Eskimos have been shown to possess lower prevalences of insulin resistance, metabolic syndrome and type 2 diabetes compared to non-Eskimo Native Americans. This has been suggested to be due to the higher intake of omega-3 fatty acids in the diet of the Eskimos. Omega-3 fatty acids have anti-inflammatory effects and this may in turn decrease oxidative stress. As oxidative stress has been hypothesised to increase insulin resistance, fish oils may improve insulin sensitivity and have positive effects of the insulin system. If this is true, then it would be expected that omega-3 fatty acids would have weight loss effects through their insulin sensitising effects. Fish are rich in long chain omega-3 fatty acids and evidence suggests that fish oils can sensitise the insulin system and this may explain some or all of the fat loss effects seen with increasing fish consumption. The high consumption of fish in certain Mediterranean areas has also been suggested to be responsible for the improved health of populations located here.
Consuming more seafood may therefore confer weight loss benefits. Researchers1 have investigated the effects of consuming seafood of weight loss in healthy overweight and obese individuals. In a randomised, single blinded trial, researchers fed either lean fish comprising of 150 grams of cod 3 times per week (supplying 0.3 grams omega-3 fatty acids per day), fatty fish comprising of 150 grams of salmon 3 times per week (supplying 3 grams omega-3 fatty acids per day), fish oil capsules (supplying 1.5 grams omega-3 fatty acids per day) or a control diet comprising of sunflower oil capsules (supplying no omega-3 fatty acids). The rest of the diets of the subjects was standardised and restricted energy by around 30 %. The results showed that inclusion of seafood into the diet resulted in approximately 1 kg greater weight loss compared to the placebo after 4 weeks of consuming a standard energy restricted diet. Sea food may therefore provide some benefits to weight loss in the short term in overweight and obese subjects.
The researchers also measured the omega-3 fatty acid content of the erythrocyte phospholipids of the subjects. The subjects consuming seafood had higher omega-3 fatty acid in their phospholipids compared to the control group at the end of the study, and this may have been related to the inclusion of seafood to the diet. Omega-3 fatty acids have a pronounced anti-inflammatory effect because they are able to block formation of the pro-inflammatory eicosanoids derived from the omega-6 fatty acid arachidonic acid. Inflammation is a cause of oxidative stress and oxidative stress is known to decrease insulin sensitivity. This may explain the known insulin sensitising effects of omega-3 fatty acids, and may partly explain the weight loss benefits observed in this study following supplementation with seafood. As expected the salmon and fish capsule groups showed greater elevations in their phospholipid membranes compared to the cod group, the latter being a poorer source of omega-3 fatty acids.
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