precursors to endocannabinoids, lipoxins, and specific eicosanoids.
Medical research on humans found a correlation (though correlation does not imply causation) between the high intake of omega-6 fatty acids from vegetable oils and disease in humans. However, biochemistry research has concluded that air pollution, heavy metals, smoking, passive smoking, lipopolysaccharides, lipid peroxidation products (found mainly in vegetable oils, roasted nuts and roasted oily seeds) and other exogenous toxins initiate the inflammatory response in the cells which leads to the expression of the COX-2 enzyme and subsequently to the temporary production of inflammatory promoting prostaglandins from arachidonic acid for the purpose of alerting the immune system of the cell damage and eventually to the production of anti-inflammatory molecules (e.g. lipoxins & prostacyclin) during the resolution phase of inflammation, after the cell damage has been repaired.
“In countries with a traditional diet, the ratio of n-6 to n-3 is 1:1, in industrialised countries it’s 20:1,” he said.
Professor Sarnyai said depression affects about one in seven people at some point in their lives and Aboriginal and Torres Strait Islander people are disproportionately affected by psychological distress and mental ill-health compared with the general population.
“Depression is complex, it’s also linked to social and environmental factors so there will be no silver bullet cure, but our data suggests that a diet that is rich in n-3 LCPUFA as provided by seafood and low in n-6 PUFA as found in many take-away foods may be beneficial,” he said.
Professor Sarnyai said with the currently available data it was premature to conclude that diet can have a lasting impact on depression risk but called for more effort to be put into providing access to healthy food in rural and remote communities.
“It should be a priority and may be beneficial not only to physical health but also to mental health and wellbeing,” he said.
More information: Maximus Berger et al, Cross-sectional association of seafood consumption, polyunsaturated fatty acids and depressive symptoms in two Torres Strait communities, Nutritional Neuroscience (2018). DOI: 10.1080/1028415X.2018.1504429
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