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Omega-3-rich fish oils have long been recommended for heart health, decreasing inflammation, and brain and eye health. A 2015 study out of Kyoto University found that a diet rich in fish oil helped convert fat-storage cells to fat-burning cells, which could help prevent middle-age weight gain. The body has three types of fat cells: white fat cells, which store fat, brown fat cells, which burn calories to heat the body and are found abundantly in infants, and beige fat cells, which can function like brown fat cells.
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They fed a group of mice two diets – one rich in fish oil and one high in other types of fat – and found that the mice that consumed the fish oil diet gained less weight and less fat than the mice fed the other mix. They also found that beige fat cells formed from white fat cells when the sympathetic nervous system was activated, meaning that certain fat-storage cells have the ability to convert to metabolizing cells, which can assist in weight loss.