The specific diet triggers were soft drinks, fatty red meat and refined grains such as pasta, white bread and chips.
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Dr. Michael Lucas, a Harvard researcher who co-authored the study, said the causes of mood disorders are hard to pinpoint. He said it's not clear how inflammation affects mental health, but there does appear to be a link.
Food choices that help keep inflammation down include olive oil, coffee, wine, carrots, sweet potatoes and leafy greens, Lucas said.